The Chemistry of Dyestuff. Dyestuffs. Appendix, Drawings Of Plant.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)




FIG. I Ordinary Tar Still.


FIG. II. Plant for Distillation of Coal Tar Oils, Rectification of Oils, etc.


A Still, steam-heated.
B Savalle column, still-head.
C Air-cooler or condensator.
D Condenser proper (water tubes).

Interior Section of Column B-b. Dephlegmator.
O Overflow pipes.
W Wells.
P Perforated plates.
F Tiny fountains caused by vapour ascending, giving good fraction ation.




FIG. III. Plant for Manufacture of Diphenylamine Products.
A Autoclave.
B Vat for washing, dissolving out impurities.
C Table filter.



FIG. IV. Sulphonation Plant used in Manufacture of Benzene Sulphonates, etc.
A Autoclave with Stirrer and Gauge.
B Condenser for Excess Hydrocarbon.
C Receiver.
D Agitating vessel for neutralisation, "timing-out," etc.




FIG. V. Plant for Manufacture of Dimethylaniline.

A Autoclave in oil-bnth.
B Still (stirrer with hollow spindle for steam).
C Condenser.
R Receiver.

D Feed-pump.
E Separating vessel.
F Carboy.


FIG. VI. Plant for Manufacture of Naphthol products from Sulphonic Acids, e.g. Amidonaphthol sulphonic acid Y (2, 8, 6) from β-naphthylamine disulphonic acid G by heating under pressure with alkali.
A Pressure vessel for alkali melt.
B Vessel for neutralisation of alkali melt (with stirrer).
C Filter press.





FIG. VII. Plant for Kapid Distillation and Purification. Used in purification of Eesorcine.

A Retort-still.
B Condenser.
C Receiver.
D Moulds.


FIG. VIII. Plant for Alkylating, etc. under Pressure.
G Pressure gauge.
V Safety valve.
S Stirrer.





FIG. IX. Plant for Solvent Extraction and Separation, e.g. used of extraction of Kesorcine with Amyl Alcohol and Ether.
A Extraction vessel with spiral agitator.
B Separating vessels.
C Still for recovery of solvent


FIG. X. Evaporating and Grinding Plant used in Manufacture of Intermediate Products and Dyestuffs, Dyewood Extracts, etc.
A Supply pipes.
B Reservoir heaters.
C Evaporating pans (steam-jacketed).
D Grinding mills.



FIG. XI. Plant for Manufacture of an Azo Dyestuff.
A Vat for diazotising the amine component (with paddle agitator).
B Vessel for dissolving second component (phenol or amine).
C Coupling vat (with agitator).
D Monteju (receiving reservoir).
E Filter press.
N Vessel for sodium nitrite.

FIG. XII. Special Plant for Manufacture of an Azo Dyestuff.
A Autoclave for sulphonation, or dissolving, or diazotisation under pressure.
B Receiver from A for neutralisation, dilution, etc. if required.
C Coupling vat (tandem paddle stirrers).
D Vessel for dissolving or diazotising second component.
E Pump feeding press.
F Filter press.

The Chemistry of Dyestuff. Dyestuffs. XXVI. Natural Dyestuffs.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)

---

1 Flavone itself occurs almost pure as the mealy deposit found on the leaves of many plants of the primula class.Most natural dyestuffs are mordant dyestuffs and occur as glucosides in plants. Among these, the yellow dyestuffs which have been identified are mainly oxyderivatives of flavone¹ or flavanol.

Young Fustic contains a tri-oxy-flavanol termed [-] Fisetin. It is obtained from the wood of the sumach tree (rhus cotinus), a small tree indigenous to Southern Europe and the West Indian Islands. It is polygenetic and may be applied to the dyeing of wool. On account of the shades obtained from it lacking permanency it is little used.

Old Fustic is the wood of the tree chlorophora tinctoria, previously termed morus tinctoria. It is principally used in the dyeing of wool. Fustic consists mainly of two dyestuffs: Morin and Maclurin.

These are polygenetic, giving yellow shades with aluminium, tin and chrome, and olive with iron and copper mordants, although morin does not contain ortho-oxy-groups "(see p. 110).

The wood of the Osage Orange tree found in the United States behaves like Fustic in dyeing.

Patent Fustin is a colouring matter placed on the market which is mainly disazobenzene maclurin. It is obtained by extracting Old Fustic with boiling water, the solution filtered from the morin and its calcium salt, which separate on cooling, the filtrate neutralised with sodium carbonate and diazobenzene sulphate added until no further precipitation takes place; this precipitate is collected, washed, and sold in paste form. The disazobenzene maclurin has the following formula:[-]

Persian Berries consists of the dried unripe fruit of various species of rhamnus. It consists mainly of two flavanol derivatives, rhamnetin and rhamnazin, and small quantities of quercetin. It is employed for dyeing paper, leather, wool, in wool and calico printing for yellow shades, and for colouring foodstuffs.

Turmeric is contained in the tuber of curcuma tinctoria. It is now mainly employed for tinting and flavouring butter, cheese, confectionery, and for tinting lakes, fats and varnishes.
[-]

It is interesting as it is directly absorbed by cotton, and may be dyed in presence of a little acetic acid or alum. It is feeble to light and alkalis, acquiring a brownish red tint by treatment with the latter.

Annatto is obtained from the fleshy pulp surrounding the seeds of bixa orellana. It is mainly cultivated in Central America, in Cayenne, in Brazil, and in India, the latter giving the best seeds. The colouring matter is termed bixin C₂₈H₃₄O₅. Owing to the fugitive nature of the red and orange shades obtained by it, its employment is very limited.

It is used for colouring butter, cheese, margarine, soups, etc.

Quercitron Bark is the inner bark of a species of oak, quercus discolor; it is indigenous to the Central and Southern States of America. The epidermis or outer blackish bark is shaved off and the inner portion detached and ground or extracted. Although a very useful natural colouring matter, it has been considerably replaced by the cheaper Old Fustic. The colouring matter of quercitron consists of a tetraoxy flavanol termed quercetin.
[-]
It is a polygenetic dyestuff, giving shades very similar to fisetin.

The dyestuff is present in the bark partly as a glucoside, quercitrin. The glucoside quercitrin, like the dyestuff quercetin, is also polygenetic.

Flavin is a commercial preparation of quercitron bark. It is obtained by extracting the bark with water at 103°C. Two brands are known: yellow flavin, which consists mainly of quercitrin, and red flavin, which is mainly quercetin. The red flavin is obtained by ammoniacal extraction of the bark.

Patent Bark is obtained by boiling quercitron bark in powder with three times its weight of 5% sulphuric acid for about two hours; it is then filtered, washed and dried.

The preparations from quercitron bark are more powerfully tinctorial than the bark itself.

Weld consists of the plant reseda luteola; it contains mainly a textra-oxy-flavone luteolin.
[-]

It is polygenetic, and is employed to a small degree for the dyeing of all fibres, but mainly silk.

Dyer's Broom (Dyer's greenweed) is found in Central and Southern Europe, in Russian Asia, and is frequent in the greater part of England. It contains a flavone luteolin, the dyestuff of weld, and a cumarone genistein, a feeble polygenetic dyestuff, which has the following constitution:
[-]

The yellows obtained from Fustic, Quercitron Bark and Weld are similar in their application and fastness. In the latter respect they are good, but not equal to the best acid dyes as regards light-fastness. Nevertheless, Fustic and preparations of Quercitron Bark were largely used even before the European War occasioned a shortage of the competing artificial products.

Indian Yellow (Piuri) is obtained by heating fresh urine of cows fed upon mango leaves. The yellow mass that separates is pressed in cloths and is then rolled into balls. In this form it is the magnesium salt of euxanthinic acid [-] which on hydrolysis gives euxanthone [-]
It is mainly employed for colouring oil and water paints.

Cochineal consists of the dried insect coccus cacti, largely cultivated in Mexico. Carminic acid, the colouring matter of cochineal, probably has the empirical formula C₂₂H₂₂O₁₃. It crystallises from water or alcohol in red prisms; it darkens without melting at 130°C., and yields with alcoholic potash a monoand a dipotassium salt. On distillation with zinc dust naphthalene is obtained. It was formerly much used on a tin mordant for the scarlet or "grain" dyeing of wool and silk, but its use is now declining, as although fast to light it cannot compete with acid scarlets in other respects. It is used also as a tint for microscopic work, and for the colouring of foodstuffs, etc.

Lac Dye is produced by an insect coccits lacca or ficus. Stick lac used for dyeing is deep red or brown and contains about 70 per cent, of resin and 10 per cent, of dye. The lac dye is obtained by extracting the stick lac with soda carbonate solution, evaporating the extract and moulding the concentrated extract into cakes. For dyeing purposes the lac dye is treated with dilute hydrochloric acid to remove mineral matter. It is poly gene tic and is similar to cochineal, giving shades of good fastness to light but turned bluish by milling. Although faster to light than cochineal it has almost entirely gone out of use, while cochineal has remained in fairly extensive application. The main reason lor this is the greater insolubility of lac dye, which can only be overcome by more laborious preparation for dyeing, e.g., grinding with hydrochloric or oxalic acid.

Archil, Orchil and Cudbear are prepared from certain lichens, roccella tinctoria, lecanora tartarea etc., by submitting them to the action of oxygen (air) in presence of ammonia, or the plant is boiled with lime and water, allowed to settle, ammonia added and exposed to the air until dyestuff no longer separates. Archil appears in commerce as a pasty mass, and a reddish powder, cudbear.

The dyestuff can be obtained from Orcin by the rapid action of hydrogen peroxide and ammonia, or slowly by the action of air and ammonia. The products vary according to the time of action of the reagents.
[-]

The colouring matter (orceïn) dyes best from a neutral bath, but it may be dyed from slightly acid or alkaline baths. It is used for the dyeing of crimson on wool and silk, with or without mordants. The dye is largely used in conjunction with indigo for the dyeing of wool, being used both as a bottoming and as a topping colour. Although rather fugitive according to modern standards, it is still used for crimson in silk dyeing.

Catechu or cutch is a valuable dyestuff obtained from the dark red heart wood of Acacia, Areca, and Uncaria, growing in India. It is largely used for obtaining various shades of brown, olive, drab, grey, and black, and is employed for dyeing both animal and vegetable fibres.

In practice catechu is now seldom used, as a product "prepared cutch," which is obtained by heating catechu with aluminium sulphate, possesses greater colouring power.

Cutch is remarkable for the brown colour produced on cotton by chroming, the colour being very last to light, soap, alkali, acid, and also to bleaching liquor. Its use on wool is restricted owing to rendering the fibre harsh, but large quantities are used as a mordant in dyeing blacks on silk.

Catechin, one of the substances present in catechu, has the following constitution: [-]

Gambler catechu (or "Gambier"), in addition to catechin, contains a small amount of catechutannic acid, this substance being present in large quantities in the deep brown varieties of cutch. Catechutannic acid is said to be produced when catechin is heated to 110°C. It is a powerful tanning agent. Catechin is not precipitated by gelatin, and is not itself a tannin matter; it is, however, absorbed by hide, and there gradually passes into catechutannic acid.

Soluble Red Woods. - Brazil Wood, Peach Wood, Sapan Wood, and Lime Wood. These dyewoods are obtained from various species of caesalpinia. They have similar dyeing properties, and on account of the fugitive character of the colours they yield they are only used to a limited extent.

The woods contain the leuco dyestuff brasilin.
[-]

This oxidises in aqueous solution by exposure to air to the dyestuff Brasileïn.
[-]


Insoluble Red Woods. - Camwood, Barwood, and Sanderswood or Sandal Wood. The wood contains the dyestuff termed santalin, present to about 17% in sanderswood and 23% in barwood. These dye woods are obtained from certain species of pterocarpus and baphia.

They are principally used in wood-dyeing, in conjunction with other dyestuffs. Jn some combinations, e.g., with logwood, their inferior fastness does not reveal itself as might be imagined from separate tests. The dyestuff is polygenetic.

Logwood or Campeachywood consists of the heart wood of haematoxylon campechianum growing chiefly in Central America, Mexico, etc. The best sorts come from Mexico, Haiti, San Domingo, Honduras, Cuba, Jamaica, and Guadeloupe. There is also on the market an extract of the wood of variable strength. The principal use of logwood is for the production of blacks upon both animal and vegetable fibres, and it is often used for this purpose along with Fustic. It is a polygenetic dyestuff and gives, with an aluminium mordant, a blue colour; chrome, blue-black; iron, black; copper, green-black; and tin, violet.

The wood contains the leuco compound haematoxylin, and is therefore similar in constitution to brasilin.
[-]

By oxidation of haematoxylin, generally in ammoniacal solution by exposure to the air, haemateïn is produced, which probably has the following constitution:
[-]

Haeinateïn is converted into a colourless body by sulphurous acid or sodium bisulphite solution, readily soluble in water. No reduction, however, appears to occur, as on addition of an acid or on boiling, haematem is precipitated; also with zinc and acid, with stannous chloride and caustic soda, the solution is decolourised, but on standing the solution is again restored to its former tint.

Logwood used to be "aged." This process consists in piling the "chips" or "rasps" in a moist condition in a large airy chamber. The mass oxidises and the yellow wood turns dark reddish brown. At the present time this method is seldom used, as formerly iron was chiefly used as mordant, whereas bichromate is the mordant mainly used now for blacks, and the yellow chrome mordant oxidises the haematoxylin to haemateïn.

Logwood extract is still oxidised to obtain haemateïn, the oxidation being mainly done by means of sodium nitrite.

Commercial haemateïn crystals are among the best forms of logwood extract, and are usually much stronger in colouring power than solid logwood extract.

Woad is a dark clay-like product made from the leaves of the woad plant, isatis tinctoria. The plant is a biennial, indigenous to Europe, and has long been used for dyeing blue. The ancient Britons stained their skin blue with woad in time of war and in connection with certain religious observances. It was largely cultivated before the introduction of indigo from India. Woad is still grown in Lincolnshire and Huntingdon. The leaves are subjected to a fermentation process to prepare it for the market. Woad, although previously used for dyeing blue, is now only employed as a fermenting agent in the indigo-vat as used by the wooldyer. The vat so prepared is therefore termed the "woad-vat." Woad was considered to contain the same colouring matter as is present in the indigoferae. It is now known to be a distinct substance, which in most of its reactions resembles indoxylic acid.
---

(The student seeking further information on natural dyestuffs is recommended to consult the various articles by A. G. Perkin in Thorpe's Dictionary qf Applied Chemistry, also Die natürlichen Farbstoffe, Rupe.) The slight commercial importance of natural dyes as a class does not warrant further space being assigned to them in this book. All those dealt with above are still more or less in actual use, but only logwood, indigo, cutch and fustic are now of considerable importance in normal times. The famine in synthetic dyestuffs experienced by most nations except Germany during the European war, caused a transient revival of interest in the use of natural products for dyeing. This, however, is not likely to be repeated, as in most cases steps have been taken to prevent any future recurrence of shortage from the same cause.

The Chemistry of Dyestuff. Dyestuffs. XXV. Vat Dyestuffs.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)Under this group are included all those dyes which are insoluble in water, but can be applied to the. fibre through the intermediate production of a reduction or leuco compound which is soluble in dilute caustic alkali. The leuco compound is subsequently re-oxidised on the fibre to the original dyestuff. For this purpose a dyestuff must contain the ketonic or thioketonic group, which on reduction gives respectively a phenolic or tliiophenolic group capable of solution in alkali. The alkali compound of the phenol or thiophenol is taken up by the fibre and is then re-oxidised by air to the original ketone or thioketone. In many cases it is advisable also to treat the dyed material with some oxidising agent, such as bichrome or perborate, etc.

Indigo, which is the oldest and best-known member of this series, is very fast to light and to most other agents. It is faster however when dyed on wool than when dyed on cotton, wool probably having a more pronounced chemical affinity for indigo than cotton. The fastness to light of indigo is surpassed by many other vat dyes, but such fastness is by no means invariable in the class of vat dyestuffs.

The vat dyestufFs may be subdivided into three classes:
I. The Indigoid Vat Dyestuffs.
II. The Anthraquinone Vat dyestuffs.
III. The Sulphurised Vat Dyestuffs.

No really sharp class distinction, however, can be drawn in the case of certain dyes of these series.

The Indigoid Class may be applied to wool as their leuco compounds are soluble in very dilute alkali. The amount of alkali permissible without risk of injury to the wool must be exceeded in many cases however, and various "restrainers" have been added in dyeing, e.g., glue, glucose, formaldehyde, and soluble oils.

The Anthraquinone Class are mainly in use for cotton dyeing, and are not generally applied to wool because they usually require too much caustic alkali to dissolve their leuco compounds. They may, however, in certain cases be applied to wool, although great difficulties have to be overcome.

The Sulphurised Class are also more important for cotton dyeing.


The Indigoid Class. - The class of indigo derivatives is characterised by the presence of one or two fivemembered rings, in which a ketonic group is present along with either carbon, nitrogen, or sulphur, one of the carbon atoms of this ring being combined by a double bond to a similar carbon or to a ring component carbon atom, as for example to anthracene or naphthalene, provided there is a ketonic group ortho to the double-bonded carbon. Several types are possible therefore as represented by the following chromogenes:



When synthetic indigo was first placed on the market many virtues were claimed by dyers for natural indigo as compared with the chemically pure synthetic product. The valuable red bloom on indigo navies is more easily obtained with the older dyes, and this was attributed to the natural indigo containing indirubin (indigo red). The natural indigo also contains small amounts of indigo brown, indiglutin, etc. It has been shown, however, that indirubin, on reduction in the indigo vat, gives indoxyl which oxidises later in presence of air, giving indigotin or indigo blue. The indiglutin, a degradation product of indigo, is perhaps the most important impurity apart from clay andgums which may exert a colloidal influence. Owing to the varying quantities of substances other than indigotin present in natural indigo, the shade produced from it varies with different samples, and also varies during dyeing from the same vat. The shade produced by synthetic indigo is always the same, if the same percentage of dye is fixed on the fibre, and the same method of dyeing is employed. The shade of indigo varies, however, with the manner of application and the after-treatment. For example, steaming the dyed goods for a short time makes the blue a little more violet, and also increases its fastness against light.

Indigo (indigotin) is present in both plant and animal life in the form of its glucoside indican. This glucoside is formed in small quantity by a process of deassimilation in the stalk and leaves of indigofera tinctoria and indigofera sumatrana, which are cultivated chiefly in India and Java. The leaf of the indigo plant contains, on an average, about 0,5 per cent, of colouring matter. Two crops are gathered from the same plants each year, the second crop some two or three months after the first. The cut plant is put into vats and extracted with water, the temperature of which is about 30° to 35°C.; the length of time required for extraction varies from nine to fourteen hours. Towards the end of the extraction marsh gas and hydrogen are evolved, and about this period the fermentation diminishes and the liquid subsides. The liquid is then run off into the beating vats, in which oxygen from the air acts as the oxidising agent and precipitates the indigo from the vat. It is then filtered, boiled with water, pressed, dried in the shade, and cut into blocks.

The amount of indigotin present in natural .indigo varies very widely. Java indigo usually contains most, as a rule 70 per cent, and upwards, while good Bengal indigo contains 60 to 65 per cent, and Madras indigo 30 to 40 per cent. As much as 10 per cent, of indirubin is found in some commercial samples.

The shortage of artificial indigo, due to the war, has done much to revive indigo cultivation again, which dwindled rapidly after the synthetic product appeared on the market.

The Badische Anilin und Sodafabrik manufactured indigo in 1897 by the Heumami method which consists in the fusion of phenylglycine with caustic soda, followed by oxidation of the alkali melt, after solution in water, with air.

Phenylglycine by loss of water gives indoxyl thus: [-]
indoxyl on oxidation, e.g., with air, gives indigo: [-]

The yield by this method was extremely poor, but by replacing the phenylglycine by its ortho carboxylic acid a fairly good yield is obtained. The phenylglycine-ocarboxylic acid is obtained either from naphthalene or from o-chlorobenzoic acid Naphthalene is oxidised by sulphuric acid in presence of mercury to furnish phthalic anhydride, and the latter is converted by ammonia into phthalimide [-], which by treatment with sodium hypochlorite gives anthranilic acid [-], this being converted into phenylglycine-o-carboxylic acid by condensation with chloroacetic acid. The ochlorobenzoic acid produces the same compound by heating with glycine in presence of copper salts.

A better yield of indigo is obtained by condensation of phenylglycine by heating with sodamide and caustic soda, or by heating methylanthranilic acid with sodamide and caustic soda. The use of sodamide for indigo manufacture was discovered by the Deutsche Gold u. Silberscheide Anstalt and purchased by Meister, Lucius and Bruning. The sodamide may be produced in the reaction mixture of sodium and the sodium salt of phenylglycine by action of ammonia.

Sodium anilide (C₆H₅NHNa) also finds application in the indigo synthesis, this compound increasing the yield of indigo similarly to sodamide (S. C. I.).

Whatever method is employed it is essential to carry out the condensation in absence of air to prevent
the formation of isatin [-], an oxidation product of indigo, which causes the formation of indirubin.

Indigotin is also placed on the market in a reduced form, Indigo White, which may be prepared from indigo by reduction with iron powder and caustic soda, or by glucose and caustic soda, such as Indigo White BASF (B.) or Indigo MLB/W (M.).

When indigo is reduced in the vat two atoms of hydrogen are taken up by the molecule of dyestuff, the following compound [-] probably being produced. This transforms into Indigo White [-] the leuco compound dissolving in the alkali present to give a yellowish green vat.

In order that synthetic indigo may be readily reduced it is placed on the market in as fine a state as possible, and in many cases compounds are added to preserve the indigo in colloidal form during oxidation, e.g., benzylaniline sulphonic acid (B., 1912).

Indigo Salt T (K.) is obtained by the action of dilute caustic soda upon a solution of ortho-nitrobenzaldehyde in acetone.
[-]

Indigo, when pure, is a crystalline substance with a coppery hue subliming to give violet vapours on heating. This property of sublimation is common to indigoid vat dyestuffs, and is useful as a means of distinguishing from anthraquinone and sulphurised vat dyestuffs which with the exception of Anthraflavone (B.) do not sublime. Another means of distinguishing lies in the different coloured leuco compounds obtained in the vat on reduction. While insoluble in water and common solvents, the indigoids are, generally speaking, more easily dissolved than anthraquinone and sulphurised vat dyestuffs. Thus indigo itself is soluble in boiling glacial acetic acid, pyridine, phenol, benzaldehyde, nitrobenzene, etc., but only sparingly soluble in any of these in the cold.

On dissolving indigo in concentrated sulphuric acid at 70°C. it becomes converted into a mono-sul phonic acid ( SO₃H para to NH ). This, as sodium salt, constitutes the commercial red or purple Indigo Extract. The disulphonic acid obtained by longer sulphonation is more used - Indigo Carmine. It finds some use as an acid dye of no particular fastness.

Indigo is readily converted into isatin by treatment with oxidising agents, e.g., nitric acid, chromic acid, etc. This is made use of technically in discharging indigo dyed cloth, and in the estimation of indigo (as sulphonate) by titration with permanganate.

[The common facts relating to the chemistry of indigo are to be found in all organic chemistry textbooks, and for that reason a somewhat curtailed treatment has been accorded here.]


Derivatives of Indigo. - The halogen derivatives are perhaps the most important. These may be produced from halogen compounds or the indigo may be halogenated, the halogenation being carried out in a solution or in presence of nitrobenzene, dichlorobenzene, concentrated sulphuric acid or chlorosulphonic acid. By progressive bromination of indigo it is possible to introduce from one to six atoms of bromine into the indigo molecule.

The indigo derivatives are named according to the positions of the groups, the positions being numbered as follows: [-]

Bromine first enters into position 5 forming a monoor di-bromo-derivative continuing through the following series: 55'7 to 55'77', finally to 5'57'74' and 5'57'74'4. The 66' compound cannot be obtained by bromination of indigo, but is produced from 4-bromo-2-amino-benzoic acid. The 66' dibromo-indigo was found by Friedlaender to be one of the dyestuffs present in the shell-fish murex brandaris, from which Tyrian Purple was obtained by the ancients.

The chloro indigos are obtained from the halogen derivatives of phenylglycine.

The halogenated indigos are brighter in shade and faster to bleaching agents than indigo itself, but by increasing the substitution the relative tinctorial power is decreased.

Homologues of indigo do not appear to have any special value; a 77' dimethyl indigo, Indigo MLB/T (M.) or Indigo pure BASF/G (B.), is, however, manufactured. It dyes greener shades, which are faster to chlorine than indigo.

Amino derivatives of indigo give brown vat dyes; a brominated diamino-indigo, Ciba Brown R (S.C.I.), is on the market. It dyes cotton and wool reddish brown, which is fast to light and washing but not to bleaching.

Naphthalene indigos have been obtained from aand β-naphthylamine; they are green dyestuffs, but are comparatively fugitive and therefore are of little value. The beta-compound, however, gives valuable vat dyes on brominatiou. Ciba Green G (S.C.I.) and Helindone Green G (M.) belong to this class.
[-]

The naphthalene indigos show less disposition to sublime on heating than the simple indigos. Ciba Green G when heated gives some reddish violet vapours, but most of the dyestuffs carbonise without subliming.

Indigo Yellow 3G (S.C.I.) is prepared by heating indigo with benzoyl chloride in nitrobenzene solution in presence of copper powder. It gives a bluish-red vat on alkaline reduction. It is of particular interest, since it may be dyed along with indigo from the same vat giving uniform green shades. Generally a mixture of indigoid dyes gives uneven shades due to unequal affinity of these dyes for the fibre and the special amounts of alkali and particular temperatures required. It has most probably the following constitution:
[-]

Most natural indigos contain Indirubin. This compound is obtained by condensation of isatin with indoxyl, [-] and is also obtained during the production of synthetic indigo when air is admitted to the caustic melt. Indirubin, when vatted, is to a large extent converted into indigo-blue, this is accompanied with loss of dyestuff. The amount of indirubin dyed and fixed on wool is therefore small and also it is of little value, as it gives shades loose to washing. Certain derivatives of indirubin are sufficiently fast, however, to be employed commercially as vat dyestuffs, notably halogen derivatives. By bromination the fastness to washing is improved. Ciba Heliotrope B (S.C.I.) is a tetrabrominated indirubin giving a yellowish olive vat.

In 1905 Friedlaender discovered Thioindigo Red B (K.), this being the first of a large series of vat dyes. It is similar in constitution to indigo, the NH group being replaced by sulphur. Its derivatives are named similarly to those of indigo.
[-]

It is termed bisthionaphtheneindigo and is obtained from thiosalicylic acid, which, on heating with sodium chloroacetate, gives phenylthioglycol-ortho-carboxylic acid. This, on heating, gives thioindoxyl, which may be oxidised to Thioindigo Red (K.) (cf. indigo synthesis).
[-]

Thioindoxyl on oxidation, preferably with potassium ferricyanide, gives Thioindigo Red.

Many derivatives of Thioindigo Red have been prepared, introducing a variety of shades.

Helindone Grey BR (M.) is a dichloro-diamidothioindigo dyeing from a yellow vat.

Helindone Violet (M.) is dichlorodiinethyl-dimethoxy-thioindigo.

Helindone Scarlet S (M.) is diethylthio-oxy-thioindigo.

Ciba Bordeaux B (S.C.I.) is 5.S'-dibrom-bisthionaphtheneindigo. It forms a yellowish orange vat on reduction.

By the condensation of the thionaphthene ring with the indoxyl or indol ring a variety of vat dyes are obtained, these being the thionaphthene-indol indigos; the combination of the two ring systems may be at the 2 or 3 positions both in the indol ring and the thionaphthene ring. Oxythionaphthene or its derivatives is condensed with isatin or its derivatives, or with alpha-isatin derivatives.

One of the most important is Ciba Red G (S.C.I.) or Thioindigo Scarlet G (K.), which is obtained by the condensation of isatin with alpha-oxy-thionaphthene followed by bromination.
[-]

It may be termed 2-thionaphthene-5.7-dibrom-3-indol indigo. It dyes from a pale yellow vat and is a valuable dyestuff, being fast to light and bleaching.

Other dyestuffs of this series are:

Ciba Violet B (S.C.I.) or tribrom-2-thioriaphthene-2-indol indigo.

Ciba Grey G (S.C.I.) or brom-2-thionaphthene-2-indol indigo.

Acenaphthoquinone also condenses with indoxyl or oxythionaphthene or their derivatives to produce vat dyes. One of good fastness to almost all agencies is Ciba Scarlet G (S.C.I.) or 2-thionaphthene-acenaphthene indigo.
[-]

Vat dyes may also be obtained by the condensation of isatin or its brom derivatives with naphthol or anthranol or certain derivatives of these compounds.

Alizarin Indigo 3R (By.) or 2-naphthalene-2-indol indigo gives a yellow vat on reduction. It is obtained when dibromisatin is condensed in benzene solution with alphα-naphthol.

Helindone Blue 3GN (M.) is obtained by the condensation of oxyanthranol with isatin anilide.
[-]

Alizarin Indigo G (By.) is a brominated 2-anthracene-2-indol indigo.


Anthraquinone Vat Dyes.

The dyes of this series may be roughly divided into three types: a ring system in which nitrogen is absent, a ring system in which nitrogen is present (mainly dyes obtainable from amino anthraquinones), and sulphurisation products of anthraquinone and its derivatives. Many of these dyes are particularly interesting on account of their high molecular weight and their complex structural formula. Many coloured bodies derived from anthraquinone and such of its derivatives as furnish a leuco body in the hydrosulphite vat, do not possess the necessary affinity for the fibre.

The simpler vat dyestuffs of this series may be compared with the parent body anthraquinone; this body is insoluble in alkalis, but may be reduced by alkaline reducing agents giving oxanthranol.
[-]

The oxanthranol is soluble in alkalis, forming a blood red solution; this compound on exposure to air gives the original quinone again. Compounds similar to this, if of sufficient tinctorial power, may therefore be used as vat dyes.

Anthraflavone G (B.) is a stilbene derivative obtained by heating β-methylanthraquinone with alcoholic potash from 150 to 170°C. It dyes cotton a fast greenish yellow from a dark reddish-brown vat.
[-]

Indanthrene Gold Orange G (B.) is obtained from 2.2'-dimethyl-l.1'-dianthraquinonyl by heating with or without dehydrating agents. It gives a magenta coloured vat.
[-]

In this and certain other formulae for vat dyes the quinone form =O is written instead of the ketonic -CO- in order to simplify complex formula.

Indanthrene Gold Orange R (B.) is a chloro derivative of the above, and Indanthrene Scarlet G (B.) a bromo derivative of it; it gives a reddish-violet vat.

Indanthrene Dark Blue BO (B.) is another example of the peculiar complex condensation that may be carried out with anthracene derivatives.

Benzanthrone, obtained by heating anthranol, glycerine and sulphuric acid, is heated with caustic potash, whereby two molecules condense together.
[-]

Indanthrene Green B (B.) is a nitration product of the previous dyestuff; it is particularly interesting, since by the action of oxidising agents upon cotton dyed with this colour a fast black is obtained, namely, Indanthrene Black B (B.).

Indanthrene Violet R extra (B.) is isomeric with Indanthrene Dark Blue BO (B.); it is obtained by a caustic potash melt of halogen derivatives of benzanthrone.
[-]
It was found at the Bayer Farben Fabrik that simpler compounds, benzoylated oxyor amidoanthraquinones, had the properties of vat dyes.

Algol Yellow WG (By.) is benzoyl-1-amidoanthrrquinone.

Algol Scarlet G (By.) is benzoyl-l-amido-4-methoxy anthraquinone.

Algol Red 5G (By.) is dibenzoyl-1.4-diamidoanthraquinone.

Algol Red R extra (By.) is dibenzoyl-1.5-diamido-8-oxy anthraquinone, and gives a red vat.

The first two members of the anthraquinone vat series to be discovered contain nitrogen, and were obtained from β-amidoanthraquinone by fusion with caustic alkali. At temperatures from 200° to 250°C. a blue dye is obtained, and at 330°-350°C. a yellow one. These two dyes were discovered in 1901 by R. Bohn at the Badische Anilin imd Sodafabrik.

Indanthrene Blue R (B.) is one of the oldest of the anthraquinone vat dyes, and is still the most important and the most largely used of these colours. It is obtained by heating β-amidoanthraquinone with caustic potash and potassium nitrate. The melt is dissolved in water and the dyestuff which separates is filtered off. It is purified by reduction to the leuco form and separation of the sodium salt from caustic soda solution, this being then well washed with alkaline bisulphite solution.
[-]

It would be termed as a leuco-azine N-dihydro-1.2-1'.2'-anthraquinone azine. It dyes bright blue shades from a dark blue vat.

Algol Blue K (By.) is the N-dimethyl derivative of the above compound.

Algol Blue 3G (By.) is 4.4'-dioxyindanthrene.

Indanthrene Yellow G. (B.) is obtained similarly to Indanthrene Blue R, except that the condensation temperature is much higher. It may also be obtained by heating β-amidoanthraquinone with antimony pentachloride in nitrobenzene solution.
[-]

It dyes bright yellow shades from a dark bluish violet vat.

Helindone Yellow 3GN (M.) is 2.2'-dianthraquinonyl urea.

Imides of the anthraquinone series form a large class of vat dyes of which the following are a few examples.

Algol Red B (By.) is β-anthraquinone-α-anthra-N-methylpyridonamine.
[-]

Indanthrene Bordeaux B (B.) is dichloro-di-aanthraquinonyl-2.7-diamido-anthraquinone.
[-]

Algol Bordeaux 3B (By.) is 4.4'-dimethoxy-di-α-anthraquinonyl-2.6-diamido-anthraquinone.


Vat dyes of the acridone series. - These dyestuffs are obtained by condensing chloro anthraquinone derivatives with anthranilic acid.

Indanthrene Red BN extra (B.) is an anthraquinonenaphthacridone.
[-]

Indanthrene Violet RN extra (B.) is an anthraquinonediacridone.
[-]


Sulphurised Vat Dyes. - These are obtained from anthracene and many of its derivatives or condensation products by heating with sulphur to a high temperature.

Indanthrene Olive G (B.) is produced by heating one part of anthracene (96 to 98 %) with three parts of sulphur to 250°C. until sulphuretted hydrogen is no longer given off. It gives a dark violet vat which dyes olive shades fast to light and washing.

Cibanone Blue 3G (S.C.I.) is a sulphur melt product of methylbenzanthrone.

Cibanone Black B (S.C.I.), Cibanone Green B, Cibanone Orange R, and Cibanone Yellow R (S.C.I.) are all vat dyes of this series.

By the condensation of indophenols of carbazol, or N-substi tuted carbazols with sodium poly sulphide, vat colours are obtained.

Hydron Blue R (C.) is obtained from the indopbenol of carbazol and sodium polysulphide. It is one of the vat dyes most used on cotton.
[-]


The addition of copper salts to the melt gives Indocarbon S (C.).


-(For reference:
Barnett, "Chemistry of Vat Dyes," J. Soc. Dyers, 1913, p. 183.
Vlies, "Recent Progress in Colouring Matters," J. Soc. Dyers, 1913, p. 316; 1914, pp. 22 and 29.)

The Chemistry of Dyestuff. Dyestuffs. XXIV. Sulphide Dyestuffs.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)The first member of this series, Cachou de Laval, an impure and unstable brown dyestuff, was prepared in 1873 by Croissant and Bretonniere by heating vegetable substances, such as sawdust, starch, straw, along with sodium hydroxide and sulphur or sodium sulphide and sulphur. Later it was found that animal and human excrement also gave similar results by fusion with sodium sulphide and sulphur. Cachou de Laval, it was found, acted as a mordant for fixing the basic dyestuffs and also giving different shades (saddenings) by after-treatment with iron or copper mordanting salts. The property _of fixing basic dyestuffs is a property possessed by nearly all sulphide dyestuffs, many also having the power of fixing acid and direct cotton dyestuffs, properties of great value in cotton dyeing.

In 1893. R. Vidal produced a sulphide black, Vidal Black (P.), from para-amido-phenol, to which he gave the following formula: [-] and at about the same period R. Bohn discovered Fast Black B (B.), which was obtained from 1.8-dinitronaphthalene. This was the opening of the sulphide era, and during the following ten years almost every organic substance was subjected to sulphide condensation. The varying proportions of sulphur to sodium sulphide, the proportion of the sodium polysulphide produced, the reaction temperature, and the aftertreatment of the reaction mass, all play important parts.

The constitution of the sulphide dyestuffs is not yet known. They appear to be thiazine derivatives or similarly constituted polysulphides, possessing the property of dissolving in sodium sulphide solution, the dyestuff being converted by alkaline reduction into the leuco form, and in this form it is absorbed by vegetable fibres and re-oxidised on the fibre, this being aided in some cases by after-treatment with chrome or copper salts.

The sulphide, unlike the vat dyes, re-oxidise to some extent during dyeing.

The sulphide dyes are very insoluble amorphous bodies, giving on reduction thio-oxy derivatives, which are soluble in alkali. Green and Meyenberg found that by oxidising a mixture of a para-diamine or a paraamido-phenol and a large excess of sodium thiosulphate with cold potassium bichromate, a dior tetra-thiosulphonic acid is obtained.
[-]

On oxidising either of these compounds with bichromate along with amines, amido-phenols, etc., indamine sulphonic acids are obtained which, on boiling with dilute mineral acids, give products of this series. This method of preparation points to the presence of the thiazine ring in these dyestuffs.

There are practically two methods employed for the preparation of these dyes:
I. Baking.
II. Boiling under reflux condenser.

The latter favours the production of purer products and minimises the quantity of free sulphur in the final product. The dyes are separated by acid precipitation or air oxidation, the latter method yielding the better product.

Sulphide Yellows. - These dyestuffs are generally obtained from meta-toluylene-diamine, or its derivatives, by heating with sodium poly sulphide. The lower the temperature at which the condensation takes place, as a rule, the brighter is the colour of the dyestuff that is produced. In the case of the yellow sulphide dyestuffs the reaction products are often too insoluble to be used directly in the dyebath. By heating with sodium sulphide at about 120° to l25°C. the compounds are rendered more soluble, and may then be evaporated to a solid product or they may be precipitated by acid.

Dehydrothiotoluidine also gives yellows by a sulphide melt treatment, the shade being improved by addition of benzidine or its homologues to the melt.

By raising the temperature for the condensation of m-toluylene-diamine with sulphur, the colour of the final product tends to become more orange or brown.

Meta-toluylene-diamihe is employed for the production of Immedial Yellow D, Immedial Orange C (C.) and Thion Yellow G (K.). Thiourea derivatives of the above substance are employed for the production of Kryogene Yellow (B.) with or without the addition of benzidine. Para-phenylene-diamine, along with paraamido acetanilide and benzidine, also gives yellow to bronze sulphide dyestuffs, e.g., Thiophor Yellow Bronze G (J.).

Sulphide Browns. - Of these dyestuffs only a few are of real commercial value, in spite of the immense number of organic compounds from which they may be obtained.

Kryogene Brown (B.) is obtained from 1.8-dinitronaphthalene by treatment with sodium bisulphite, followed by condensation by means of sulphur and sodium sulphide.

Thional Brown (S.) results when certain arylamido derivatives of β-naphthoquinone are condensed at 240° to 280°C. by treatment with sodium polysulphides.

Thiocatechine (P.) is obtained by condensing one part of acetyl-para-phenylene-diamine with two parts of sulphur at 200° to 250°C. As soon as the violent reaction has ended and sulphuretted hydrogen is no longer given off, the mass is allowed to cool. It is soluble in sodium sulphide and dyes cotton catechu brown shades.

Sulphide Reds. Red is the only colour that is not satisfactorily represented in the sulphide dyestuffs. The red dyestuffs of the azine series, when heated with polysulphide, give those sulphide dyes which most nearly approach to red. Safranine is the one most commonly used. The introduction of copper, nickel and cobalt salts to the melts also tends to produce redder sulphide colours.

Immedial Bordeaux (C.) is obtained from a simple azine, amido-oxyphenazine, by a sulphide melt process.

Sulphide Greens. Many of the melts which give black sulphide dyestuffs give green dyestuffs when copper salts are added also. Two of the most important intermediate products for the production of these colours are l-phenylamido-4-p-oxyphenylamidonaphthalene-8-sulphonic acid [-] and 4-p-oxyphenylamido-l-amidonaphthalene sulphonic acid [-]

Sulphide Blues. - The blues are mainly obtained from indophenols. These compounds are easily produced by condensation of para-diamines, or para-amidophenols, with amines or phenols. Both benzene and naphthalene derivatives are largely used for this class. Para-oxypara-amidodiphenylamine obtained from aniline and para-amidophenol by oxidation with bichromate, or by oxidation of a mixture of phenol and para-phenylenediamine, and also para-phenylamino-para-oxy-diphenylamine obtained from diphenylamine and para-nitrosophenol, are both extensively used for the manufacture of sulphide blues.

Immedial Sky Blue (C.) is obtained by condensing dimethyl-p-amido-p-oxydiphenylamine with sodium polysulphide at 110° to 115°C. by heating under reflux condenser. Its probable formula is [-]


Sulphide Blacks. - A large variety of nitro-compounds may be used for sulphide black melts. 2.4dinitrophenol, 1.5 and 1.8or the mixture of these two dinitronaphthalenes, 1.5-dinitroanthraquinone, dinitrodiphenylamine, together with their oxy and chloro derivatives or corresponding derivatives of diphenylamine, are the main intermediate compounds used for sulphide blacks.

The preparation of sulphide blacks may be best understood, however, from actual examples.

Sulphur Black T (Ber.). 85 parts of crystallised sodium sulphide are dissolved in 100 parts of water; 30 parts of sulphur are dissolved in the above solution by heating on the water bath. To the above solution 20 parts of 2.4-dinitrophenol are gradually added and the reaction mass heated for 20 hours under reflux condenser. The solution is then tested by spotting a drop on filter paper; if the reaction is complete no yellow colour will be seen at the edge of the spot. If a yellow edge is shown boiling is continued until it is no longer produced. The dyestuff is obtained from this solution by precipitation by means of acid or aeration.

Immedial Black V (C.). 20 parts of 2.4-dinitro4'-oxy-diphenylamine are added slowly to a solution of 16 parts of sulphur in 44 parts of crystallised sodium sulphide. The reaction mass is now heated, in an oil bath, to 140°C. during five hours under reflux condenser. The solution becomes deep blue-black in colour, and about this stage a vigorous evolution of sulphuretted hydrogen takes place. As soon as this has subsided, the solution is diluted and air drawn or blown through it until no more dye is precipitated; it is then filtered, washed, and dried.
Unless carefully manufactured, sulphide dyes, especially blacks and browns, are liable to contain sulphur in a loosely combined form, which oxidises readily to free sulphuric acid, e.g., in the drying stove, or after dyeing when goods are subjected to heat and moisture, thus tendering the fabric. Alkaline impregnation of cloth has done much to diminish tendering from this cause, but still more is due to improvements in the methods of dye manufacture, e.g., the use of air precipitation instead of acid, the accurate adjustment of melt quantities and the replacement of baking methods by condensation in solution. The sulphide dyestuffs find their chief use on vegetable fibres, as the hot alkaline bath, from which they are dyed, acts unfavourably on animal fibres and tissues. A noteworthy fact in connection with the sulphide dyes, which in most respects possesses considerable fastness, is their small resistance to hypochlorites.

The following are among the best known brands of sulphide dyestuffs: Auronal (W-t-M.), Cross Dye (R.H.), Eclipse (G.), Immedial (C.), Katigen (By.), Kryogene (B.), Pyrogene (S.C.I.), Sulphur (Ber.), Thiogene (M.), Thion (K.), Thional (S.), Thionol (Lev.), Thiophor (J.), Thioxine (G.E.), Vidal (P.).

The Chemistry of Dyestuff. Dyestuffs. XXIII. Oxyketone Dyestuffs.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)The dyestuffs of this series belong to the mordant class and are mainly used in conjunction with a metallic mordant.

One of the simplest dyes of this series is Alizarin Yellow C, which is gallacetophenone. It is prepared by heating acetic acid with pyrogallol in presence of zinc chloride.
[-]

Alizarin Yellow A is the corresponding trioxy benzophenone. This dyes redder shades than the above compound.

Dyestuffs are obtained by careful oxidation of oxybenzoic acids. Galloflavin W (B.) is obtained by oxidation of gallic acid in alcoholic potash solution with air, followed by treatment of the product with acid.

The simplest of the diketo-dyes of this series is Alizarin Black WR, SW, SWR, etc. (B.) is 1.2-dioxy-5.8-naphthoquinone, and is prepared from crude diuitronaphthalene (1.5 and 1.8-) by heating with a solution of sulphur sesquioxide in sulphuric acid solution, followed by hydrolysis of the 1.2-amino-oxy-α-naphthoquinone-imine by boiling with dilute acid. The insoluble Naphthazarin is converted into a water-soluble product by addition of sodium bisulphite.
[-]

One of the oldest and best known members of this series is Alizarin which is present in madder root, which contains from two to four per cent, as a glucoside. It is a good example of those colouring matters which dye only with the aid of a mordant, and which yield various colours with different mordants (polygenetic dyes). The use of a mordant is obligatory, alizarin itself having no affinity for vegetable fibres, and only imparting a fugitive orange brown colour to animal fibres. Its compound with alumina is red, with stannous oxide orange, with chromic oxide brownish violet, with ferrous oxide blackish violet, with ferric oxide brownish black. These colours when produced on textile fibres are fast to light, washing, and milling, etc., the fastness however varying somewhat with the mordant used.

In 1869 Perkin, and also Graebe and Liebermann, produced alizarin from anthraquinone by sulphonation with fuming sulphuric acid, followed by caustic fusion in presence of an oxidising agent. In. the manufacture of alizarin it is only necessary to obtain anthraquinoneβ-sulphonic acid, since this compound on heating with caustic soda gives alizarin.
[-]

Nascent hydrogen is obtained during the reaction; this reduces the alizarin to a leuco compound and also causes a poor yield of the dyestuff. The oxidising agent is added to prevent nascent hydrogen from being formed, thus obtaining a good yield of the dyestuff.
[-]

Alizarin P (B. A.), VI (B.), IE (By.), No. I (M.), etc., is obtained when anthraquinone-β-sulphonic acid is heated with alkali, etc. It is however usually obtained along with other oxy derivatives of anthraquinone. During the sulphonation of anthraquinone small quantities of disulphonic acid are also obtained, these giving trioxy anthraquinones by alkali fusion.

By further sulphonation of anthraquinone a mixture of 2.6and 2. 7-anthraquinone sulphonic acids is obtained These compounds may be separated by crystallisation of their sodium salts. They give, on fusing with alkali, Flavopurpurin or Alizarin YCA (B.A.), CH, RG (B.), VG, XG (By.), etc. [-] and Anthra- or Iso-purpurin or Alizarin SO (B.A.), SX, GD (B.), RF, WR (By.), etc.
[-]

Purpurin (B.A.) (B.), or 1.2.4-trioxyanthraquinone is obtained by oxidation of alizarin in sulphuric acid solution by manganese dioxide.

Alizarin Bordeaux B (By.), etc., is obtained by Oxidation of alizarin with strong fuming sulphuric acid, giving a sulphuric ester which is hydrolysed by strong sulphuric acid (80%). The aluminium lake is bordeaux and the chrome lake violet blue.
[-]

Alizarin Cyanin R, 2R, NS, WRR (By.), etc., is obtained by oxidation of alizarin bordeaux with manganese dioxide similarly to the oxidation of alizarin to purpurin. This dyestuff gives a violet aluminium lake and a blue chrome lake.
[-]

1.5-dinitroanthraquinone similarly to 1.5-dinitromiphthalene gives on .treatment with a solution of sulphur sesquioxide an oxy-imido compound which, on hydrolysis with ordinary sulphuric acid, gives the hexahydroxyanthraquinone shown above.

By increasing the number of oxy groups in anthraquinone, the polygenetic nature of the resulting dyes becomes gradually diminished.

Nearly all of the above dyestuffs of the anthraquinone series are converted into acid mordant dyes by sulphonation with fuming sulphuric acid.

Alizarin Red S (By.), WS (M.), etc., Alizarin Powder SA, Alizarin Carmine (B.A.) is the product obtained when alizarin is sulphonated with fuming sulphuric acid at 170°C.
[-]

Erweco Alizarin Acid Red BS (W.) is a mixture of the sodium salts of alizarin 5and 8-monosulphonic acids. It is obtained by sulphonation of alizarin with fuming sulphuric acid in presence of mercury. Alizarin 3.5and alizarin 3.8-disulphonic acids are obtained, which, on hydrolysis, give monosulphonic acids.

Anthracene Brown (R.H.), (B.A.), W, WR (B.G., etc.), or Alizarin Brown R, W, H (M.), etc., or 1.2.3-trioxyanthraquinone is obtained by condensation of benzoic and gallic acids in sulphuric acid solution. It is always associated with some 1.2.3.5.6.7-hexa-oxyanthraquinone or rufigallol, which is also known as Anthracene Brown SW (B.) or Alizarin Brown R, S (M.), etc.

Alizarine Orange AO, AOP (B.A.), A, W, SW (B.), N (M.), etc., is obtained by the action of nitric acid upon alizarin in suspension in nitrobenzol, acetic acid, ligroin, or sulphuric acid, to which boric acid is added.
[-]

If the alizarin is benzoylated before nitration, the nitro group enters the alpha position, and on hydrolysis and reduction with sodium sulphide gives Alizarin Garnet (M.).
[-]

Alizarin Blue S, SW (B.), (By.), etc., is the sodium bisulphite compound of Alizarin Blue ABI (B.A.), X, R, WX (B.), F (M.), GG, XA, WA (By.), etc,
[-]

It is obtained by the action of glycerin, nitroalizarin, and amidoalizurin in sulphuric acid solution, viz., by the application of Skraup's reaction to nitro derivatives of the anthraquinone dyes.

Alizarin Green S (M.) is a similar substance obtained from α-amidoalizarin, Alizarin Green X (B.) and Alizarin Indigo Blue (B.) are corresponding compounds obtained from 3-nitro-Alizarin Bordeaux, and treatment of this compound with sulphuric acid at 200°C. finally converting into bisulphite compounds, while Alizarin Black P (M.) is obtained from 3-nitroflavopurpurin.

On account of the insolubility of these dyes they are marketed as 20 % pastes. Soluble powders are obtained by formation of an addition product with two molecules of sodium bisulphite.

Most of the following derivatives of aminoanthraquiuones are after-chrome mordant dyes; they may, however, be applied also as simple acid colours.

Alizarin Irisol D, R (By.), etc., is obtained by heating p-toluidine with quinizarin (1.4-dioxy anthraquinone) followed by sulphonation.
[-]

Anthraquinone Violet (B.) is obtained from 1.5diamidoanthraquinone by heating with p-toluidine followed by sulphonation of the product thus obtained.

Alizarin Sky Blue B (By.) is obtained by condensation of p-toluidine with dibrom-α-amidoanthraquinone followed by sulphonation.
[-]

Alizarin Saphirol B (By.) is obtained by sulphonation of 1.5-dioxyanthraquinone (Anthrarufin) followed by nitration and reduction.
[-]

Various brands of this dye are used in dyeing mode shades on wool, which are very fast so long as chlorides (NaCl) are absent.

Alizarin Cyanin Green E, G (By.), etc., is obtained by sulphonation of the product produced by heating quinizarin with p-toluidine.

Acid Alizarin Green G (M.) results when dinitroanthrachrysone disulphonic acid is reduced in alkaline solution with sodium sulphide.
[-]


- See also "The Present Condition of the Chemistry of Anthraquinone," by R. K. Schmidt, Jour. Soc. Chem. Ind. 1914, p. 1039.

The Chemistry of Dyestuff. Dyestuffs. XXII. Azine, Oxazine and Thiazine Dyestuffs.

A Manual for Students of Chemistry and Dyeing
By
M. Fort, M.Sc. (Leeds) Late Lecturer in Dyeing in the Bradford Technical College and L. L. Lloyd, Ph.D. (Bern) Lecturer in Organic and Technical Chemistry in the Bradford Technical College
Cambridge: at the University Press 1919
(First edition 1917, reprinted 1919)These dyestuffs differ from each other very little in general properties. The commercial products are mainly basic dyestuffs.

They all give leuco compounds on reduction, which reoxidise in presence of air. Hence the volumetric estimation with titanous chloride is done in a CO₂ atmosphere. They have the following characteristic groupings: [-]


Azine Dyestitffs. - Azonium bases are derived from azines by linking an organic radicle to one of the nitrogen atoms, which is thereby changed from trivalent to pentavalent nitrogen. These bases are themselves dyestuffs, but are too feeble for commercial use without the introduction of auxochrome groups. A new branch of azines in the anthraquinone series possesses valuable vat-dyeing properties and other distinctive features which require separate treatment (see Anthracene Derivatives). The introduction of auxochrome groups into azines and azonium bases has furnished a large number of commercial dyestuffs. The first dyes of this class, safranines and indulines, were obtained by purely empirical methods. Their production by methods of oxidation involved the intermediate formation of indamines. Thus, when an ortho-amido indamine is heated in aqueous solution, it is transformed to an azine, i.e., changes from blue to red, the leuco compound formed intermediately, oxidising in the presence of air.

[-]

The simplest azine type, diphenazine, obtained by heating pyrocatechol and o-phenylene diamine, may be written [-]

Azines appear to be tautomeric bodies possessing the symmetrical type of constitution in the almost colourless free state. The ortho-quinonoid constitution (quinoxaline) is ascribed to the intensely coloured salts of azine bases, e.g., [-]

In many azine dyestuffs the presence of auxochrome groups permits of a p-quinonoid structure being assigned, as well as the ortho type shown above, e.g., Neutral Red.

These dyestuffs are, however, generally written with an ortho-quinonoid constitution [-]

Then, again, an alternative is offered, i.e., to which nucleus the quinone bonds should be attached. It is often difficult to decide among the existing possibilities in assigning quinonoid formulae to azine dyestuffs, while the symmetrical formula usually can be safely assigned, for the time being at any rate.

The azine class can be subdivided into certain well marked groups, typical members of which will suffice.

The quinoxaline class only contains one member. The parent substance is quinoxaline or phenazine.

[-]

When phenanthraquinone is condensed with o-amido diphenylamine in glacial acetic acid solution, a basic orange yellow dye is obtained, Flavinduline O, II (B.).

[-]

The mono and diamidodiphenazines are called eurhodines, e.g., Neutral Red is of the eurhodine class.

The mono and di-oxy derivatives corresponding to eurhodines are called eurhodols.

The azonium class derived from phenylphenazonium chloride includes the aposafranines and aposafranols, [-] which are respectively mono-amido derivatives of phenylphenazonium chloride and monoxy derivatives. (The auxochrome groups are meta to the pentavaleut N atom.)

The safranines are diamido-phenylphenazonium compounds. In a typical safranine both auxochrome groups are in the m-positioir to the pentavalent N atom. The corresponding di-oxy derivatives are called safranols. Bodies of the safranine type, however, having the amido groups phenylated, are called mauveines, while the introduction of other phenyl-amido groups into mauveines gives indulines.

The aposafranines derived from naphthophenazine have also been given special names according to the position of the amido group. When this is in the naphthalene ring they are called rosindulines, e.g., Induline Scarlet (B.) is a typical rosinduline.
[-]

With the amido group in the phenyl nucleus the isorosindulines are obtained, e.g., Neutral Blue (C.).
[-]

These dyes are all basic dyes and find their chief use on cotton, being applied on a tannin mordant.

Induline Scarlet also finds use as a catalyst along with formaldehyde-hydrosulphite reducing agents. By its use it is possible to discharge Naphthylamine Bordeaux in calico printing, which is unsatisfactorily performed by use of fonnaldehyde-hydrosulphites alone. Rongalite Special (B.), and certain other "special" commercial brands of these reducing agents, contain the above dyestuff as catalyst.

The Nigrosines are grey and black dyestuffs, ot which little is known as to constitution, except tkit they are related to the indulines.



Eurhodines. - This small and unimportant class may be shortly dealt with. The method of obtaining Neutral Red above described is typical. Any of the alternative methods of synthesis available for the required indamine may be employed.

Further condensation proceeds readily on heating in aqueous solution as in the case of Neutral Red.

The eurhodines are weak bases forming red monoacid salts and green di-acid salts. Only the former come into consideration for dyestuffs as the latter are dissociated in aqueous solution.

The eurhodols obtained by replacement of amido groups by oxy groups in eurhodines have no commercial importance.


Safranines. - The elucidation of the constitution of these dyestuffs presented great difficulty, and is mainly due to Hofinann, Witt, Nietzki and Bernthsen. The following facts are to be considered in adopting a formula. Indamines (blue) are well marked intermediate stages in safranine (red) formation. Safranines are obtained by heating indamines with primary monamines; also by oxidation of p-p'-diamido-diphenylamiiie in presence of primary amines, by oxidation of a p-diamine in presence of primary amines, by oxidation of a p-diamine along with a derivative of m-amidodiphenylamine, and by the commercial method of oxidising a molecule of a p-diamine with two molecules of a monamine.

By this last method it is found that the following conditions are essential to obtain a safranine: (i) the p-diamine employed must have one amido group unsubstituted, one molecule of this body being required; (ii) two molecules of the same or different monamines are required, of which one must have the p-position unsubstituted, while in the other it may or may not be substituted, but the amido group itself must be unsubstituted, i.e., a primary amine.

Witt proposed an asymmetrical formula for safranine:
[-]

The dotted cleavage lines show how well it agrees with the main facts of saf Vanine synthesis as laid down above. It has, however, been dropped and the formula proposed by Bernthsen is generally adopted: [-]

1 The asymmetric formula has recently been revived by Barbier and Sisley who stated that the commercial dye is mainly of this type. Their claim however has since been refuted by Hewitt and his collaborateurs who found their oxyaposafranone to be identical with the body obtained from p-nitrosopheuol and m-oxydiphenylamine.It was found that the number of substituted amido derivatives according to the asymmetrical formula could not be prepared. Also m-amido-o'. o'-dinitro-diphenylamine could be condensed with p-phenylene diamine to give a safranine, which is not in accordance with asymmetric substitution. Again, the same phenylsafranine is obtained in two ways: (i) by oxidation of m-amidodiphenylamine along with p-amidodiphenylamine, (ii) by oxidation of m-phenyl-amidodiphenylamine and p-phenylene diamine. These facts are not explained by the asymmetric¹ formula but quite agree with the Bernthsen formula. This latter is adapted to express either ortho or para quinone structure. Thus the simple safranine written above may be expressed: [-]

The main trend of evidence is in favour of the o-quinone formula. Safranine is strongly basic, and the base itself is not obtained in the usual way, namely, by alkali treatment of the salt. It may however be obtained by oxidation with silver oxide of the following diphenylamine derivative:
[-]

It is strongly basic, due to the peritavalent nitrogen atom which is an essential part of the ortho quinonoid structure.

The ready reoxidation of the leuco compound of safranine in air agrees also with the general behaviour of o-quinone dyestufFs in this respect. According to the p-quinone formula safranine is an imide. It is actually the case that by ordinary methods of diazotisation only one amido group can be diazotised. When this is done and the diazo body boiled with alcohol aposafranine is obtained which cannot be further diazotised by the general methods.[-]

However, by treatment in strong acid solution (green) this body can be diazotised, and also safranine can be diazotised in both amido groups, and on boiling with alcohol, plienylphenazonium chloride is obtained.
[-]

This body is reconverted into safranine base by treatment with ammonia.

Safranine base may also be obtained by treatment of the sulphate with baryta. It crystallises in green leaflets.

It may further be stated that safranine base on heating can be obtained almost free from oxygen, which is in accordance with the p-quinonoid formula.
[-]

On the other hand certain chlorine substitution products of safranol clearly support the ortho quinone structure.
[-]

The formula for aposafranol may be written from what has been explained above.

The formation of safranine by the oxidation method of synthesis is apparently due to formation of quinone derivatives, by oxidation of the p-diamine used, which then form diphenylamine derivatives by addition of molecules of amines. These diphenylamine derivatives by oxidation give indamines which have again a quinone structure and allow of further addition, giving phenylamidodiphenylamines of the type shown on page 229 from which safranine base is obtained. Further oxidation in presence of acid gives the dyestuffs found in commerce. The whole process bears considerable resemblance to the synthesis of Magenta in respect of the part played by quinone structure. (See p. 191.)

The constitutions of other dyestuffs of the azonium class have been assigned on similar evidence to that discussed above for safranine.

Commercial Safranine (many brands) is obtained by oxidation ,of equal molecules of p-tolylene diamine and o-toluidine (obtained mixed by reduction of amidoazotoluene), to give an indamine. The required extra molecule of monamine is then added, i.e., aniline or o-toluidine. The recovered oils from the Magenta melt are rich in o-toluidine, and may be used for Safranine manufacture. Potassium bichromate in hot acid solution is the oxidising agent. Mauve and other azines are also formed. Chalk is added to precipitate impurities and the dyestuff salted out of the filtrate. The salt of the dyes tuff formed with hydrochloric acid is crystalline.
[-]

Methylene Violet BN, etc. (M.) is the asymmetric ( N(CH₃) 2 ) dimethyl-phenyl safranine. Other dyes of this class are Tannin Heliotrope (C.), Rhoduline Violet (By.), Amethyst Violet (K.), etc.

Of the phenyl (C₆H₈.NH-) safranines or mauveines few are important.

Mauve itself possesses historical interest, being the first of the coal tar dyestuffs. It was obtained by Perkin in 1856 by oxidation of a crude aniline containing mixed toluidines.
[-]

It still finds some small use as a basic dye, mainly on account of its comparatively good fastness to light, which exceeds that of Methyl Violet, on that account it finds some use for blueing or " white-dyeing " of silk.

Indazine M, etc. (C.) is a blue basic dye of the mauve class, as is also Metaphenylene Blue.

Milling Blue (K.) is a sulphonated di-naphthosafranine or rosinduline of the mauve type.
[-]

Magdala Red is a basic dyestuff of the safranine class.
[-]

It is the naphthyl homologue of phenyl safranine. It exhibits fluorescence, and finds a small use on silk.

Certain rosindulines (aposafranine class) are also important, and categorically should have been dealt with before the safranines. A good deal of evidence, analogous to that brought up in discussing the constitution of safranines, has been accumulated in favour of a similar type of formula for rosindulines. The simplest rosinduline is obtainable by condensing 4amido-^-naphthoquinone with o-amido-diphenylamine, whereby two molecules of water are split off, giving the base.
[-]

The rosindulines are sometimes obtained commercially by heating simple azo compounds with α-naphthylamine hydrochloride or aryl-azo-α-naphthylamines with aniline and aniline hydrochloride (i.e., a primary amine), e.g., Induline Scarlet already mentioned is obtained from the azo compound of monoethyl-p-toluidine by melting with α-naphthylamine hydrochloride. Anilidonaphthoquinones and anilineα-naphthylamine are also used to give rosindulines by similar heating methods. The process involves the formation of intermediate bodies analogous to those found in the induline melt (see later). These have been isolated by stopping the melt before completion of the reaction. Thus, by melting benzol azo-α-naphthylamine with aniline and aniline hydrochloride, phenylrosinduline is obtained finally, by intermediate formation of a trianilido quinone:
[-]

This body can be easily prepared in good yield from β-naphthoquinone-4-sulphonic acid by heating with aniline. The first stage is reached in aqueous solution, but the second only by melting.
[-]

This trianilido quinone is a tautomeric form of the intermediate product above written. By further melting with aniline and aniline hydrochloride up to 160°C. phenylrosinduline is obtained. Thus the trianilido quinone [-] by direct condensation gives leuco-phenylrosinduline, which readily oxidises in presence of air to the dyestuff base.

[-]

The excess of aniline is dissolved out of the melt with the required amount of hydrochloric acid and phenylrosinduline filtered off. This product finds commercial use as the disulphonic acid Azocarmine G in paste (B.), which is an acid dyestuff difficultly soluble in water. The monosulphonic acid is first prepared by heating up to 95°C. with oil of vitriol. It is then purified by treatment with caustic soda and washing, and further sulphonated. This intermediate purification results in a better shade in the final product.

Phenylrosinduline hydrochloride is readily dissociated hydrolytically, and is not used as a basic dye.

Azocarmine B (B.) is the trisulphonic acid of phenylrosinduline.

By heating this dyestuff with water at 160° to 180°C. the monosulphonic acid of a rosindone is obtained.

Rosinduline 2G (K.)is the monosulphonic acid of a rosindone.
[-]

Rosinduline G (K.) is a very similar body. These are acid dyestuffs for wool.

Neutral Blue (C.) already mentioned as an isorosinduline is obtained by the action of nitroso-dimethylaniline hydrochloride on phenyl-β-naphthylamine.


Indulines. - This class includes blue, violet and blue-black dyestuffs obtained by heating amidoazobenzene with aniline and aniline hydrochloride to the boiling point, or under pressure. Almost any azo or nitroso compound on treatment in this way will give indulines. If p-phenylene diamine be added, basic indulines are obtained. The usual products are insoluble in water but soluble in alcohol, and on sulphonation give water-soluble acid dyes.

It has been found that the formation of quinone anilides plays an intermediate role in induline synthesis. Thus azophenine has been isolated and identified by stopping the melt and extracting with alcohol. It forms dark red crystals of formula [-]

The changes involved in the formation of this body from amidoazobenzene are probably of the following type:
[-]

The removal of two H atoms as required for the final stage of this process, appears to be accomplished by reduction of a certain amount of amidoazobenzene, which would account for the presence of some p-phenylenediamine found in the melt.

Quinone anilides of the azophenine type readily condense further on raising the temperature from 100° to 130°C. thus: [-]

The process of induline formation should be compared with that of rosinduline synthesis already described.

Further heating results in the introduction of more anilido groups.

The following are well known members of the induline class obtained by more or less modified processes, similar to the one described:

Indamine Blue (M.). A basic dye used instead of indigo.
[-]

Other Indamine Blue brands are obtained by heating nitroso-dimethylaniline with o- or p-toluidine.

Induline B, 3B, etc. (many brands). The spiritsoluble brands are hydrochlorides of the same type as Indamine Blue above and of the following bases:
[-]

The water-soiuble acid dyes are obtained by sulphonation of spirit-soluble indulines. Various Fast Blues, Printing Blues, Acetine Blues, etc., are of this type. Besides being acid dyestuffs suitable for wool and silk, they possess residual basic properties allowing of fixation on tannin-mordanted cotton.

Nigrosines are obtained by heating nitrobenzene with aniline and aniline hydrochloride in presence of metallic iron (filings) to 180°C. Nitrosophenol also gives dyes of this class when heated with aniline and aniline salt. They are used for pigments, shoe polishes, etc. The water-soluble acid dyes of this class are obtained by sulphonation of the blue-black or black nigrosine bases.

Aniline Black. In 1834 Runge obtained insoluble black compounds by oxidation of aniline with chromic acid. A similar precipitate was obtained by Perkin in making Mauve. It was not applied in dyeing till 1862, when Calvert obtained a fast black on cotton by oxidation of aniline in contact with the cotton fibre. Aniline black is largely produced in this way, and itself is not a commercial dyestuff.

There are three chief methods in use: (1) the socalled single-bath black is used for cotton hanks, which are treated with a cold mixed solution of aniline, potassium bichromate and sulphuric acid. Later the temperature is gradually raised. A large amount of black is precipitated in the bath and a considerable quantity of chrome is deposited on the fibre as well as aniline black itself. (2) The so-called "aged" or oxidation black is applied to cotton by padding with a solution containing aniline, aniline salt, potassium chlorate and a copper salt, the latter acting as oxygen carrier. The dried material is then "aged" in a warm moist chamber and becomes green, due to formation of emeraldine. It is given a bath of bichromate to complete the oxidation of emeraldine to aniline black. Attempts have been made to overcome the tendering of cotton in this process by replacement of the chlorate by air oxidation in presence of a trace of a catalyser, e.g., p-phenylene diamine. (3) The steam black can be reserved, and is used in calico printing. The paddingliquor contains aniline salt, potassium chlorate and ferrocyanide, and by printing on a thickened alkaline paste after drying the development of aniline black is prevented from taking place under the reserve paste in the subsequent steaming.

All these processes show similar stages in aniline black formation, namely, first a green compound called emeraldine, then a blue-black body turned green by sulphur dioxide or mineral acids. This base has been called nigraniline or greenable black. Finally, ungreenable aniline black or pernigraniline is obtained, which is not aftected by sulphur dioxide or boiling with dilute mineral acids, and is a very stable body. On reduction it gives an almost colourless leuco body which re-oxidises in air, and on oxidation a very good yield of p-benzoquinone. Complete reduction or distillation with zinc dust gives para diamines and amido-diphenylamines. The recent researches of Willstaetter and Green and their collaborateurs have increased the knowledge of aniline black. The first stage in the oxidation of aniline is the formation of phenyl quinone di-imide [-] a yellow body which polymerises in presence of acids to give emeraldine C₂₄H₂₀N₄. Further oxidation of this base gives a red compound which it is claimed by Willstaetter can polymerise to give finally aniline black. Green thinks Willstaetter's products are not those obtained in the commercial production of aniline black. The lengthy indamine formula deduced from polymerisation would not possess the stable properties of aniline black. Finally, analyses of aniline black vary, no doubt due to the black product consisting of mixtures of nigraniline with pernigraniline, some free aniline is necessary to get the fully formed black by oxidation of nigraniline, according to Green.

It has long been recognised that aniline black shows great similarity to the azines both in method of formation and properties. A considerable difficulty, however, has been experienced in the fact that the degradation products obtained from aniline black contain no ortho derivatives. The trend of evidence is in the main towards an azine structure for aniline black, to which Green has ascribed the following formula: [-]

- See Jour. Soc. Dyers, contributions by A. G. Green and others, pp. 105 and 338, 1913. Also Aniline Black, Noelting and Lehner. -

Diphenyl Black Base P (M.) consists of amidodiphenylamine and on oxidation gives an aniline black. Diphenyl Black Oil DO (M.) is a mixture of the base and aniline. The use of these bodies demands less strong oxidation on the fibre, and therefore reduces the risks of tendering the fabric.

Paramine Brown is a chocolate brown produced on the fibre from p-phenylene diarnine in a similar way to the production of aniline black. The diamine is sold for fur dyeing, etc., as Ursol D (Ber.), Furreïn D (J.), etc. Other Ursol and Furreïn dyeings are produced by por m-amidophenol. The Furrole (C.) and Nako (M.) colours belong to the same class.


Oxazine Dyestuffs. - These dyestuffs are derivatives of diphenoxazine, which is obtained by condensing o-diamidophenol with pyrocatechin.
[-]

By introducing auxochrome groups into this body leuco oxazine dyestuffs are obtained which oxidise in air to give the dyestuffs. The class exhibits great similarity to the azines in most respects. They are prepared from o-hydroxy derivatives of in dam in es or indophenols, or with these bodies as intermediate stages involved in their production. The various methods of i ml; miine synthesis may be employed to reach this stage, further condensation taking place readily on heating, by quinone change; e.g., nitrosodimethylaniline and resorcin give
[-]

This is produced on the cotton fibre by printing with a paste containing resorcin and the nitroso body with tannin as mordant. The cloth is dried and steamed; the indamine winch is first formed condenses further to give Nitroso Blue or Resorcine Blue:
[-]

It will be noted that the adoption of an o-quinonoid formula for oxazine dyestuffs demands the assumption of tetravalent oxygen.

The first commercial dyestuff of this class was Naphthol Blue D. R. New Blue R or Meldola's Blue discovered in 1879 by Meldola. It is obtained by adding gradually nitrosodimethylaniline hydrochloride to β-naphthol dissolved in its own weight of glacial acetic acid, or three times its weight of alcohol, the temperature being maintained at 110°C. under reflux condenser. The reaction is violent at first. The pure dyestuff may be separated with alcohol, but it is usually crystallised out as the double chloride with zinc. It is used for cheap indigo blue shades on tanninmordanted cotton.
[-]

By further action of excess of nitrosodimethylaniline New Blue B is obtained.
[-]

If, instead of β-naphthol, in making Meldola's Blue, 2.7-dioxynaphthalene be used, Muscarin is obtained.

Other basic dyestuffs of this class are obtained similarly thus:

Capri Blue GON (By.), nitrosodimethylaniline and dimethyl m-amidocresol.

New Methylene Blue GC (C.), dimethylamine and Meldola's Blue, and subsequent oxidation.
[-]

Nile Blue A (B.), nitrosodiethyl-m-amidophenol and α-naphthylamine.
[-]

Using benzyl-α-naphthylamine in the above condensation, one gets Nile Blue 2B (B.).

Fast Black (L.) is obtained by action of nitrosodimethylaniline on m-oxydiphenylamine.

Beside the above basic dyestuflfs some important mordant dyes belong to this group.

By acting on gallic acid in boiling methyl alcohol solution with nitrosodimcthylaniline hydrochloride, Gallocyanine (many brands) is obtained.
[-]

It gives violet blue chrome lakes, and is extensively used on wool and in calico printing. Certain brands (powder) are bisulphite compounds. On heating with aniline, followed by sulphonation, it gives Delphin Blue B (By.), an acid mordant dyestuff, the -COOH group being replaced by -NH-C₆H₄-SO₃ NH₄.

Modern Blue, Modern Cyanine, Indalizarin, Prune, etc., are Gallocyanine derivatives.

Prune pure (S.) is obtained by using, instead of gallic acid (-COOH), the methyl ether (-COOCH₃).

Gallamine Blue paste (By., G.) is obtained by using gallamide (-CO NH₂) instead of gallic acid (COOH).

Gallanil Violet (D.H.) is obtained by use of the anilide of gallic acid (-CO.NH.C₆H₅).

Corein is the diethyl analogue of Gallamine Blue.

There are many others of this class.

The oxy-derivatives of the oxazine class corresponding to safranones are of no commercial value.


Thiazine Dyestuffs. - These are closely allied to the azine and oxazine groups. They contain one atom of sulphur, which is regarded as tetravalent in the o-quinonoid formula. Lauth's violet was the earliest known colouring matter of this class. It was obtained in 1876 by oxidation of p-phenylene diamine with ferric chloride in acid solution in presence of sulphuretted hydrogen. The violet thus obtained has no commercial value, but substitution of dimethyl-p-phenylene diamine for the simple diamine by Caro gave Methylene Blue. The constitution of the thiazines has been largely built up from the work of Bernthsen on these two dyestufls. He nitrated thiodiphenylamine, obtained by heating diphenylamine with sulphur, and on reduction obtained the leuco base of Lauth's violet which oxidised in presence of air to give the dyestuff.
[-]

Hence also the constitution of Methylene Blue: [-]

Bernthsen devised a new and cheaper synthesis of this dyestuff. Nitrosodimethylaniline i reduced with iron filings, and the resulting solution of dimethyl-pphenylene diaiume is oxidised in dilute acid solution with bichromate, in presence of sodium thiosulphate. A thiosulphonic acid is formed: [-]

This body can be obtained as white crystals, but is never isolated from solution in the manufacture of Methylene Blue. An extra molecule of dimethylaniline is added, and with further oxidation gives an indamine thiosulphonic acid.

This greenish blue body on boiling with zinc chloride solution gives the dyestuff, by first losing ELSO 4 , and the leuco-azine thus formed oxidises rapidly in air, or in presence of the acid oxidising agent. The dyestuff is put out commercially as a double chloride with ZnCl₂.
[-]

Methylene Blue is largely used on tannin-mordanted cotton and as a basic "topping" colour, i.e., for brightening up other shades. It is faster to light than most basic dyes. It .is used as a stain in microscopy, and as free base finds internal use as a medicine.

New Methylene Blue N, GB, R, etc. (C.) is obtained when mono-ethyl-o-toluidine is used as in the synthesis last described.
[-]

Certain brands of this name are oxazines, see p. 243.

Methylene Green (many brands) is obtained by nitration of Methylene Blue with sodium nitrite and hydrochloric acid.
[-]

It is not known for certain to which nucleus the o-quinonoid bonds should be attached.

Thionine Blue O, B, etc. (M., By.) is the trimethylethyl product analogous to Methylene Blue (a tetramethyl product) and is similarly prepared.

The above are all basic dyestuffs. The only acid dyestuff of outstanding interest belonging to this class is Thiocarmine R (C.). This dyestuff is made by a thiosulphonic acid process, similar to that described for Methylene Blue, using p-amidoethylbenzylaniline sulphonic acid as starting point.
[-]

The thiosulphonic acid of this body is oxidised to form an indainine with ethylbenzylaniline sulphonic acid, which gives finally a blue acid dye:
[-]

There are several important acid-mordant dyes of the thiazine class.

Indochromogen S (S.) is obtained by condensation in dilute alkaline solution of p-amidodiethylaniline thiosulphonic acid with 1.2-naphthoquiiione-4.6-disulphouic acid.
[-]

It gives blue shades on a chrome mordant.

Brilliant Alizarin Blue G, R, etc. (By.) is obtained by a similar method and is the dimethyl body corresponding to Indochromogen S (diethyl). Sulphobenzyl ethyl-p-phenylene diamine and analogous compounds give similar dyestuffs.


- Additional information may be obtained from sections of Thorpe's Dictionary of Applied Chemistry, where may also be found patent references, etc.  -