The Chemistry of Dyestuff. Intermediate Compounds. IV. Amido Compounds.

A Manual for Students of Chemistry and Dyeing
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)
Amidation. By amidation is meant the preparation of amido compounds by the introduction of the NH2 group. The most important method for the production of amido compounds is by reduction of nitro compounds. As reducing agents, iron in presence of hydrochloric or acetic acid is the most important, and to a smaller extent zinc, tin, sodium sulphide, sulphurous acid and its salts, sodium hydrosulphite, caustic soda and glucose, etc. Of great importance is the nature of the reduction, whether it be in acid, neutral, or alkaline solution. For example, nitrobenzene gives on reduction in acid solution aniline C6H5NH2 , in neutral solution phenylhydroxylamine C6H5NHOH, and in alkaline solution hydrazobenzene C6H6.NH.NHC6H5.

Aniline [-] (M.P.8deg;C., B.P. 182°C.) is manufactured  in iron vessels by reducing nitrobenzene with scrap iron and a small amount of hydrochloric acid. A large horizontal boiler is fitted with a propeller or shovel stirring gear and also a hollow axle constructed for steam distillation. Iron filings, nitrobenzene, water, and about 3 per cent, of hydrochloric acid on the weight of nitrobenzene are introduced into the vessel. The contents are well stirred, and steam passed into the vessel. Water, nitrobenzene, and aniline distil; the distillate is condensed and the oil returned to the reduction vessel until the nitrobenzene is completely reduced. This is observed from the colour, smell, and specific gravity of the oily distillate. The condensed and separated water, containing 3 per cent, of aniline, is run back to the steam boiler. The aniline may be rectified or again steam distilled to further purify it. When pure it is a colourless, highly refractive liquid. The commercial aniline may contain about 2 per cent. of nitrobenzene, and on keeping changes colour to yellow or red, this change being probably due to a trace of amido-thiophene. Aniline for the production of aniline black should be tested for the toluidines and nitrobenzene, or reddish azine dyes will be formed along with the black.

The so-called "aniline for red" is a mixture of aniline with orthoand para-toluidines, obtained from the mixed nitrotoluenes, and it is employed for the manufacture of Magenta.

The reactions that take place when nitrobenzene is reduced with iron may be represented as follows:

I. Fe + 2HCl ? FECl2 + 2H.

II. 6FeCl2 + C6H5NO2 + 4H2O = 4FeCl3 + C6H5NO2 + Fe2(OH)6.

III. 2FeCl2 + Fe = 3FeCl2

From these equations it is obvious why iron in presence of a small amount of acid is capable of reducing a large amount of nitro compound.

The full equation may therefore be expressed:
C6 H5NO2 + 2Fe + 4H2O = C6H5NH2 + Fe2(OH)6 .

Aniline, being a basic compound, is capable of producing salts; one of the most important is "Aniline Salt" or aniline hydrochloride C6H5NH2.HC1. It is obtained by mixing aniline with concentrated hydrochloric acid in molecular proportions and then allowing the aniline salt to crystallise out. Aniline sulphate is prepared similarly.

Other amines prepared in a similar manner to aniline are orthoand para-tojuidine, the xylidines, and a-naphthylamine. In some cases the nitrotoluenes are not separated, but are converted into toluidines by direct reduction of the crude nitrotoluene; the crude product consists of about 32 to 38 per cent, of para-, 60 to 65 per cent, ortho-, and about 2 per cent, of meta-toluidines. By strongly cooling, the para-isomer crystallises out, and may be filtered, or, better, the mixture is treated with sodium phosphate (Na2HPO4) solution, with which the para-toluidine forms an insoluble compound; but probably the cheapest method is that of churning and cooling with water or with ice. The para-toluidine forms a crystalline hydrate which may be easily removed and purified. Para-toluidine may be detected in the presence of aniline and o-toluidine by addition of ferric chloride to a hydrochloric acid solution of the mixture. With the para compound a Bordeaux red solution is obtained. If o-toluidine and aniline are present a greenish blue precipitate is formed, which on filtration gives a red filtrate.

The xylidines are usually prepared mixed from unseparated nitroxylenes; the meta-xylidine is the most important.

In the case of naphthylamine ordinary steam distillation is not sufficient to separate it from the sludge. Superheated steam may, however, be used; or, preferably, extraction with solvent naphtha is employed. All these amines are in use for the manufacture of azo / dyes, besides the similar use of a large number of their

Derivatives of Aniline. There are two classes of derivatives, those in which the substitution takes place in the ring and the amido substitution derivatives. Of the latter class, the most important are mono-methylaniline, dimethyland diethyl-aniline, diphenylamine, and benzylaniline.

The ring-substituted derivatives of aniline are very important, of which the following may be taken as typical examples: ortho-, meta-, and para-nitranilines, chloroanilines.

The introduction of the nitro group into aniline gives compounds solid at the ordinary temperature. These compounds are far less basic than aniline so that their salts are hydrolysed by water with separation of the free base. Aniline hydrochloride on the other hand is stable even in very dilute aqueous solution.

On account of the oxidising action of nitric acid upon aniline it is impossible to nitrate directly. The amino group is therefore shielded by acetylation.

Acetanilide [-] is obtained by boiling aniline and glacial acetic acid in an enamelled iron vessel, fitted with a reflux condenser, until the boiling point of the mixture reaches 250° to 270°C. The product is run into trays where it sets on cooling. It is ground to powder in a mill and nitrated directly. The nitration is carried out in an iron vessel similarly to the manufacture of nitrobenzene. The finely powdered acetanilide is well mixed with some concentrated sulphuric acid; into this mixture the theoretical amount of nitrating acid (calculated upon the nitric acid) is gradually added. The contents of the vessel are thoroughly agitated and the temperature kept between 10 and 15°C. The reaction product is run into cold water in a lead lined vessel and thoroughly mixed with a revolving paddle agitator. The precipitated paranitracetanilide [-] is filter-pressed, washed with water and hydrolysed. There is also obtained about 4 per cent, of ortho-nitracetanilide; this may be removed by chloroform or water.

The para-nitracetanilide is hydrolysed by boiling with 25 per cent, sulphuric acid. The para-nitraniline  [-]  is precipitated in a finely divided state by running into cold water with agitation, filtered, and dried. It is applied for the production of Para Red and in the manufacture of azo dyes. It is a yellow compound, nonvolatile with steam, and melts at 147°C.

Pure para-nitraniline is most readily obtained by nitrating benzilidene aniline  [-], the nitro derivative being then hydrolysed with dilute caustic potash.

Nitracetanilide on reduction gives para-amidoacetanilide, which is largely used for the production of azo dyes.

In order to obtain a larger yield of o-nitraniline (M.P. 71,5°C.), acetanilide is treated with sulphuric acid at 50°C., followed by addition of nitrating acid, keeping the temperature at 40° to 50°C. The product is precipitated with water, deacetylated by steam, cooled to 50°C., and poured on ice. The o-nitraniline is precipitated, the para compound remaining in solution. A yield of 25 per cent, of the ortho compound may be obtained.

Meta-nitraniline  [-] (M.P. 110°C.). This is  obtained by reduction of one nitro group of m-di nitrobenzene. Such partial reduction is effected by prolonged action of cold sodium sulphide solution. A similar method is used for reducing nitro groups in azo dyes without the azo group also suffering reduction.

Aniline Sulphonic Acids. There are three isomerides of which the para compound, usually called sulphanilic acid, is the most important, and secondly the meta or metanilic acid. These acids are used commercially in large quantities for the manufacture of azo dyes, etc.; the ortho acid does not yet find application commercially.

The para-aniline sulphonic or sulphanilic acid  [-]  is manufactured by the "baking process." Molecular quantities of aniline and sulphuric acid are mixed together with stirring, aniline sulphate is formed; this solid substance is heated in shallow layers upon trays at 180 to 220°C. until the product is completely soluble in dilute caustic soda. The product is dissolved in water, filtered from carbon, and allowed to crystallise.

Metanilic acid  [-] is obtained by sulphonating nitrobenzene with fuming sulphuric acid, running the product into water and reducing by means of iron filings.

Aniline Garboxylic Acids. By the nitration of benzoic acid a mixture of three isomers is obtained consisting of about 80 per cent, meta-nitrobenzoic, 15 per cent, para-nitrobenzoic and 5 per cent, of orthonitrobenzoic acid.

Ortho-nitrobenzoic or Anthranilic acid  [-] (M.P. 145°C.) is much employed in the dyestuff industry. It is obtained in several stages from naphthalene, the first being oxidation with  [-]  sulphuric acid in presence of mercury sulphate; at 250° to 270°C. sulphur dioxide, carbon dioxide, and water are given off, at 300°C. phthalic and its anhydride distil. The mercury sulphate remains behind and is used for the next charge. Phthalic acid  [-] (M.P. 213°C.) readily loses water on heating forming phthalic anhydride (M.P. 128°C., B.P. 284°C.). It is used for the manufacture of Fluorescein, Rhodamine, etc.   [-]

Phthalimide (M. P. 238°C.) is obtained by heating phthalic anhydride and ammonium carbonate at 225°C. until the mass, which at first liquefies, again solidifies. After cooling it is dissolved in water and recrystallised.


The phthalimide is dissolved in cold caustic soda solution and treated with the theoretical quantity of sodium hypochlorite (Hoffmann's Reaction), the solution is then quickly heated to 80°C. at which temperature the reaction rapidly takes place. The solution is neutralised with sulphuric acid and the anthranilic acid precipitated by addition of acetic acid. It is used in the synthesis of indigo and for preparing thiosalicylic acid, which is used in the synthesis of certain indigoid vat dyes.


N -substituted aniline derivatives. The alkyl and aryl derivatives of aniline are extensively used in the manufacture of the basic dyestutls.

Monomethylaniline  [-]  is obtained by  heating aniline, aniline hydrochloride and methyl alcohol (free from acetone) under pressure in an autoclave to 200°C. The bases are separated by milk of lime followed by steam distillation. The oil separated from the distillate is a mixture of aniline, and monoand (liinethylaniline. This oil is acetylated, as in the preparation of acetanilide, and then distilled. The dimethylaniline distils off, the residue is hydrolysed by boiling with dilute sulphuric acid, then made alkaline with milk of lime, and distilled. Monomethylaniline is a colourless oil (B. p. 191°C.).

Monoethylaniline  [-] is obtained similarly (B.P. 204°C.).

Benzylaniline  [-] is obtained in the  same way except that benzyl chloride is substituted for the alcohol, arid the reaction temperature is lower, viz., 160° to 170°C.; M.P. 31° to 33°C.

Dimethylaniline C6H5N(CH3)2 (B.P. 192°C.). This compound is manufactured by heating aniline, aniline hydrochloride, and methyl alcohol in an autoclave at 200° to 230°C. during ten hours (Fig. V, Appendix). The reaction product is made alkaline with milk of lime and the bases separated by steam distillation. The oil may then be rectified by distillation* As impurity there is generally a little monomethylaniline. Dimethylaniline is a colourless oil, and is largely used in the colour industry.

Diethylaniline C6H5N(C2H5)2 (B.P. 213°C.) is obtained similarly, it is a colourless oil.

Diphenylamine C6H5NHC6H5 (M.P. 54°C., B.P. 310°C.) is obtained by heating aniline and aniline hydrochloride in an autoclave at 220°C. (Fig. III, Appendix). The reaction product is dissolved in boiling concentrated hydrochloric acid, poured into a large quantity of water, and the base, which separates out, is redistilled. A blue colour is obtained with traces of nitrates, nitrites or chlorates in strong sulphuric acid.

Naphthylamines. α-naphthylamine  [-]  (M.P. 50°C., B.P. 300°C.), see p. 29.

β-naphthylamine [-] a (M.P. 112°C., B.P. 294°C.). Since by the nitration of naphthalene only the alpha position is substituted, the ß-naphthylamine must be obtained from naphthalene ß-sulphonic acid or from ß-naphthol. One molecule each of ß-naphthol and of ammonium sulphite, and one and three-quarter molecules of ammonia (25 per cent, solution) are heated in an autoclave at 150°C. during about ten hours. The crude product is treated with caustic soda to remove unaltered ß-naphthol, then dissolved in hydrochloric acid, filtered from the insoluble ß-dinaphthylamine, and separated from the hydrochloric acid solution by milk of lime or soda. When pure it is colourless and almost odourless.

The addition of ammonium sulphite greatly reduces the temperature at which the reaction takes place. The reaction is probably as follows: a sulphurous acid ester is first obtained:
the ester is then decomposed with reformation of ammonium sulphite:

If the ammonia is replaced by primary or secondary amines, secondary or tertiary amines are obtained.
Alkylnaphthylamines are obtained similarly to the alkylanilines.

The phenylnaphthylamines, α and β, are prepared from the corresponding naphthols by heating with aniline and aniline hydrochloride.

Diamines. The diamines that are important in the dyestuff industry are metaand para-phenylene diamines and the corresponding tolulene diamines, benzidine, its homologues and derivatives, 1.5 and 1.8-naphthylene diamines, and para-amido-diphenylamine.

Meta-phenylene diamine [-](M.P. 83°C., B.P. 287°C.) is obtained by the reduction of m-dinitrobenzene under similar conditions to the preparation of aniline. It gradually turns brown when exposed to the air, and is soluble in acid, water, or alkaline carbonate solutions. It is employed as a developing agent and for the production of dyestuffs.

Para-phenylene diamine [-] (M.P. 147°C., B.P. 267°C.) is obtained by the reduction of amino-azobenzol hydrochloride in dilute alcoholic solution or aqueous suspension by means of zinc dust, the temperature being maintained between 60°C. and 70°C. After reduction the solution is made alkaline with soda and the aniline removed by steam distillation. The liquor remaining is concentrated till the para-phenylene diamine crystallises out.

This method for the production of para-diamines is of general application. P-phenylene diamine is used in the manufacture of sulphide dyes, and for the production of browns on fibres by means of oxidising agents.

Naphthalene diamines. Of the many possible isomers only the 1.5 and the 1.8-diamido naphthalenes are important. They are obtained from the corresponding dinitronaphthalenes by reduction with sodium or ammonium sulphide.

1.5 -Naphthalene diamine [-] crystallises in needles (M.P. 189,5°C.), it sublimes without decomposition, forms a hydrochloride [-] and a sulphate [-]. Nitrous acid converts it into a tetrazo compound. It is used for the production of azo dyes, many of these dyes having direct affinity for cotton.

1.8-Naphthalene diamine [-] crystallises in  needles (M.P. 67°C.) and forms salts similar to the 1 . 5derivative. By treatment with nitrous acid a red azimide is formed [-]. Azo dyes are produced from it by coupling with diazotised Primuline, etc.

Many of the naphthalene diamine sulphonic acids are employed for the production of dyestuffs. These are obtained as follows:
(a) By reduction of azo derivatives of naphthylamine sulphonic acids.
(b) By heating the naphthol disulphonic acids with ammonia under pressure.
(c) Nitration and reduction of amino sulphonic acids.
(d) Action of sodium bisulphite upon naphthoquinone derivatives, etc.

Benzidine [-] (M.P. 122°C.) is the  mother substance of most direct cotton dyes and is obtained from nitrobenzene. Nitrobenzene is treated with zinc dust in alcoholic solution heated in a vessel provided with a reflux condenser, caustic soda is added to the solution, and the heating continued until the zinc has practically disappeared. The alcohol is distilled and the residue treated with hydrochloric acid, added in small quantities at a time, until an acid solution is obtained; the temperature must not exceed 35°C.; finally the solution is boiled, filtered hot, and the benzidine precipitated as sulphate by addition of sulphuric acid or sodium sulphate. Benzidine sulphate is only sparingly soluble in water. It is extensively used in the preparation of direct cotton dyes.

Tolidine [-] (M.P. 129°C.) is obtained  by a similar method from o-nitrotoluene, and Dianisidine [-] (M.P. 168 to 172°C.) from o-nitroanisol. Diphenetidine is the corresponding compound obtained from o-nitrophenetol [-]

By the nitration of diacetylbenzidine either monoor dinitro-benzidine may be obtained. The diacetylbenzidine is dissolved in sulphuric acid with nitric acid added in quantity sufficient to form either the mono- or dinitrocompound. The product is precipitated by addition of water and the acetyl derivative hydrolysed by boiling with dilute hydrochloric acid, or strong caustic soda.

Dinitrobenzidine [-] is a red compound (M.P. 218° to 221°C.).

Mono-nitrobenzidine[-](M.P. 143°C.) is a red compound obtained from benzidine, generally by the addition of the theoretical quantity of potassium nitrate to a sulphuric acid solution of benzidine. The nitro group being in the meta position to the amido group.

Dichlorobenzidine[-] (M.P. 133°C) is prepared by the direct chlorination of diacetylbenzidine and hydrolysis of the product with boiling hydrochloric acid.

Benzidinesulphone [-] is obtained by heating benzidine sulphate with excess of fuming sulphuric acid (20 per cent. SO3), the product is poured on to ice, filtered and separated from the accompanying benzidinesulphone monoand di-sulphonic acids by means of caustic soda. Benzidinesulphone melts above 350°C.

Benzidine dicarboxylic acid (Diamidodiphenic acid). [-] Prepared by reduction of ortho-nitrobenzoic acid with zinc dust and caustic soda, followed by transformation of the hydrazobenzene derivative by boiling with dilute hydrochloric acid.

Ei kommentteja :