The Natural Organic Colouring Matters
By
Arthur George Perkin, F.R.S., F.R.S.E., F.I.C., professor of colour chemistry and dyeing in the University of Leeds
and
Arthur Ernest Everest, D.Sc., Ph.D., F.I.C., of the Wilton Research Laboratories; Late head of the Department of Coal-tar Colour Chemistry; Technical College, Huddersfield
Longmans, Green and Co.
39 Paternoster Row, London
Fourth Avenue & 30th Street, New York
Bombay, Calcutta, and Madras
1918
Kaikki kuvat (kemialliset kaavat) puuttuvat // None of the illustrations (of chemical formulas) included.
The catechol tannins are characterised among other distinctive features by the important fact that when digested with boiling dilute mineral acids a red precipitate, known as "anhydride" or "phlobaphene," is produced. The designation "catechol" arises from the fact that the majority of these substances give a green coloration with ferric chloride, and protocatechuic acid or catechol as one of their decomposition products. Such a classification is, however, misleading, in that by comparison with gallotannin, one is led to infer that these substances are similarly constituted and derived from diprotocatechuic acid only (OH)2C6H3.CO.O.C6H3(OH)COOH
When hydrolysed, however, diprotocatechuic acid gives two molecules of protocatechuic acid without production of phlobaphene (Emil Fischer, private communication). Moreover, certain phlobaphene- yielding compounds are now known to exist in which a catechol nucleus is absent. Thus the cyanomaclurin of Jakwood (q.v.) is an instance in point, for although it contains only phloroglucinol and resorcinol nuclei, it readily yields a red anhydride of this character (cf. also Mimosa tannin, Pistachia tannin, and Maletto tannin). Evidently therefore the phlobaphene reaction is either due to the special structure of the tannin itself, or to the presence of a second phenolic grouping other than catechol in the molecule. This structure may perhaps vary in certain cases, but until this is clear it appears to be preferable to include all phlobatannins under one group rather than to complicate the subject by the introduction of subdivisions.
Bottinger and Etti (loc. cit.} have suggested a benzophenone structure for certain tannins, and this applied to the phlobatannins has, at first sight, the merit that maclurin (see Old Fustic) with dilute hydrochloric acid gives rufimoric acid (Wagner, Jahres., 1851, 420), a red amorphous phlobaphene-like mass. Kinoin (see Kino), usually regarded as the methyl ether of a pentahydroxybenzophenone, is readily transformed into kino-red, whereas aromadendrin (see Kino), apparently also a benzophenone derivative, resembles, according to Maiden and Smith, catechin in many of its properties. It has not yet been ascertained if the carboxylic acids of certain hydroxybenzophenones are tannins, but on the other hand it is to be remembered that compounds possessing such a structure will be strong mordant dye-stuffs, a property which is generally absent from tannins of the so-called catechol type. As already indicated, many phlobatannins are known which contain two distinct nuclei, more frequently phloroglucinol in addition to catechol, a fact which in these cases accounts for their reactivity with diazobenzene. More difficult to understand, however, is the precipitation of all phlobatannins in aqueous solution with bromine; this could be accounted for in those instances in which phloroglucinol or resorcinol nuclei are present in the compound, but curiously enough no difference in this respect appears to have been observed in cases where evidence as to the existence of these latter groupings has been of a negative character. Though by incautious alkali fusion, the existing phloroglucinol nucleus may escape detection and probably in many instances has done so, this evidence is such that it is hard to presume that in all cases bromine precipitation arises from the presence in these compounds of a specific phenolic grouping.
It is most probable that the phlobaphene reaction is, in many cases, to be assigned to the well-known reactivity of the phloroglucinol group present in these substances, and this has also been suggested by Emil Fischer. Thus coloured compounds can be obtained by the interaction of phloroglucinol with many aldehydes, of which the red phloroglucinol vanillein is an example, and moreover the phloroglucides of Counder (Ber., 1895, 28, 26), prepared by passing hydrogen chloride into mixtures of phloroglucinol and various sugars in aqueous solution, are coloured, the d-galactose phloroglucide possessing a red tint. Again, by boiling dextrose and phloroglucinol with dilute hydrochloric acid, a brownish-red precipitate of a phlobaphene-like character can be easily produced (private communication). Interesting in this respect also is the "phlorotanninred" of Schiff (Annalen, 245, 40), which he obtained by heating his so-called diphloroglucinol carboxylic acid to 160-175°.
That phlobatannins like gallotannin owe their tanning property, as a rule, to the depside grouping appears likely, and it has indeed been observed by Trimble ("The Tannins," ii., 91) that tannins from various species of oak, on long digestion with boiling 2 per cent. hydrochloric acid, give not only phlobaphene but some quantity of protocatechuic acid.
In the light of the researches of E. Fischer and Freudenberg (loc. cit.), it is also to be anticipated that many of these compounds will be eventually found to possess a sugar nucleus.
Closely connected with the phlobatannin group are the welldefined crystalline substances catechin, aca-catechin and cyanomaclurin, to the first of which the constitution has been assigned by v. Kostanecki and Lampe.
Catechin, although not a tannin, reacts with pine wood and hydrochloric acid, gives with bromine water the insoluble bromcatechuretin and readily yields substances of a phlobaphene character. Though the evidence is not precise it is stated by Loewe and also by Etti that catechin can be readily transformed into catechutannic acid, a substance existing side by side with it in the plant and possessing properties typical of the phlobatannin group. It has indeed been surmised that the catechol tannins of certain plants may owe their origin to the prior existence of substances of the catechin type, and that in addition to the compounds previously enumerated, the so-called quebracho resin and guarana catechin are intermediate products of tannin formation. Again, according to Procter (private communication), a colourless catechin-like substance is to be found in mangrove cutch.
With the exception of coca-tannic acid, no crystalline catechol tannins have been described, but all are amorphous and very similar in appearance to natural gallotannin, although on keeping, especially in the moist condition, they are apt to develop a red tint. According to Perkin, most phlobatannins can be prepared in a nearly colourless condition by extracting a solution of the crude tannin to which sodium bicarbonate has been added with ethyl acetate (cf. Gallotannin).
Numerous phlobatannins have been isolated, and a description of them is given below, although it is extremely doubtful whether the majority of these are individuals. In many cases, indeed, the general reactions of these compounds are the same, and considering the extreme difficulty in the effective purification of amorphous preparations of this character, specific differences which have been observed will no doubt, on further investigation, largely disappear. Trimble (loc. cit., ii., 132), who submitted certain phlobatannins to careful purification, found that there was a fair approximation in their percentage compositions, and it is thus natural to presume that the known members of this group are not so numerous as was formerly considered to be the case.
Anachueta wood and bark contain a tannin which gives a green coloration with iron salts.
Aspertannic acid, C14H16O8, was obtained by Schwarz from Woodruff (Asperula odorata, Linn.), and gives a green colour with ferric salts. It does not yield precipitates with albumen, gelatin, and tartar emetic solutions.
Atherospermatannin, from the bark of Atherosperma moschatum (Labill.), gives a green colour with ferric salts. A lead salt, C10H14PbO3, has been described by Zeyer (Jahrb. Min., 1861, 769).
Barbitamao tannic acid, from the bark of the Stryphnodendron barbatimum (Mart), (Wilbuszwitcz, Ber. Ref., 1886, 19, 349), is an amorphous red powder, which yields a phlobaphene, and on fusion with alkali, protocatechuic acid and phloroglucinol.
Beech tannin, from the bark of the red beech, contains a tannin of the composition C20H22O9 (Etti, Monatsh., 10, 650).
Caffetannic acid, C15H18O9, occurs in coffee berries in the form of calcium and magnesium salts (Rochleder, Annalen, 59, 300); in cainia root, Chiococca brachiata (Ruiz, et Pav.), (Rochleder and Hlasiwetz, ibid., 1848, 66, 35); Nux vomica (Sander, Arch. Pharm., 1897, 235, 133); St. Ignatius beans (ibid.}, and Paraguay tea, Ilex paraguensis (A. St. Hill.), (Rochleder, Annalen, 1847, 66, 39), (cf. also Graham, Stenhouse and Campbell, J. pr. Chem., 1856, 69, 815; Arata, Ber., 1881, 14, 2251; Kunz-Krause, Arch. Pharm., 1893, 231, 613; Ber., 1897, 30, 1617).
It is an amorphous powder readily soluble in water, gives a darkgreen coloration with ferric chloride, and when boiled with potassium hydroxide solution gives caffeic acid and a sugar (Hlasiwetz, Annalen, 1866, 142, 220), which is glucose (Sander, loc. cit.). On dry distillation catechol is formed, and by fusion with alkali protocatechuic acid is obtained. The ammoniacal solution becomes green on exposure to air with formation of viridic acid, a substance which is also present in coffee berries in the form of its calcium salt (Rochleder, Annalen, 63, 197). According to Griebel (Inaugural Diss. Munich, 1903) caffetannic acid is C18H24O10, and a penta-acetyl derivative corresponding to this formula is described.
Callutannic acid, C14H14O9, contained in heather, Calluna vulgaris (Salisb.), is an amber-coloured substance. It gives a green coloration with ferric chloride, and when heated with dilute mineral acids yields an amorphous anhydro derivative, C14H10O7 (Rochleder, Annalen, 84, 354; Sitz. Ber., 9, 286).
Canaigre tannin is present in the tuberous roots of the Rumex hymenosepalus (Torr.), an important American tanning material. It has been submitted to an elaborate examination by Trimble ("The Tannins," 1894, ii., 115), who describes it as a yellowish-white powder readily soluble in water, which gives with lead acetate solution a yellow precipitate, and with ferric chloride a green precipitate. It reacts with bromine water to give a yellow deposit, and on heating to 160-190° is decomposed with production of catechol. Boiling 2 per cent, hydrochloric acid yields an insoluble red phlobaphene together with some protocatechuic acid. Sugar is not formed in this decomposition. Analysis gave C = 58,10; H = 5,33, figures which approximate to, though they are somewhat lower than, those given by the best-known phlobatannins.
Catechutannic acid (see Catechu).
Cherry bark tannin, C21H20O10+½H2O, is present in the bark of the Prunus cerasus (Linn.), (Rochleder, Sitz. Ber., 59, 819), and gives a green coloration with ferric chloride. It is not a glucoside, but when digested with boiling dilute acids gives a red phlobaphene, C21H16O8+¾H20.
Cocatannic acid, C17H22O10+2H2O (?), present in the leaves of the Erythroxylon coca (Linn.), (Niemann, Jahrb. Min., 1860, 386), is sparingly soluble in cold water and gives a green coloration with ferric salts. According to Warden (Pharm. J., 18, 985) it can be obtained in microscopic crystals of a sulphur yellow colour.
Colatannin or Kolatannin, C16H20O8, a light red amorphous powder, exists in the Kola nut, Cola acuminata (Schott and Endl.), in combination probably with caffeine and theobromine (Knox and Prescott, Amer. Chem. J., 1897, 19, 63). With ferric acetate it gives a green coloration, and on fusion with alkali protocatechuic acid is obtained. Penta-acetylkolatannin, C16H15O8(C2H3O)5, colourless powder, tribromkolatannin, C16H17O8Br3, red-brown powder, penta-acetyl-tribromkolatannin, C16H12O8Br3(C2H3O)5, pentabrom, and hexabromkolatannin have been described. On heating, kolatannin yields various anhydrides, (C16H19O7)2O at 107-110°, (C16H17O6)2O at 135-140°, and C16H16O6 at 155-156°.
Cortepinitannic acid, C32H24O17, occurs together with pinicortannic acid in the bark of the Scotch fir, Pinus sylvestris (Linn.), It consists of a bright red powder, the aqueous solution of which gives an intense green coloration with ferric chloride (Kawalier, Sitz. Ber., 11, 363).
Euphrasia tannin is present according to Enz (Vierteljahrsch. Pharm. J., 8, 175) in the green parts of Euphrasia officinalis (Linn.), and gives a green colour reaction with ferric salts. Its lead salt has the composition C32H20Pb3O20.
Fragarianin, v. Strawberry tannin.
Filitannic acid, C41H36NO18 (?), exists in fern-root (Aspidium filix mas, Swartz.), (Malin, Annalen, 143, 276), and forms a red-brown powder which, in aqueous solution, gives an olive-green coloration with ferric chloride. By boiling with dilute sulphuric acid it gives filix red, C20H18O12, an amorphous compound, and this when fused with alkali gives phloroglucinol and protocatechuic acid (cf. also Reich, Arch. Pharm., 1900, 238, 648).
Fraxitannic acid, C26H32OH (?) occurs in the leaves of the as tree, Fraxinus excelsior (Linn.). It consists of a brownish-yellow deliquescent powder, and when heated at 100° loses water and forms an almost insoluble anhydride, C26H30O13 (Gintl and Reinitzer, Monatsh., 3, 745). Aqueous ferric chloride produces a dark green coloration, and when oxidised with permanganate this tannin yields quinone. Acetylfraxitannic acid, C26H28O14(C2H3O)4, benzoylfraxitannic acid, C26H28O14(C7H5O)4, tribromfraxitannic acid, c26H29Br3O14, and tetra-acetyltribromfraxitannic acid, C26H25Br3O14(C2H3O)4, have been described.
Galitannic acid, C14H16O10, H2O, exists in the bark of the Galium verum (Linn.), (Schwarz, Annalen, 83, 57). It gives a yellow precipitate with basic lead acetate and a green colour reaction with ferric chloride.
Guarana tannin is present in the Paullinia cupana (H. B. and K.), the seeds of which, known as "guarana," contain theine and are extensively used in South America for medicinal purposes. According to Nierenstein (Die Gerbstoffe, 20) the tannin consists of small colourless crystals, melting-point 199-201°, and yields an acetyl derivative, melting-point 134-136°. It is laevo-rotatory, having [a]D20=72,4° in water, and [[a]D20=-39,1° in alcohol.
Hemlock tannin, C20H18O10 (?) is present in Hemlock bark, Tsuga [Abies] canadensis (Carr.), the extract of which is prepared on a very large scale in North America for tanning purposes. According to Bottinger (Ber., 1884, 17, 1125), it is probably related to the quercitannic acid of the oak, and on heating with sulphuric or hydrochloric acid gives the anhydride hemlock red, C40H30O17. With hydrochloric acid at 180, hemlock red evolves methyl chloride; when heated with acetic anhydride the acetyl compound is produced, whereas bromine gives a mixture of the compounds C40H20Br10O11 and C40H16Br14Oi7. Bromine added to the diluted tannin extract precipitates tetrabromhemlock tannin, C20H14Br4O10, a yellow powder which yields the penta-acetyl derivative C20H9Br4O10(C2H30)6, and by the further action of bromine the bromine compound C20H12Br6O10 (cf. Trimble, Amer. J. Pharm., 1897, 69, 354, 406; J, Soc. Chem. >Ind., 1898, 17, 558) is produced.
Hop tannin, C22H26O9, present in hops (Humulus lupulus, Linn.), (Etti, Annalen, 180, 223; Monatsh., 10, 651), has all the properties of a catechol tannin. It gives with ferric chloride a dark green coloration and with boiling dilute mineral acid the phlobaphene "hop red," C38H26O15. Hop red forms a cinnamon-coloured powder and on fusion with potash yields phloroglucinol and protocatechuic acid.
Horse chestnut tannin, C26H24O12, is present in nearly all parts of the Aesculus hippocastanum (Linn.) and in the root bark of the apple tree (Rochleder, Sitz. Ber., 53, [ii.], 478; 54, [ii.j, 609). It consists of a nearly colourless powder, the solution of which gives a green coloration with ferric chloride, and when boiled with dilute mineral acid the phlobaphene C26H22O11 or C26H20O10. On fusion with alkali, phloroglucinol and protocatechuic acid are produced. V. also phyllascitannin and CHESTNUT EXTRACT.
Ipecacuanhic acid, C14H18O7, was obtained by Willigt (Annalen, 76, 345) from the roots of Psychotria ipecacuanha (Stokes), and consists of a reddish-brown, bitter hygroscopic substance. Its solution gives a green coloration with ferric chloride.
Japonic acid (see CATECHU).
Kino (see KINO).
Larch tannin. The bark of the larch, Larix europaea (DC.), contains considerable quantities of a tannin which was examined by Stenhouse (Phil. Mag., 23, 336). It forms an olive-green precipitate with ferric salts, and when boiled with dilute sulphuric acid a red phlobaphene is produced.
Maletto tannin occurs in the bark of Eucalyptus occidentalis (Endl.) and other species of eucalyptus. According to Strauss and Geschwender (Zeitsch. angew. Chem., 1906, 19, 1121) it possesses the formula (C43H50O20)2, and appears to be identical with quebracho tannin. Dekker (Arch. Neerland., 1909, ii., 14, 50) prefers the formula (C19H20O9)?, and describes the acetyl derivative C38H28O16Ac10 and benzoyl derivative C19H25O12Bz5. Heated with zinc-dust and sodium hydroxide solution the tannin gives small quantities of gallic acid and phloroglucinol, whereas dry distillation yields pyrogallol and traces of other phenols. Boiling dilute sulphuric acid forms "maletto red," C57H50O22 from which the acetyl derivative can be obtained.
Mangrove tannin, C24H26O12. This important tannin is derived from the Rhizophora mangle (Linn.), R. mucronata (Lam.), Ceriops candolleana (Arn.), C. roxburghiana (Arn.), and other allied species. It is described as an amorphous red powder, which on fusion with alkali gives protocatechuic acid, and with boiling dilute sulphuric acid the phlobaphene C48H46O21. The monacetyl derivative C24H25O23(C2H3O) melts at 205° (Nierenstein, Die Gerbstoffe). This tannin closely resembles in its properties catechutannic acid (see CATECHU), and indeed mangrove cutch and catechu may be employed in many cases for the same purpose. Possibly these two substances are identical, and Procter (private communication) has isolated from mangrove cutch a small quantity of a colourless crystalline substance resembling catechin. Perkin who examined an ethyl acetate extract of the fresh bark of the C. candolleana, prepared in Borneo, was unable to detect the presence of a catechin, but obtained the tannin as a pale yellow powder, which gave a green coloration with ferric chloride solution, and resembled catechutannic acid in many respects.
Mimosa tannin is derived from various species of Mimoseae, such as the Acacia arabica (Willd.) of Egypt, the so-called "Wattles" of Australia, and numerous others. The tannin present is interesting in that though it possesses the reactions of a phlobatannin, such as phlobaphene production, precipitation by bromine water and solubility of its lead compound in acetic acid, etc., it gives a bluish-violet coloration with ferric chloride. Ammonium sulphide gives a precipitate with a mimosa solution, when after removal of the excess by boiling, a few drops of sulphuric acid are added, followed by a small quantity of salt. All other phlobatannins, except Maletto and Pistaschia tannins, give no precipitate by this method (Stiansy, private communication).
Moritannic acid, see Maclurin.
Oxypinitannic acid, v. Pinitannic acid.
Oak bark tannin or Quercitannic acid is found in the bark of the oak, and is not to be confused with the tannin of oak-wood from which it is distinct, and which is described below under the name of quercinic acid. In 1792 George Swayne communicated to the Society of Arts his results on the use of oak leaves in tanning (Trimble, "The Tannins," ii., 51), and the subject was again discussed by Berzelius in his Lehrbuch, 1827, and by Liebig (Handbuch der Chemie, 1843). Assumed at that time to be identical with the tannin of nut-galls (gallotannin), it was first shown by Stenhouse (Phil. Mag., 22, 425) to differ from this substance. According to Grabowski (Sitz. Ber., 56, [ii.], 388), Oser (ibid., 72, [ii.], 178), Johanson (Arch. Pharm., [in.], 9, 210), Bd'ttinger (Ber., 14, 1598), quercitannic acid is in reality a glucoside, but Etti (Ber., 14, 1826; Monatsh., 4, 512) found that the pure substance did not yield a trace of sugar. Various formulæ have been assigned to this substance, viz. Eckert (Jahres., 1864, 608), C28H20O20; Oser (Jahres., 1875, 600), C20H20O11; Löwe (Zeitsch. anal. Chem., 20, 210), C28H30O15; Bottinger (Ber., 1883, 16, 2712), C15H12O9, 2H2O, and Etti (Monatsh., 10, 650), C17H16O9, C18H18O9, and C20H20O9.
Quercitannic acid is described by Etti as a reddish-white powder almost insoluble in water. One of its most characteristic properties is the readiness with which it forms reddish-brown anhydrides when heated by itself or with dilute acids. Thus at 130-140° the first anhydride, C34H30O17, is produced, and this by heating with dilute sulphuric or hydrochloric acid gives the second anhydride, C34H28O16, Boiling dilute sulphuric acid again converts the original tannin into the third anhydride, 2C17H16O9 3H2O = C34H26O15.
These compounds are insoluble in water, but colour a solution of ferric chloride blue (?). Löwe (loc. cit.) again examined an anhydride, C28H24O12, and an "oak red," C28H22O11. Bottinger, who prepared the oak red from the tannin by means of dilute sulphuric acid, adopted the formula (C14H10O6)2, H2O. Etti (Ber., 1884, 17, 1823) isolated from the bark of the Quercus pubescens (Willd.) a tannin C20H20O9, practically identical with the substance C17H16O9 previously found in the Q. robur (Linn.), but giving a green solution with ferric chloride, and not a blue, as formerly stated.
When heated with dilute sulphuric acid at 130-140°, quercitannic acid gives in addition to anyhydride 1,5 per cent, of gallic acid, and with strong hydrochloric acid at 150-180° the formation of oak red was accompanied by the evolution of methyl chloride (Etti, Monatsh., 1, 274). On dry distillation it yields dimethylcatechol and catechol, and on fusion with alkali protocatechuic acid, catechol, and phloroglucinol.
By the action of bromine on the aqueous bark extract, Bottinger (Ber., 1883, 1 6, 2710) obtained dibromquercitannic acid, C19H14Br2O10, as a yellow precipitate, and from this penta-acetyldibromquercitannic acid was prepared. Heated with hydrochloric acid at 180°, methyl chloride was evolved, and by means of hydroxylamine hydrochloride the compound C19H15Br2NO10 was produced. Reduced with sodium amalgam hydroquercinic acid, C15H18O7 or C15H16O6, and hydroquergalic acid, C14H14O6, are formed (Annalen, 263, 121). When suspended in chloroform and further brominated it yields tetrabromdehydroquerdtannic acid. Quercitannic acid was thus C19H16O10, contained five hydroxyls, and the group COCH8.
According to Etti (Monatsh., 10, 647) a further investigation of the tannins C17H16O9 and C20H20O9 has proved that they are not glucosides, but derivatives of a ketone acid, C6H2(OH)3.CO.C6H(OH)3COOH
Trimble ("The Tannins," 1894, ii., 77) carried out an elaborate investigation of the tannins present in the barks of the Quercus alba (Linn.), Q. coccinea (Wangenh.), Q. discolor (Ait.), Q.falcata (Michx.), Q. palustris (Du Roi), Q. prinus (Linn.), Q. bicolor (Willd.), Q. obtusiloba (Michx.), Q.phellos (Linn.), Q. rubra (Linn.), Q. robur (Linn.), Q. semicarpifolia (Sm.), employing acetone for the purpose of extraction. The tannins in most cases had a pale yellow colour, gave with ferric chloride a green coloration, and practically identical results with all the usual tannin reagents.
Heated with glycerol at 160, the tannins of Q. tinctoria, Q. palustris, Q. falcata, and Q. phellos yielded catechol, whereas with fused alkali the eight samples examined gave protocatechuic acid. Though all these compounds produce a violet colour on pine wood moistened with hydrochloric acid, phloroglucinol or other phenol was not detected among their decomposition products. Heated with 2 per cent, hydrochloric acid for two and a half hours, a phlobaphene separated, whereas the solution contained protocatechuic acid. Analyses of nine of these tannin preparations showed but little variation, the average being C = 59,79; H = 5,08, and approximately correspond with those of Etti (loc. cit.) for the tannin C20H20O9 from Q. pubescens, and of Kraemer (Amer. J. Pharm., 1890, 236) for the tannin of Q. alba.
Oak wood tannin, Quercin, Quercic acid, Quercinic acid, C15H12O9, 2H2O, consists of a light brownish-yellow substance, and is distinguished from the quercitannic acid of oak bark in that its aqueous solution gives a blue, not green, coloration with ferric chloride, and does not yield a precipitate with bromine water (Böttinger, Ber., 1887,20,761).
With the object of isolating the tannin in a pure condition, Bottinger acetylated a purified extract of the wood, and decomposed the acetyl compound C15H7(C2H3O)5O9 by heating it with water at 135°. By the action of sodium amalgam on the acetyl derivative, Böttinger (Annalen, 263, no) obtained hydroquercic acid, C15H18O7 or C15H16O6, querlactone, C5H6O2, and an acid which is probably trihydroxybutyric acid.
Hydroquercic acid is a grey-brown, bitter hygroscopic powder, which forms the acetyl derivative C15H14(C2H3O)2O6, the barium salt (Cl5H15Ofl ) 2Ba, and the lead salt (C15H15O6)2Pb. Querlactone, on the other hand, forms the salt (C5H7O3)2Pb. As above noted, hydroquercinic acid could also be obtained in a similar manner from qiiercitannic acid.
Etti (Monatsh., 10, 647) isolated from the wood of the Slavonian oak a tannin C16H14O9 which appeared to be a ketonic compound. This is present in the wood in the form of a readily soluble salt (probably magnesium salt). Crystallised from alcohol, it forms brownish-red microscopic warty spherical masses, insoluble in water, and having the properties of a monobasic acid (cf. Fuchs, Monatsh., 9, 1132). With phenylhydrazine it gives the compound C22H20N2O8, forms a brown amorphous oxime C16H15NO9, and with dilute sulphuric acid at 120-130° yields gallic acid in addition to a red anhydride. Heated alone at 130-135°, or in a sealed tube with water at 100°, anhydrides are also produced, which on boiling with hydriodic acid evolve methyl iodide. On long digestion of the tannin C16H14O9 with hydrochloric acid at 100°, a methoxyl group is split off, with production of a yellow coloured acid C15H12O9 in which a methoxyl group is still present. This tannin is therefore probably the dimethyl ether of the ketonic acid formulated above.
On boiling the tannin with dilute sulphuric acid, the anhydride C32H24O16 is produced, whilst on heating in a closed tube the anhydrides C32H20O14 and C32H18O13 were obtained.
The varied results of many of these workers with the oak tannins appear to be due, as suggested by Trimble, to the fact that in many cases they employed oak tannin extracts of doubtful authenticity. Thus it is possible that Etti, who in his earlier work describes the tannin as producing a blue coloration with ferric chloride, was in reality examining oak-wood and not oak-bark preparations, and again the peculiar insoluble property of certain of his tannins, also commented on by Trimble, suggests that in these cases he investigated an anhydride rather than the tannin itself. That oak barks contain a phlobatannin possessing a catechol nucleus appears to be certain from the investigations of Trimble, and it seems probable that in the wood either a pyrogallol tannin or a phlobatannin containing a pyrogallol group is present. Though, as stated above by Etti in the case of the Slavonian oak, this yields phlobaphenes, Stiasny (private communication) considers that such is not usually the property of oak-wood extracts. An interesting point, moreover, apparently not stated in the literature, though well known to tanners, is that oakwood extracts give some ellagic acid, and on this account impart to leather the "bloom" so characteristic of this substance.
Oenotannin, C19H16O10 (?), was obtained by Gautier from red wine (Bull. Soc. chim., 1877, 27, 496), who describes it as a colourless substance readily soluble in water. It gives a green coloration with ferric chloride solution, by fusion with alkali protocatechuic acid and phloroglucin, and when exposed to moist air becomes converted into an insoluble red phlobaphene-like substance. According to Heise (Ber. Ref., 22, 823), oenotannin contains gallotannin and is a mixture of three compounds.
Pistachia tannin is present in the leaves of the Pistacia lentiscus (Linn.) in addition to some quantity of a gallotannin (Perkin and Wood, Chem. Soc. Trans., 1898, 73, 378), and consists of a pale brown brittle mass which with iron alum solution gives a blue-black coloration. With boiling dilute sulphuric acid a phlobaphene quickly separates, and when fused with alkali, gallic acid and phloroglucinol are produced.
Phyllœscitannin is the name given by Rochleder to a tannin present in the small leaflets of the horse chestnut, as long as they remain enclosed in the buds (Zeitsch. fur Chem., 1867, 84). It is described as an amorphous red-brown substance of the formula C26H24O13, H2O, having a strongly astringent taste.
Pinicortannic acid and cortepinitannic acid occur in the bark of the Scotch fir, Pinus sylvestris (Linn.), and can be separated owing to the fact that in aqueous solution the former only is precipitated by means of lead acetate. Pinicortannic acid forms a reddish-brown powder of the composition (C16H18O11)2, H2O, which after drying is sparingly soluble in water. It gives a green coloration with ferric chloride, and when boiled with dilute acids gives the phlobaphene C48H50O21 (Kawalier, Sitz. Ber., 11, 361).
Pinitannic acid and oxypinitannic acid occur in the needles of the Scotch fir, Pinus sylvestris (Kawalier), and are distinguished from one another by the fact that the former only is precipitated by lead acetate solution. Pinitannic acid, according to Rochleder (Sitz. Ber., 2 9> 6p), also present in the Thuja occidentalis, is a reddish-yellow substance which gives a red-brown coloration with ferric chloride and when boiled with dilute acids a sparingly soluble red product (phlobaphene).
Oxypinitannic acid, on the other hand, yields a green solution with ferric chloride (Kawalier).
Quebracho tannin or Quebrachitannic acid, see QUEBRACHO COLORADO.
Quinotannic acid or Cinchonatannic acid obtained from cinchona bark is a light yellow very hygroscopic substance, a solution of which gives a green precipitate with ferric salts. On digestion with boiling dilute sulphuric acid, it is converted into a sugar and cinchona red C28H22O14 (Rembold, Annalen, 143, 270), and from the latter by fusion with alkali, protocatechuic and acetic acids are produced (Hlasiwetz, ibid., 143, 307). According to Schwarz (Sitz. Ber., 7, 250), quinotannic acid has the composition C14H16O9, whereas cinchona red is to be represented as C12H14O9.
Rhamnotannic acid (so-called), present in buckthorn berries, is in reality not a tannin matter.
Rhatany tannin, C20H20O9, from the bark of rhatany root. Krameria triandra (Ruis and Pav.), (Willstein, Jahres., 1854, 656) is described by Raabe (ibid.) 1880, 1060) as a light yellow powder, readily soluble in water. Its solution gives with ferric chloride a green coloration. When heated with dilute acids it yields rhatany red, C22H22O11, and a sugar (Grabowski, Annalen, 143, 274), whereas according to Raabe (loc. cit.) no sugar is thus produced and the red substance possesses the composition C20H18O8. By dry distillation rhatany red yields catechol, and protocatechuic acid and phloroglucinol when fused with alkali.
Rheotannic acid or Rhubarb tannic acid, C26H26O14, derived from rhubarb, forms a yellowish-brown readily soluble powder, the solution of which gives with ferric chloride a black-green precipitate. With boiling dilute acids it gives rheic acid (rheumic acid), C20H16O9 and a fermentable sugar (Kubly, Zeitsch. fur Chem., 1868, 308), although according to Tschirch and Neuberger (Schweiz, Wochenschr. Chem. Pharm., 1902, 282) in this manner rheum-red, C40H32O18, cinnamic acid, gallic acid, and sugar are produced. According to Gilson (Chem. Zentr., 1903, i., 722, 882), two glucosides are present, glucogallin, C13H16O10, giving gallic acid and dextrose, and tetrarin, C32H32O10, from which rheosurin, C10H12O2, cinnamic acid, and gallic acid can be produced. According to Krembs (Inaugural Diss., 1903, Berne), a catechin is also present in rhubarb.
Rhodotannic acid, 4C14H12O7, 3H2O, found in the leaves of Rhododendron ferrugineum (Linn.), is an amber-coloured substance which gives a green coloration with ferric chloride solution. Heated with dilute mineral acids, a reddish -yellow precipitate of Rhodoxanthin, C14H14O8, is produced (Schwarz, Sitz. Ber., 9, 298).
Rubinic acid, v. CATECHU.
Rubitannic acid, 2C14H22O12 + H2O, was obtained by Willigt (Annalen, 82, 340) from the leaves of Rubia tinctorium (Linn.). It gives a green colour reaction with ferric chloride.
Sequiatannic acid, C21H20O10, was isolated from the cones of Sequoia gigantea (Torr), (California), by Heyl (Pharm. Zentr., 1901, 42, 379) as a reddish-brown powder, soluble in water and yielding the salts MgC21H18O10 and CaC21H18O10. Boiled with dilute sulphuric acid, a phlobaphene, gallic acid, and a sugar are produced. The hexa-acetyl, C21H14O6(C2H3O)6, hexabenzoyl, C21H14O10(C7H5O)6, and bromine, C21H15O10Br5, derivatives of this tannin are amorphous.
Sorbitannic acid, from the juice of the ripe berries of the mountain ash, Sorbus ancuparia (Linn.), forms a thick syrupy mass, which gives a green coloration with ferric chloride solution. It yields catechol on dry distillation, and protocatechuic acid and phloroglucinol when fused with alkali (Vincent and Delachanal, Bull. Soc. chim., [ii.], 47, 492).
Spruce-bark tannin, C21H20O10 (?) gives, according to Bottinger, an unstable bromo derivative C21H14Br6O10. This reacts with hydroxylamine hydrochloride, and with hydrochloric acid at 180-190° evolves methyl chloride. The penta-acetylpentabromo derivative C21H10Br5O10(C2H2O)5 was also prepared. With boiling dilute hydrochloric acid the tannin yields spruce red which gives the acetyl derivative C42H27(C2H3O)7O17 and when suspended in chloroform and treated with bromine the compound C42H24Br10O17 (Bottinger, Ber., 17, 1127).
Strawberry-root contains a tannin fragarianin (Phipson, Jahres., 1878, 891), the solution of which gives a green colour with ferric chloride. Boiling dilute hydrochloric acid forms glucose and a red substance fragiarin. On dry distillation the tannin gives traces of catechol, and when fused with alkali protocatechuic acid is produced.
Tannecortepinic acid, C28H26O12, according to Rochleder and Kawalier (Sitz. Ber., 29, 23), can be isolated from the bark of young Scotch firs collected in the spring time. Ferric chloride gives a green coloration and boiling dilute acid a phlobaphene in addition to a little sugar.
Tannopinic acid, C28H30O13 (?) is sometimes present in the needles of the Scotch fir gathered in the spring (Rochleder and Kawalier). In the winter time, oxypinitannic acid (loc. cit.) appears to take its place.
Tea tannin is probably identical with the quercitannic acid of oak bark (Stenhouse, Phil. Mag., 23, 332; Rochleder, Annalen, 63, 205; and Hlasiwetz and Malin, J. pr. Chem., [i.], 101, 109).
Tormentilla tannin, C26H22O11, from the root of Potentilla tormentilla (Neck.), is an amorphous reddish powder, which colours ferric chloride solution blue-green. Boiled with dilute acids it produces tormentil-red without appreciable formation of sugar, and this appears to have the same composition as the tannin itself. With fused alkali phloroglucinol and protocatechuic acid are obtained. The root also contains a substance which yields ellagic acid when boiled with potash solution (Rembold, Annalen, 145, 5).
Viridic acid, C14H20O11 (?), which exists in coffee beans as a calcium salt (Rochleder, Annalen, 63, 197), is obtained by the air oxidation of an ammoniacal solution of caffetannic acid, and forms a brown amorphous mass, the alkaline solutions of which are green. The salts, Ba2C14H16O11, PbC14H12O8, and PbCuH14O9, have been described (cf. also Vlaanderen and Mulder, Jahres., 1858, 261).
Willow bark tannin. The bark of Salix triandra (Linn.) contains a glucoside tannin which gives a green colour reaction with ferric chloride, and when boiled with dilute sulphuric acid a brownred precipitate (Stenhouse, Proc. Roy. Soc., u, 403; Johanson, Arch. Pharm., [iii.], 13, 103).
Tannins are frequently accompanied in the plant by yellow colouring matters, and it has been pointed out by Perkin that a relationship is usually to be observed between these compounds in respect of the phenolic nuclei present in each. Thus catechu contains catechutannic acid and quercetin, both of which contain phloroglucinol and catechol groups, whereas both the cyanomaclurin and morin of Jakwood (Artocarpus integrifolia, Linn.) yield phloroglucinol and β- resorcylic acid. Again, in sumach (R. coriaria, Linn.), Pistacia lentiscus, Linn, (leaves) and Hæmatoxylon campeachianum, Linn, (leaves), a gallotannin and myricetin exist, both of which are pyrogallol derivatives.
Other similar instances of this relationship could be cited; and where a divergence of this rule at first sight seems evident, this is frequently more apparent than real, as in the case of Young Fustic (R. cotinus, Linn.), which is known to contain a gallotannin and fisetin (catechol and phloroglucinol). From the reactions of the wood extract, however, catechol tannin must also be present.
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