September, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
925
Quinone Tannagelp2 By Arthur W. Thomas and Margaret W. Kelly COLUMBIA UNIVERSITY, NEW YORK, N. Y.
T
Quantitative studies of the combination of quinone with hide subCalling the solutions used H E ability of benzostance, forming leather, show that the rate of tanning is a function of forthe ext~emesof PH “bufquinone to combine Wh gelatin and COlfers” is admittedly questhe p H of the solution. The tanning action of quinone is manifested lagen and to Convert them tionable, but, owing to the in alkaline solutions, and the rate is greatest at p H 8 and IO. Hydroquinone retards the tanning action, indicating the, calidity of Possibility of confusion in to insol.uble substances was shown by hfeunier.3 He Meunier’s theory of quinone tannage. The results obtained offer results due to use of difa suggestion for the tanning action of commercial vegetable tanning ferent standard buffer comfound quinone to be a reextracts in solutions on the alkaline side of the isoelectric point of binations, it was decided to markable tanning agent, the leather formed by it being collagen. keep the chemical composiunaffected by boiling water. tion of the s o l u t i o n s a s Owing to its cost, as a tannearly similar as possible. ning agent it is of immediate theoretical rather than of pracTABLE I-SOLUTIONSEMPLOYED tical interest. Since the organic chemistry of the complex PH commercial vegetable tannins is only in its initial stages, it 1.0 Approximately M / 2 HaPo4 2.0 Approximately M/50 Hap04 seems that the study of any simple organic substance having 3.0 Ap roximately M/1000 Hap04 4 . 0 M A 5 KHzP04 and M / 1 0 Hap04 tanning properties should help elucidate the chemistry of the 5.0 Mixture of 44/15 KHzPO4 and M/15 NapHPOI act,ion of the very complex natural tannins. Meunier’s experiments were qualitative only. No quantiMixtures of M / l 5 KHzPOI and M/15 N ~ P H P O ~ 8.5 tative studies have been previously undertaken, possibly M / l 5 NazHPOa 9.0 because a satisfactory method was unavailable. Quinone 9.5 tannage is not amenable to the ‘(by difference’’ technic as Mixtures of M/15 NazHPO4 and M / 1 0 NaOH 12.0 ordinarily used to estimate the amount of tannin combined with skin substance. The reason is that quinone is about as TECHNIC volatile as water. Moreover, titration of quinone in the rel k t i o n s of 2.74 grams of quinone were placed in widesidual liquors fails, owing to the dark-colored products formed in alkaline solutions. The new Wilson and Kern method4 mouthed pint bottles. TWOhundred-cubic centimeter porof determining tannin fixed has solved this problem. The tions of the buffer solutions were added. When the quinone writers have found that the fixation of quinone by collagen can had dissolved, Portions of defatted hide Powder wJa1 to 2 grams of absolutely dry substance were added. The bottles be followed by this method. Since it has been demonstrated that the rate of fixation of were then stoppered and rotated a t room temperature. vegetable tannins by collagen varies enormously with the At the end of the time selected, the contents of the bottles hydrogen-ion concentration of the solution,5 the fixation of were transferred to Wilson and Kern extractors and washed quinone as a function of the pH value of its solution was therein with distilled water until no reaction for quinone was obtained by means of the starch-iodide test. This test, as investigated first. employed, was delicate to 1part of quinone in 50,000 of water. The tanned samples were then air-dried, after which they were EFFECT OF PH dried in vacuo at 110’ C. for 16 hours. They were then The quinone used was purified by sublimation or by crys- weighed, the increase in weight being taken as “quinone fixed.” The fixation Over Periods of 6 hoUrSl 24 hours, 2 weeks, and tallization from gasoline. Since Nelson and Granger6 found the solubility in water to be 1.37 grams per 100 cc. of solution 5’/1 weeks has been determined. a t 25’ C., this concentration was used in all experiments reT A B b E 11-FIXATION OF QUINONE IN 6 HOURS ported herein. The ordinary method of electrometrically Increase in t.itrating the solutions to definite pH values cannot be apweight of 2 CHARACTER OF grams dry plied to solutions of quinone owing to its ready reduction to Pl-1 of SOLUTION WITH CHARACTER OB W E T hide powder Gram hydroquinone, and consequently buffer mixtures were em- No. solution DISSOLVED Q U I N O N E T A N N E D POWDER Loss ployed to give the p H desired, as described in Table I. Un1 1 ,o Orange-yellow, clear Gelatinous white 0.103 0.083 necessary detail concerning the exact concentrations of reaE:::!; ;‘!tE; ,!+i;:i;:z;i ,Wa,i,ttsh 0 . 0 3 0 gents it; omitted, since no attempt was made to duplicate 4 4.0 Wine color clear Gelatinous, reddish 0.029 5 5.0 R‘ine color: clear Gelatinous. reddish 0.012 standard buffer tables. The buffer reagents were made up and Gain mixed in proportions, determined by electrometric titration, 6 6.0 Dark brown muddy Well tanned blackish o , 107 7 7 . 0 Dark brown: muddy Well tanned: blackish 0 .236 t o give the pH desired. 8 8.0 Dark brown, some
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3”::
1 Presented by Miss Kelly before the Division of Leather Chemistry a t the 66th Meeting of the American Chemical Society, Milwaukee, Wis., September 10 to 14, 1923. 2 Contribution No. 451 from the Chemical Laboratories, Columbia University. a Compl. rend., 146, 987 (1908); Collegium, 1908, 195; 1909, 58, 319; 1914, 523; Cuir, 3, 465 (1914). 4 THISJOURNAL, 13, 772 (1921). 5 Thomas and Kelly, I b i d . , 15, 1148 (1923). a Granger Dissertation, Columbia University, 1920.
9
11 12
Et;:
precipitate Dark brown, some precipitate Dark brown, precipitate 11.0 Dark brown, slight precipitate 12.1 Greenish black, no precipitate Tests on the filtrates showed 9.0
Well tanned, hlackish
0.402
Well tanned, blackish
0.399
Well tanned, blackish
0,420
Well tanned, blackish
0.408
Well tanned, blackish 0.314 quinone present in all cases.
When the samples were dried, all were dark in color: Nos. 1 ,,and 2 showed pronounced evidence of hydrolysis; 3 ,
INDUSTRIAL A N D EN(XNEERING CHEMISTRY
926
4, and 5 were dark brown, while 6 to 12 were blackish and of
good texture. Although 3, 4, and 5 showed loss in weight, the color indicated some fixation of quinone. Determination of nitrogen in the filtrates showed the following percentages of hydrolysis of the hide powder: No.
Per cent hydrolyzed
PH
No.
pH
Per rent hydrolyzed
The results shown in Table I1 are plotted in ,Fig. I along with those for the longer time intervals. In the longer time interval experiments, acidities greater than pH = 5 were omitted, b u t since fixation was evid e n t a t pH = 12, pH = 13 was included, as shown in Table 111. FIG. 1
TABLE 111-FIXATION O F QUINONE I N 24 HOURS, 2 WEEXS, AND,5'/7 WEEKS INCREASE IN WEIGHT OF 2 GRAMS D R YHIDEPOWDER PH 24 Hours 2 Weeks 51/7 Weeks 5.0 0,056 0,908 1.089 6.0 0.170 0,868 1.028 7.0 0.540 0.915 0.980 8.0 0.587 0.947 0.964 8.5 0.919 0.860 9.0 0 : 607 0.811 0:851 9.5 0,596 0.887 0.973 !0.0 0.658 0,938 0.966 -1.0 0.636 0 893 0.937 12.0 0.416 0.587 0.817 13.0 Loss of 0.303 Discarded Discarded
-No. 1 2 3 4 5 6 7 8 9 10
I1
Vol. 16, No. 9
The oxidized collagen combines with part of the remaining quinone. All the filtrates in the experiments described above reduced Fehling's solution, indicating the presence of hydroquinone. More specific tests for hydroquinone failed owing to the dark color of the filtrates. Since indication of the validity of Meunier's theory was found, it was considered possible to subject it to a inore conclusive test. If hydroquinone is formed during the tanning, then the addition of hydroquinone should repress the tanning action of quinone. The addition of hydroquinone to quinone solutions results in the formation of the qddition compound, quinhydrone, but since this compound dissociates partially into its constituents in aqueous solution, the formation of quinhydrone should not produce any complications. Hide powder was drummed as before with quinone solutions of the same concentrations but with different amounts of hydroquinone present. The experiment was carried out in two series, one in a buffer a t pH = 7 and another at pH = 9, and the time was 6 hours. IV-EFFECT OF HYDROQUINONE ON QUINONE TANNAGE Hydroquinone INCREASE IN WEIGHT OF 2 GRAMS DRYHIDE POWDER present At pH = 7 At pH = 9 Grams Gram Gram None 0.323 0.454 0.309 0.433 1.0 0.247 0.416 2.0 0.251 3.0 0.302 4.5 0.166 0.181 6.0 0.115 0.106 TABLE
~~
~~
These data are shown graphically in Fig. 2. The presence of hydroquinone reduces the tanning action of quinone. It is more marked at pH = 9, and also when the amount of hydroquinone equals and exceeds the amount of quinone present, where the latter is in the form of quinhydrone.
All filtrates showed positive tests for quinone. Some of the filtrates in the 24-hour series were subjected to the Kjeldahl determination. The degree of hydrolysis of the hide substance so found is shown below. No. 1 3 6
PH
*5 . 0
7.0 9.0
Per cent hydrolysis 2.9 2.5 1.8
No. 9 10 11
PH 11.0 12.0 13.0
Per cent hvdrolvsis
2.i
2.2 20.0
The high degree of hydrolysis in the solution of pH = 13 shows the futility of studying the fixation beyond pH = 12. The data are plotted in Fig. 1. I n the 6-hour period a slight fixation is noted at pH = 5, which rapidly rises to pH = 8 and r e m a i n s f a i r l y constant until pH = 11, except for a slight depression at 9 followed by a slight rise - 1 Q 0o I z 3 4 5 6 at 10. Theresult obGrams of Hydroquinone Added tained in 2 weeks is FIG.2 striking with its marked depression at pH = 9. In solutions more alkaline than pH = 9, it is quite possible that the nature of the substance acting as a tannin is different from that in the less alkaline solutions, owing to polymerization and other changes in quinone in alkaline solutions. Meunier believes that, in tanning by quinone, quinone first oxidizes the collagen as it does aromatic amines. As a result of this oxidation of the collagen,hydroquinone is formed. .R:
D
FIG.3
SPEEDOF FIXATION The speed of fixation of quinone in solutions at pH = 8, using 200 cc. of solution containing 2.74 grams quinone and portions of hide powder equal to 2.000grams dry substance, was determined at 25' C. The rotating machine containing the bottles was immersed in a water thermostat at this temperature. The data in Table V and Fig. 3 show a smooth curve of parabolic shape, which, however, when submitted to calculation by the monomolecular and dimolecular laws, showed that the reaction was of higher order. TABLEV-RATE
Time Minutes 18 32 60 91 121 210
QUINONETANNAGE AT PH = s AND AT, 25' C . Increase in Increase In weight of 2 weight of 2 grams hide grams hide powder Time powder Gram Minutes Gram 0.094 300 0.878 0.126 420 0.418 0.180 600 0.496 0.211 1440 0.616 0.254 14296 0.835 0.333 24500 0.947
OF
The authors are pleased to acknowledge the generous support of A. F. Gallun & Sons Company in this investigation.
