Sept., 1912
The amount of total amyl alcohols, which, industrially, is t h e chief point, shows a diflerence of only 0.15 per cent. The respective figures for butyl alcohols differ b y 3 ~ 7 6per cent., though t h e propyl closely corresponds. This is. however, of little importance, as it shows only t h a t one sample of oil was’ washed more t h a n tbe other. TElsrorcro,
CHEMISTRE’.
T H E J O C R S A L OF I.YDc‘STRIAL A-VD EA-GISEERISG
ChXhDA.
669
added, and diluted t o jo cc. with water. No difference in color could be noticed among the three and they showed about I / ~ the color of a sample of four cc. of t h e 0.05 gram in I O O cc. sol. not treated with lead! cream. Inasmuch as lead sulphate was precipita’te’d out when the ferrous sulphate and bi-omine tvereadde3 i.t was thought possible th’at thlis pskcipitate mecKan!-’ c.ally cafried down somie vanlillid. Since vanilla contains srriall an-ioudts oi ox&. acid! and phosphates, 4 cc. of vadillin staddard ( 0 . 0 5 in; IO@) was treated with 5 drops of 85 per cent. phosphoric, acid and then wlth lead cream. I t was not necessary t o centrifuge as the lead agglutinated immediately, and on the addition of the ferrous sulphate and bromine water no precipitate was formed. The solution matched up t o a standard untreated with lead except t h a t i t was of a purplish color. But if four drops of phosphoric acid were used instead of five, a precipitate was formed on the addition of bromine water and ferrous sulphate and the color did not match an untreated standard. A series of experiments were carried on in the same manner with malic acid instead of phosphoric, and it was found t h a t 0.5 cc. of a I O per cent malic acid gave the best results ; the solution had the characteristic bluish green color instead of being purplish as with the phosphoric acid. On standing four weeks, the samples acquired a yellowish tinge in comparison to freshly prepared samples. I n the original method of MoerkI a few drops of ferrous sulphate are added and then t h e bromine drop by drop t o a maximum color. I n the method of the government, however, an excess of bromine is added and sufficient ferrous sulphate t o produce the maximum color. A number of experiments were carried out t o see if i t made any difference which way i t was done and t o find the limit in amount of ferrous sulphate and bromine water if any. One cc. of standard vanillin solution (0.05 in 100) was used in all cases. I
DIFFICULTIES IN THE COLORIMETRIC ESTIMATION OF VANILLIN. Uy \V. S. HUBBARI). Received July 19, 1912.
hloerk,? in 1891, found in testing for vanillin t h a t he had some difficulty in always obtaining the ferric chloride color reaction, and tried using a ferrous salt and oxidizing i t with bromine water. I n the latter case, he found the color much more intense than with ferric chloride and was able t o detect‘ I : I O O , O O O instead of I : 2 , 0 0 0 as before. I n a paper3 a month later he proposed a colorimetric estimation of vanillin in vanilla extracts by this means and his method with a few modifications was later adopted by the Bureau of Chemistry.4 The procedure is as follows: “Measure 2 cc. of the vanilla extract into a test tube and add about j cc. of lead hydrate; mix thoroughly, pour upon a small wet filter, collect filtrate and washings in a jo cc. graduated Kessler t u b e ; add a n excess of bromine water ( 3 or 4 drops) and sufficient freshly prepared I O per cent. ferrous sulphate solution t o produce the maximum bluish-green color t h a t will result if vanillin is present, a n d fill t o the mark with water .’ ’ “Compare with solutions containing a known amount of vanillin treated as directed above.” The lead hydrate is prepared as follows: “Dissolve 2 0 0 grams of lead acetate in 850 cc. of water, filter and add an excess of potassium hydroxide. Let the precipitate settle and wash thoroughly b y decantation with repeated portions of water until perfectly neutral. Keep in j o o cc of water in the reagent bottle, and shake t o form an emulsion-like mixture before adding t o decolorize.”,, The above method has been used in this laboratory with indifferent success for the past two years. Not until this year were the standards p u t through the treatment with lead hydrate as is directed in the method: then the troubles quickly multiplied. I t was noticed t h a t i t was not always possible t o match two standards containing the same amount of vanillin and treated in a like manner. An attempt was made t o locate the trouble by means of a number of experiments. Four cc. each of three solutions of vanillin standard made up according t o t h e directions given in Bulletin 1 0 7 , but containing o . o j , 0 . 1 0 and 0 . 2 0 gram o f vanillin per I O O cc. respectively, were treated with lead cream, centrifuged and filtered, ferrous sulphate and bromine Read a t the February meeting of University of Michigan Section of the:.%. C. S.y I wish to thank Dean J ,0 . Schlotterbeck for his interest in my work. Am. J . P h a ~ v r .63, , 521. i Ibid.. 572. Hir//. 107, (r
.i 2
5
5 4
5 5
5 6
5 7
5 8
Drops Br sol. Drnps FeSO, sol.
1
3
,
h-o color
Darkest and equal
._-_--
Lighter and e r i u a l
I t was found t h a t after obtaining the maximum color in the above tests and then diluting t o jo cc. with water, it was necessary in every case t o add at least 2 drops more bromine water t o bring the color up to a maximum, a n d this could not be accomplished by adding t h e extra 2
A m J . P h a r n , , 63, 5 2 1 .
T H E J O C ' R N A L OF I N D U S T R I A L A N D E S C / , Y E E R I i Y G CHEJllSTRY.
6j o
2 drops of. bromine water before diluting. When the bromine water was added first and the color developed with ferrous sulphate and diluted, a deeper color could not be obtained by the additipn of more bromine water (Table 111). I t was noted too that those which had a larger proportion of ferrous sulphate gave the deeper color, a fact also noted by Fluckiger and Nagelwort.' I n those in which the bromine was added first (Table 111) the color was not nearly as deep as in those in which ferrous sulphate was added first (Table I ) . I t was found t h a t i t took 2 . 5 cc. of the vanillin solution ( 0 0 5 in 1 0 0 ) when bromine water was added first, t o equal I cc. when ferrous sulphate was added first. One cc. of pyrocatechuic acid (equivalent to the one cc. of vanillin) and 2 drops of ferric chloride added gave the same depth of color as I cc. of vanillin when treated with ferrous sulphate and bromine water. CarlesZ in 1 8 7 2 and Tiemanna and Haarmann in 1874 showed t h a t a water solution of vanillin gave a precipitate, soluble in hot water, with a concentrated solution of lead acetate. The lead salt has the formula (C,H,O,),Pb. I n trying lead acetate and also lead nitrate solutions we were unable t o get any precipitate with a water solution of vanillin of the strength usually met with in extracts. When, however, the clear, neutral filtrate from lead cream was added to the vanillin solution there appeared immediately a yellow precipitate. This precipitate when dissolved gives the color with ferrous sulphate and bromine water. Some of the yellowish precipitatewas extracted with ether and the ether evaporated, leaving a crystalline mass which responded to the vanillin color reaction. On standing I 2 - 2 4 hours, colorless, rosette like crystals formed in the filtrate from which the yellow precipitate was filtered out. The crystals were soluble in hot water and when massed together in some quantity had a yellow color similar t o the first precipitate. . A number of analyses were made of the precipitate which comes down immediately and were as follows: The precipitate was dissolved in a little dilute acetic acid and hydrogen sulphide passed in, the lead sulphide washed, dried and weighed as such.
RESULTS.
Wt. of lead vanillin. Gram. Theoretical. A B C D
E F
0.357 0.09695 0.1238 0.0946 0.1130
Wt. of PbS. Gram.
.. 0.0626 0,0858
0.0732 0,0864
... 0.0642
Pb(QH?Os)2.
.. 0.0370 Average.
Pb. 1.724 1.771 1.666 1.48 1.50
..
1.98 1.687
The filtrate from the lead showed a strong color reaction for vanillin. CONCLUSION.
I n the official colorimetric estimation of vanillin in vanilla extracts, i t is difficult t o get a maximum color. The original method of adding the ferrous sulphate 1 2
3
"Reactions." p. 152. by Fluckiger. soc. cham., 17, 2. Rer Chem. Geos.. 1, 614.
Bull.
Sept., 1912
first gives a deeper color than that of the present method when the bromine is added first. I n a vanilla extract i t is very difficult to add only enough lead cream t o decolorize the solution and when different amounts of lead cream are used different depths of color are obtained. Dilution of the sample influences the color. It is shown t h a t much 'arger amounts of ferrous sulphate are necessary in comparison with bromine water t o produce a maximum color. I t is shown that the lead cream forms a lead vanillin compound of the formula (C,H,O,),Pb and such being the case a quantitative estimation is impossible where lead is used. I t seems quite likely that the vanillin is oxidized to pyrocatechuic acid. DEPARTMENT OF FOODAND DRUGANALYSIS, SCHOOL O F PHARMACY,UNIVERSITY OF MICHIGAN, ANN ARBOR.
A NEW COLORIMETRIC METHOD FOR THE DETERMINATION OF VANILLIN IN FLAVORING EXTRACTS. B y OTTO FOLINAND W. DENIS. Received July 1, 1912.
As the Hess-Prescott method for the determination of vanillin, which in the mo'dified form proposed by Winton and his associates' is now universally used in American food laboratories, is extremely laborious, although undoubtedly accurate, i t has seemed worth while t o attempt t o work out a rapid colorimetric method for use in this determination. The time spent a t present b y the food analyst on the quantitative determination of vanillin in flavoring extracts is out of all proportion t o the value of the results when judged by the weight given them in passing judgment on the quality of commercial extracts. By the use of the phosphotungstic-phosphomolybdic reagent recently described2 we have been able t o work out a colorimetric method for the determination of vanillin which gives theoretical results with purely artificial extracts containing known amounts of the substance, and gives with authentic extracts values agreeing closely with those obtained by the official method. Solutions Required.-( I ) An aqueous solution of pure vanillin t o be used as a standard. This should be made of such a strength t h a t I O cc. contains one mg. of vanillin. ( 2 ) The phosphotungstic-phosphomolybdic acid reagent, prepared as follows: To 100 grams pure sodium tungstate and 20 grams phosphomolybdic acid (free from nitrates and ammonium salts) add I O O grams syrupy phosphoric acid (containing 85 per cent. H,PO,) and 7 0 0 cc. water; boil over a free flame for one and a half to two hours; then cool, filter if necessary, and make up with water to a volume of I liter An equivalent amount of pure molybdic acid may be substituted for the phosphomolybdic acid. (3) A solution of pure sodium carbonate saturated a t room temperature. 1
2
ai,
J . A * ~ .them. sot.. 256 (1899); a4, 1128 ( 1 9 0 2 ) ;27, 719 ( 1 9 0 s ) . J . 1 3 d Che7n., 12, 239 (1912).
