ANALYTICAL EDITION
January 15, 1943
At the end of a reflux period of 50 minutes the liquid contents
of the absorption tubes are transferred to a 50-cc. Erlenmeyer flask with ethanol (95 t o 100 per cent). The crystalline residues
left in the first and second absorption tubes are then washed with 2-cc. portions of water to dissolve the crystals of tetramethyl ammonium iodide adhering to the glass, then with two subsequent portions of ethanol. The combined absorption solutions plus washings are allowed to stand for a t least 3 hours a t room temperature. A small boiling chip of porous plate is then added to the flask and the contents are evaporated almost to dryness on a steam bath, or by use of a hot plate (if carefully watched to prevent complete evaporation with resulting decomposition of the quaternary iodides). Complete drying is effected by leaving for 12 hours in a vacuum desiccator containing calcium chloride. The trimethylethyl ammonium iodide is then extracted as follows: A 3-cc. portion of a filtered, saturated solution of tetramethyl ammonium iodide in absolute ethanol is added to the flask by means of a medicine dropper pipet. (If absolute ethanol alone is used as extractant, a correction of 0.2 cc. of thiosulfate for 9 cc. of ethanol extractant must be added to the quantity of thiosulfate used in the titration.) After the mixture has been shaken gently for about 1 minute, the crystalline product is allon-ed t o settle on one side of the tilted flask and the supernatant liquor is transferred to a glass-nail suction filter by means of a second pipet. This treatment is repeated twice. After the final decantation the transfer pipet is dried free from ethanol in a slow current of air, and the traces of tetramethyl compound are dissolved in distilled water. The aqueous solution is placed in a second flask, which also contains the air-dried filter paper. The residual contents of the original Erlenmeyer are freed from traces of ethanol in a vacuum desiccator. After 1 to 2 hours of this vacuum treatment, the aqueous contents of the second flask are transferred to the original flask, and the aqueous solution of tetramethyl ammonium iodide is then ready for volumetric determination. The aqueous solution of the quaternary ammonium iodide is treated with 10 cc. of a saturated glacial acetic acid solution of potassium acetate containing 8 to 10 drops of bromine for 2 to 3 minutes, followed by the addition of 5 cc. of 25 per cent aqueous sodium acetate. The bromine is reduced with 10 drops of formic acid (80 to 90 per cent) and the resulting clear solution then treated with 5 cc. of 10 per cent aqueous potassium iodide solution and 5 cc. of 10 per cent sulfuric acid. The liberated iodine is titrated with standard (0.05 N ) thiosulfate, using starch solution as an internal indicator.
TABLE 11. METHOXYL-ETHOXYL AXALYSES Compound Vanillin Vanillin Vanillin p-Ethoxybenzoic acid p-Ethoxybenzoic acid 3-Ethoxy-4-methoxybensoic acid 3-Ethoxy-4-methoxybenzoic acid 3-Ethoxy-4-methoxybenzoic acid 3-Ethoxy-4-methoxybenzoic acid 3-Ethoxy-4-methoxybenmoic acid 3-Ethoxy-4-methoxybenzoic ocid 3-Ethoxy-4-methoxybenzoic acid 3-Ethoxv-4-n~ethoxybenzoicacid a-Ethoxypropiovanillone (I) Me0 H
Found OMe OEt 20.2 0.1 20.1 0.2 20.3 0.0 0.0 27.0 0.0 27.2 15,s 23.0 15.7 22.9 15.9 23.1 15.8 23.0 16.0 23.2 15.9 23.1 16.0 23.2 15.7 22.9 13.7 20.2 13.6 20.3 13.7 20.2
Calculated OMe OEt 20.4
0.0 -
0.0 -
27.2
-
15.8
23.0
-
-
-
-
13.8
20.1
-
25
Table I1 includes the results obtained by this procedure with certain reference compounds.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 5th ed., p. 177 (1940). (2) Friedrich, 2. phusiol. Chem., 163, 141 (1927). (3) Phillips and Goss, J . Assoc. Oficial A g r . Chem., 20, 292 (1937). (4) Viebock and Brecher, Ber., 63,3207 (1930) ( 5 ) Viebock and Schwappach, Ibid., 63, 2818 (1930). (6) Killstatter and Uteinger, Ann., 382,148 (1911). (7) Kilson, J . Assoc. Oficial A g r . Chem., 18,477 (1935). (8) Zeisel, Monatsh., 6, 989 (1885); 7, 406 (1886).
Recovery of Solvents Used in the Chemical Determination of Thiamine MORTON PADER, Food Research Laboratories, Inc., Long Island City, N. Y.
HERE routine thiamine determinations are run by either the thiochrome method (1) or, t h e colorimetric procedure ( 2 ) i t is practical, and at t h e present time advisable, to recover the solvents, isobutanol in t h e former case and xylene in t h e latter. T h e distillation procedure generally used is tedious and requires attention, precautions must be observed t o minimize fire hazards, and fluorescent materials in the isobutanol are not always coinpletely removed. T h e author has obtained isobutanol with blank readings much lower t h a n those usually obtained b y distillation in an all-glass soill by treating waste solvent, containing thiochrome and other fluorescent materials, with activated vegetable charcoal (Darco-G-BO, obtained from t h e Darco Corporation, 60 East 42nd St., New York, N. Y.). The isobutanol recovered in this manner has been used repeatedly in determining thiamine i n a large variety of biological materials. Technical grade isobutanol, which usually contains fluorescent substances, may also be treated in this manner. T h e recovered isobutanol has proved to be as satisfactory in every respect as t h e solvent redistilled i n all-glass apparatus; it fails to give rise t o fluorescent substances on standing or after treatment with alkaline potassiclm ferricyanide or with alkali alone, according t o t h e procedure for t h e estimation of thiamine.
-
The isobutanol, ,previously dried in the course of the assay, is recovered by shaking 100 cc. of solvent with 1.5 grams of activated charcoal for 15 to 30 minutes. This ratio of adsorbent to solvent is optimal, but equally good results are obtained by using an excess of charcoal-about 5 grams per 100 cc.-and shaking for only a few minutes. The charcoal suspension is then clarified by filtration. The filtrate, free from any fine particles of adsorbent, is used without further treatment.
T h e methoxyl and ethoxyl contents are calculated according t o t h e following equations:
In t h e Jfelnick-Field method for the determination of thiamine ( 2 ) t h e red color of t h e xylene solution is subjected to colorimetric evaluation. Here also, the solvent may be decolorized by the addition of activated charcoal, filtered, and used again.
-
-
(normality of thiosulfate) (zOhle = (cc. of thiosulfate)6 XX (sample weight) alkoxy1 as OMe) - (% Ohle) 31
X 31
] x 45
The red dye complex in xylene appears to be adsorbed to the charcoal even more readily than the thiochrome from isobutanol solution. About 1 gram of charcoal is added to 100 cc. of the pigmented xylene solution and the suspension shaken for 5 minutes; this yields a colorless filtrate.
Discussion of Results Table I indicates t h a t all the methyl iodide is collected when three receivers are used and t h a t the yield of tetramethyl ammonium iodide ib not affected by t h e ethanol extractioii.
Literature Cilecl (1) (2j
Hennessv. D. J.. IXD.ESG. CHEM..A N . ~ L .ED., . 13.. 216 (1941) Ifelnick: D., a n d Field, H., J r . , j . B i d . Chem., 127, j b 5 , 515, 531 (1939).
