DECEMBER 15, 1938
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.4IVALYTICAL EDITION
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Summary -276‘
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e f r a c t l v a Index
The advantages of fractional extraction following fractionation by distillation in the separation of very complex mixtures of closely r e lated compounds like those found in petroleum acids are stressed. Two rotary columns for countercurrent extraction with or without reflux are described. Results obtained in the separation of caproic and n-heptylic acids and of a complex petroleum acid mixture are presented.
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Literature Cited
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(1) Evans, H. M., et al.,
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IXD. EXG.CHEX, 26, 3 9 i
(1934). (2) Jantaen, Dechema .Monograph, 5’01. 5, “Das
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frak-
tionierte Destillieren und das fraktionierte Verteilen als Methoden zur Trennung von Stoffgemischen,” Berlin, Verlag Chemie, 1932. (3) Keyes, IND.EKG.CHEW.., 25, 358 (1933). (4) hlair and Schicktanz, J . Research Xutl. Bur. Stand-
14600
I45M
ards, 17, 912 (1936); 20, 83 (1938).
(5) / 4400
Morton, “Laboratory Technique
in Organic Chemistry,” New York, McGraw-Hill Book Co., 1938.
RECEIVED July 25, 1938. Presented before the Division
FIGITRE 5
on differences in K. values and in structure as a supplementary method to fractional distillation, is apparent.
of Organic Chemistry at the 95th Meeting of the American Chemical Society, Dallas, Texas, April 18 t o 21, 1938. This paper represents portions of theses presented by W. A . Quebedeaux in partial fulfillment of the requirements for the degree of master of arts, and by H. G . Schutze in partial fulfillment of the requirements for the degree of doctor of philosophy at The University of Texas.
Preparation of Hydriodic Acid Suitable for Alkoxy1 and Friedrich-Kjeldahl Nitrogen Determinations E. P. CL4RK, Bureau of Entomology and Plant Quarantine, U. S. Department of Agriculture, Washington, D. C.
C
OMMERCIALLY available hydriodic acid has been used in the many volumetric methoxyl determinations made in this laboratory during the past few years (1). These acids invariably gave high blank values, which were materially reduced by a special purification procedure. However, instead of purifying a commercial acid, i t has been found more economical and as convenient to prepare a n acid for the purpose. The product obtained by the procedure given below is satisfactory, as i t is almost, if not entirely, free from blank and is stable for a long time. The same considerations also apply to hydriodic acid used in the Friedrich-Kjeldahl nitrogen determinations (a), in that the blanks on the specially prepared acids have been found to be from four to eight times lower than those of any commercial acids employed. The preparation of the acid for the purposes under discussion involves the well-known reduction of iodine with hypophosphorous acid and the scrubbing of the resulting constantboiling liquid with carbon dioxide. For this purpose 254 grams of iodine and 185 grams of Tyater were heated to about 50” C. in a 500-cc. flask with a groundjoint condenser, and 66 grams of 50 per cent hypophosphorous acid were added portionwise a t such a rate that the mixture boiled continuously until the iodine was reduced. Heat was then a p plied to the flask and the boiling was continued for 3 hours, during which time a stream of carbon dioxide was passed through t h e
solution. The position of the reflux condenser tvas then changed to allow distillation, and the constant-boiling hydriodic acid was collected. The yield was 447 grams. The preparation was stored in dark bottles and preserved by the addition of a little 50 per cent solution of hypophosphorous acid (about 1 cc. per pound).
A preparation made from one lot of “pure chemicals” of a reputable brand gave a zero alkoxyl blank and a blank of 0.02 cc. of 0.01 N acid for the Friedrich-Kjeldahl nitrogen method. Another preparation made from a different lot of similar chemicals gal-e a n alkoxyl blank of 0.01 cc. of 0.05 N thiosulfate. Hydriodic acid prepared in this manner from commercial hypophosphorous acid or hypophosphites cannot be used in the Zeisel method, as apparently they all contain sulfates. These are reduced with the formation of hydrogen sulfide, which naturally interferes by forming silver sulfide. If, however, sulfur-free hypophosphorous acid or hypophosphites were prepared for the purpose, the product would be satisfactory.
Literature Cited (1) Clark, E. P., J . Assoc. Oj’icial Agr. Chem., 15, 136 (1932) (2) Friedrich, A., Z. Physiol. Chem., 216, 68 (1933).
RECEIVED September 15, 1938.
