A SOLID ADDITICN COMPOUND OF ACETIC ACID AKD STANKIC CHLORIDE BY ARTHUR W. DAITDSON
In 1 9 z j , Stranathan and Strong,' in an investigation of the viscosities, electrical conductivities and specific volumes of acetic acid-stannic chloride solutions, concluded that the extremely high viscosity of some of the solutions and the remarkable deviation of this and other properties from an additive relationship, were to be attributed to the presence in the solution of a compound of the two components, which they suggested might have the composition SnCl4.3CH3COOH. An attempt to determine the freezingpoint curve of the system was reported as unsuccessful because of the tremendous degree of supercooling encountered in the very viscous mixtures. Immediately after the appearance of the article referred to, the present writer, being interested in the subject of addition-compound formation in acetic acid solution, prepared about I O C.C. of a mixture of anhydrous stannic chloride and 99.770 glacial acetic acid in the proportions of one mol of the former substance to three of the latter, and attempted to isolate a solid addition compound by maintaining the solution at -33' in a bath of liquid ammonia for several hours. No crystallization occurred, however, and the test-tube containing the mixture was stoppered and allowed to stand at room temperature; further examination a t intervals showed no change, and the tube was set aside. Recent inspection, after the mixture had stood for over two years altogether, and had not been examined or disturbed for some months. revealed the presence in the bottom of the tube of about 0.5 C.C.of solid, in the form of a compact mass of transparent colorless crystals. Vigorous shaking of the mixture produced no further crystallization, indicating that the solid was probably not of the same composition as the solution. The crystals were separated from the solution by filtration, and were dried by pressing them between porous tiles, with as little exposure to the atmoaphere as possible. In this manner there was obtained about 0.35 gram of a white crystalline powder. This substance was apparently stable in a desiccator, but deliquesced very rapidly in the moist air of the laboratory. It had a decided odor of acetic acid, and dissolved readily in water to give a markedly acid solution, clear a t first but gradually acquiring a white turbidity on standing. Qualitative tests showed the presence of stannic and of chloride ions in the solution. These facts left little room for doubt that the substance was an addition compound of stannic chloride and acetic acid. The amount of substance remaining after these preliminary tests being just about sufficient for a single analysis, a determination of its chlorine con-
* Stranathan and
Strong: J. Phys. Chern., 31, 1420 (1927).
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tent was made. After the tin had been precipitated with hydrogen sulfide, the stannic sulfide filtered off, and the very dilute solution boiled until excess hydrogen sulfide was expelled, the chlorine was precipitated as silver chloride in the usual manner. The result of the analysis was as follows. Subs., 0.1900 : AgCl, 0.2126. Calcd. for . 27.68%. SnC14.4CH3COOH : C1, ~ 8 . 3 3 7 ~Found: While it is to be regretted that the amount of substance available did not permit of a check upon this analysis, it is believed that the evidence presented is sufficient to establish the existence of a solid addition compound of the formula SnC14.4CH3COOH. This, of course, does not preclude the possibility of the presence of other compounds in the solution also. It should be mentioned here that Fichter and Herszbeinl have recently reported the preparation of a stannic dichloride diacetate, SnClZ(CH3COO),, made by adding stannic chloride t,o an equal quantity of acetic acid containing some acetic anhydride, and distilling off part of the mixture.2 They suppose that the first step in the reaction is the formation of the addition compound, SnCl4.2CH3COOH, which loses hydrogen chloride to give the compound finally obtained; this hypothesis was not verified, however. I n view of the decidedly unusual properties of the system under discussion, a study of its properties from the point of view of the phase rule would be of great interest. It appears from the facts here noted, however, that the extreme slowness wit'h which equilibrium between solid and liquid phases is attained in these mixtures, would offer an almost unsurmountable obstacle to such an investigation. Summary :-The occurrence of compound formation in solutions of acetic acid and stannic chloride, suspected by several previous authors, has been verified by the isolation from such a solution of a solid addition compound, apparently having the formula SnClr.4CH3COOH. Chemical Laboratory, University of Kansas, Lawrence. Kansas.
' Fichter and Herszbein: Helv. Chim. Acta, 11, 431 (1928). This compound also is described as a white, crystalline, deliquescent solid; unlike the addition compound reported in the present note, however, it is said to fume in the air. The chlorine content calculated for stannic dichloride diacetate is 23.05%. 2
