JOURNAL OF T H E AMERICAN CHEMICAL S O C I E T Y (Registered in U. S. P a t e n t Office)
(9 Copyright, 1937, b y t h e American Chemical Society) NUMBER 21
JANUARY 5 , 1957
VOLUME78
PHYSICAL AND INORGANIC CHEMISTRY [ CONTRIBUTIOX FROM
THE
DEPARTMENT OF CHEMISTRY OF
THE
USIVERSITYOF \VrscoxsIv]
Isotopic Exchange between SnC1, and 2-Chlorobutane B Y REEDA. HOWALD AND
JOHN
E. WILL.4RD
RECEIVEDATGUST6, 1956 The homogeneous exchange of C136between SnC14 and 2-chlorobutane occurs a t a measurable rate in heptane solution a t I n heptane a t room temperature exchange was observed only in the presence of HC1 and of the white solid which is formed when water is added to SnC14. The data on the homogeneous exchange appear t o be most consistent with a mechanism involving formation of a rather stable (SnCl4.C4HyC1)complex.
140' and faster at 160'.
Introduction A number of isotopic exchange reactions between alkyl halides and Friedel-Crafts catalysts have been studied1+ because the interactions between these materials have played an important role in mechanisms postulated for Friec'el-Crafts reactions. Recent work in this Laboratory' has shown that negligible exchange of C136occurs between SnC14 and 2-chlorobutane in the vapor phase a t 200' in 180 minutes. The present paper presents the results of investigations of the same exchange in condensed systems where measurable reaction has been observed.'
Experimental Materials.-SnCl,, HCI and 2-chlorobutane were purified and dried as in the earlier work,' and radioactive SnC& was prepared by the exchange between HCl36 and liquid SnC14 as previously described.' Phillips Petroleum Co. pure grade normal heptane was passed through a silica gel column, greatly reducing the absorption of the solvent in the ultraviolet so t h a t the optical density in a one cm. cell was less than 0.1 a t wave lengths above 2200 A. This heptane was distilled through a P 2 0 5 (1) R. A. Howald a n d J. E . Willard, THIS J O U R K A L , 77, 2046 (1955). (2) C. H. Wallace a n d J. E. Willard, ibid., 72, 5275 (1'2.50). (3) M. Blau a n d J. E. Willard, ibid., 73, 442 (19.51), 75, 3330 (1953). (4) F. Fairbrother, J . Chem. Soc., 293 (1941). ( 5 ) N. E. Brezhneva, S . Z . Roginskii a n d A. I. Shilinskii, J . Phys. Chem. U S S R . , 1 0 , 368 (1937); Acta Physicochim.,C S S R . , 7 , 201 (1937). (6) G . B. Kistiakowsky a n d J . R. Van Wazer, THISJ O U R N A L 6S, 1829 (1943). (7) F u r t h e r details of these experiments m a y be found in t h e Ph.D. thesis of Reed A. Howald filed with t h e University of Wisconsin Library in 1955 and available from University Microfilms, Ann Arbor, Michigan.
glass wool column into the vacuum system used to fill the reaction cells. Phillips Petroleum Co. pure grade butene-2 was passed into the vacuum system through a P?Os-glass no01 column. Ethyl chloride, used as the solvent in some of the runs, was purified by bubbling through a column of concentrated H&04 and then passing through columns of KaOH pellets and PLOson glass wool. Filling and Analysis of Reaction Tubes.-All of the runs mere made in sealed Pyrex tubes filled on a vacuum system. In general the tubes had volumes of about 6 ml. and held 1-2 ml. of solution. SnC14 was metered out roughly by filling a known volume to the vapor pressure of SnC14 a t some temperature below t h a t of the room. More accurate values were obtained a t the end of each experiment by titrations with NaOH and A4gSOd. The amounts of 2chlorobutane were measured by pressure readings on a mercury manometer while the vapor was confined in a known volume. The volumes of solution were determined after the cells were broken open for analysis. After a reaction tube had been exposed a t the desired temperature for the desired time, it was broken open, water and heptane were added to give two phases each of 5 ml., and this two-phase system was shaken vigorously. During this procedure the heptane layer became very cloudy and then cleared up with the formation of white flakes of stannic hydroxide, most of which settled to the bottom of the water layer. The water and heptane solutions from each run were placed separately in the annular jackets of glass-walled solution-type Geiger-Muller tubes and their radioactivities were counted. An empirical correction was applied in comparing activities from different tubes and mith different solvents. Solid Formed by Traces of Water.--A distinct cloudiness appeared when SnCl4 was added to heptane in preparing the reaction tubes unless the SnCl, was dried by exposure to Pn0~in the vacuum system just before i t was added. On standing for about half a n hour the white solid responsible for the cloudiness settled out on the walls of the tube, leaving a clear solution. This behavior was a very sensitive test for small amounts of water and extreme care was necessary in degassing the walls of the vacuum system and in drying all the materials in order to obtain initially clear solutionq.
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REEDA. HOWALD AND JOHN E.
Most of the cells reported here showed a t least a trace of cloudiness; however even when the SnC14 was not freshly dried only small amounts of HzO were present, as shown by the fact t h a t the addition of 0.01 to 0.07 mole of H 2 0 per mole of SnCll gave considerably larger aniounts of white solid.
LVIILLARD
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