March, 1959
ISOTOPIC EXCHANGE REACTIONS IN LIQUIDSULFUR DIOXIDE
volve the dissociation of a chloride ion from a PC1-bond. These bonds are however strengthened by the formation of either an oxygen or a chloride bridge. I n reactions 2 and 7 a chloride ion is dissociated from Sb. Both reactions are not extremely likely with a somewhat higher mobability for reaction 2, since the P-0-Sb b k d will be sGonger than the P-C1-Sb bond. I n reaction 4 the P-0 bond is to be broken, which is stronger than the Sb-0 bond, that would remain according to reaction 4. I n addition dissociation of a 2-2 valent electrolyte in a solvent of low dielectric constant would only be possible with a higher solvation tendency, than is actually observed in Reaction 6 is, however, easily possible. In the P-ClSb bridge the P-C1 bond may be weaker than the C1-Sb bond, as shown by the fact that SbC&is a stronger acid than POcl3 or PCl6. The electrostatic contribution of the bond will allow the dissociation t o P0Cl2+ and SbC1,- ions as univalent electrolytes of similar ionic size are dissociated in phosphorus oxychloride. This reaction will be favored by the solvation of the POClz+-ion Poclp’ f P O c h
[Poc13~Poc1~] +
The potentiometric measurements show that the chloride ion activity in the SbCh solution is very small as compared with that of the pure solvent. Therefore reaction 2, which would lead t o an in-
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crease in chloride ion activity cannot be of any importance. Thus the order of the probabilities of the reactions leading to the formation of ions will be as follows: 6 >> 2 > 7 > 4 and 6 7 >> 2 4. The reactions following reaction 5 are therefore more likely than the reactions following reaction 1. It is very likely that due to solvation processes reaction 6 is more probable than 5 so that the actual competition in solution will occur between reaction 6 and 1 (since 2 3 4
