Acceptor properties of metal halides. Part V. Stannic chloride as a catalyst for the racemisation of α-methylbenzyl chloride in benzene solution, and the effect of hydrogen chloride on the catalysed reaction
Abstract
The racemisation of α-methylbenzyl chloride (RCl) in benzene is catalysed by stannic chloride. In the temperature range 6–35°, the racemisation probably results from the formation of ion pairs of formula [R+ SnCl5–]. The ΔH‡ and ΔS‡ values for this process are 8·5 kcal. mole–1 and –30 e.u. respectively. Hydrogen chloride alone does not provide detectable catalysis. Present together with stannic chloride it leads, by solvating the transition state for ion-pair formation, to a small enhancement of the stannic chloride catalysis. Our results for this system are not in agreement with those of Böhme and his co-workers.