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.