Kinetic Studies of Solvolysis. XI. The Steric Course of the Phenolyses of Optically Active α-Phenylethyl Chloride in Mixtures of Various Phenols and Organic Solvents—A Mechanism for the SN1 Reaction with a Net Retention of Configuration

Abstract

Abstract The SN1 phenolyses of optically active α-phenylethyl chloride in binary mixtures of organic solvents and certain substituted phenols (i. e., phenol, p-cresol, p-chloro- and p-nitro-phenol) proceed in the presence of aniline and of triethylamine to give the corresponding α-phenylethyl substituted-phenyl ethers with a predominantly-retained configuration. In binary mixtures of benzene and various phenols, the extents of retention for the ethers are slightly reduced at the higher base concentrations. However, in binary solvents of acetonitrile and certain phenols, the optical purities of the ethers with retained configurations decrease continuously with the base concentrations, while at the higher concentrations (∼0.4 m) the steric courses change to the inverted course. The C-alkylated (α-phenylethylated) derivatives of these phenols, isolated along with the phenyl ethers, have inverted configurations, irrespective of the configurations of the corresponding phenyl ethers. These results are all consistent with a mechanism in which a molecule of the phenol reacts with the SN1 ion-pair intermediate of the phenolysis to give a phenyl ether with a retained configuration, probably by SNi-like four-center substitution, whereas the reaction of a phenoxide anion with the SN1 intermediate proceeds predominantly by the Walden inversion mechanism yielding a phenyl ether and α-phenylethylated phenols with inverted configurations.