Phenolysis and competing methanolysis of optically active 1-phenylethyl chloride in sterically hindered 2,6-dialkylphenol solvents

Abstract

Phenolysis of optically active 1-phenylethyl chloride was carried out in 2,6-dimethyl-(I), 2,6-di-isopropyl-(II), 2,6-di-t-butyl-(III), or 2,6-di-t-butyl-4-methyl-phenol (IV) as solvent at 125°. Rates of S_N1 phenolysis decreased in the sequence (I) > (II) > (III) > (IV)(relative rates 511 :6·46 : 1·00 : 0·038). In solvents (I) and (II) the corresponding aryl ethers and p-1-phenylethylphenols were obtained; in solvents (III) and (IV) no aryl ether was obtained, whereas 4-(1-phenylethyl)-2,6-di-t-butylcyclohexadienone and its 4-methyl derivative were isolated. The aryl ethers showed net retention of configuration, whereas all C-alkylated products in solvents (I)–(IV) underwent net inversion. Phenolyses in solvents (I)–(IV) containing 0·5–5% methanol gave methyl 1-phenylethyl ether with net retention, whereas methanolysis in methanol–benzene afforded the methyl ether with net inversion. The results can be accounted for by shielding of the ion-pair S_N1 intermediate from the rear by solvent phenol.