Retentive solvolysis. Part 14. The methanol-perturbed phenolysis of optically active 2,2-dimethyl-1-(p-methoxyphenyl)propyl p-nitrobenzoate. The mechanism and the structure of the second ion-pair intermediate

Abstract

The polarimetric and titrimetric rate constants have been measured for the solvolysis of optically active 2,2-dimethyl-1-(p-methoxyphenyl)propyl p-nitrobenzoate (ROPNB) in phenol–methanol (97:3 w/w). The salt effect of added (Buⁿ)₄NClO₄ indicates that all products are derived from the second ion-pair intermediate (Int-2), not from the first (Int-1), as for the phenolysis in pure phenol. Competitive solvolysis, i.e., methanol-perturbed phenolysis, produced partially inverted ROPh, o- and p-RC₆H₄OH, and partially retained ROMe, whereas phenolysis in pure phenol afforded partially retained ROPh and o- and p-RC₆H₄OH. This stereochemical outcome demonstrates that Int-2, the key intermediate of these phenolyses, has an ion-pair structure shielded by a phenol molecule from the rear-side. The absolute configurations and the maximum rotations of all products have been determined.