Retentive solvolysis. Part X. Retentive solvolysis of optically active para-substituted 1-phenylethyl p-nitrobenzoates in phenolic solvents: rate, steric course, product distribution, and mechanism

Abstract

The title compounds (Ia)–(IIIa) were subjected to solvolysis in the presence of sodium phenoxide in pure phenol or in phenol-benzene (1 : 1 w/w) as solvent. Both polarimetric and titrimetric rate constants (K_p and K_t) decrease in the order (Ia) > (IIa) > (IIIa); K_p values for (Ia) and (IIa) exceed those for K_t over the whole range of concentration of added sodium phenoxide, whereas K_p and K_t for (IIIa) coincide with each other. The major products, the phenyl ethers (Ib)–(IIIb), show net retention of configuration; the extent of retention was 16.6% for (Ib) in phenol-benzene at 25°, 34.5% for (IIb), and 90.0% for (IIIb) in phenol at 125°, respectively. The C-alkylated products, o- and p-1-phenylethylphenols, are formed to a small extent only and undergo net inversion with predominant racemization in the phenolysis of (IIa). Variations in the yield and in the extent of retention for (Ib)–(IIIb) have been examined for various concentrations of added sodium phenoxide; variations in the optical rotation of recovered substrate and those in the extent of retention of the phenyl ether have also been determined in the course of each phenolysis. On the basis of this evidence, the mechanisms and steric courses of these reactions are discussed. Maximum rotations of the phenyl ethers (Ib)–(IIIb) and 1-arylethanols (Ic)–(IIIc) have been determined by chemical or n.m.r. shift reagent methods; the absolute configurations of (IIIb) and (IIIc) have also been assigned by the use of a chemical method.