Retentive Solvolysis. 15. Salt Effect ion the Retentive Phenolyses of 1-(p-Substituted phenyl)ethyl p-Nitrobenzoates. The Pattern of Salt Effect and the Number of Ion-Pair Intermediates in the SN1 Solvolysis

Article abstract of DOI:10.1246/bcsj.61.2917

The salt effect of sodium phenoxide on the polarimetric (k_p) and titrimetric rate constants (k_t) has exhibited pattern B for the phenolysis of optically active 1-(p-methylphenyl)ethyl p-nitrobenzoate (ROPNB; (1)) in pure phenol.The other patterns A, C, and D were previously observed for the phenolyses of 1-phenylethyl p-nitrobenzoates with p-MeO- (2), p-H- (3), and p-NO2-substituents (4), respectively.Thus, the k_p-k_t pattern changes in the order A -> B -> C -> D as the stability of the intermediate decreases in the order of 2 > 1 > 3 > 4.All the k_p-k_t patterns can be correlated with the ion-pair stage for product formation, i.e., the pattern A with the second ion-pair intermediate and the patterns B, C, and D with the first one.The pattern of salt effect on the product distribution (percent of ROPh, o- and p-RC6H4OH, and p-MeC6H4CH=CH2) for 1 is also compatible with the k_p-k_t pattern B.