Kinetics of the reactions of methyl-2,3-dibromo-3- [4-substituted phenyl] propanoates with piperidine IV

ABSTRACT

The rates of elimination of a series of erythromethyl- 2,3-dibromo-3-[4-substituted phenyl] propanoates [1 alpha-d] have been determined conductimetrically in methanol using piperidine as a base. The elimination reactions gave exclusively Z-methyl-2-bromo-3- [4-substituted phenyl] propanoates [2 alpha-d]. The specific rate constants of the reactions gave a good Hammett correlation with p values of 0.39-1.31 which suggest a carbonionic transition state. The results suggested that the reaction proceeds by initial isomerization of the erythro-dibromo-compound to the threo-isomer, which spontaneously eliminates HBr to give [2 alpha-d]