KINETICS OF REACTIONS OF AMINES WITH ALPHA-NITRO-BETA-SUBSTITUTED-STILBENES IN 50-PERCENT ME2SO-50-PERCENT WATER - SEARCH FOR THE INTERMEDIATE IN NUCLEOPHILIC VINYLIC SUBSTITUTION-REACTIONS

The kinetics of the reaction of Ph(OMe)C=CPh(NO2) with piperidine, morpholine, pyrrolidine, and rc-butylamine, and of the reactions of piperidine with Ph(Cl)C=CPh(NO2), Ph(I)C>=CPh(NO2), and Ph(SEt)C=CPh(NO2) where measured in 50% Me2SO-50% water at 20 °C. The reactions are discussed within the framework of the multistep mechanism of nucleophilic vinylic substitutions with amines. Nucleophilic attack is rate limiting in the reactions of piperidine with Ph(LG)C=CPh(NO2) when LG = Cl, I, EtS, and in the reactions of Ph-(OMe)C=CPh(NO2) with all the amines at high pH. At low pH, methoxide departure becomes partially rate limiting in the reactions with piperidine, morpholine, and pyrrolidine. The intermediate Ph(OMe)(NRRO-CCPh(NO2)- could not be directly observed. The failure to detect the intermediate is not caused by a thermodynamic stability of the intermediate with respect to reactants that is too low, but by a rate of conversion to products that is too fast compared to its rate of formation. © 1990, American Chemical Society. All rights reserved.