Structure–reactivity correlations in the aminolysis of aryl dithiomethyl- and dithiophenylacetates with anilines in acetonitrile

Abstract

The kinetics and mechanism of the anilinolysis (XC6H4NH2) of dithio esters, RC(S)SC6H4Z with R = C2H5 and C6H5CH2 are investigated in acetonitrile at 45.0 °C. By application of various structure–reactivity correlations, selectivity parameters ρX, βX, ρZ, βZ and ρXZ are determined. The reactions are predicted to proceed stepwise with rate-limiting expulsion of the ArS− group. The dithio ester with R = C2H5 exhibits the fastest rate and the largest positive ρXZ value; this is interpreted to result from the strongest electron donating ability of the ethyl group in the intermediate and a crowded tetrahedral intermediate and transition state in which the nucleophile (X) and leaving group (Z) are in close proximity due to the bulky C2H5 group. Much faster rates are observed for the thiocarbonyl (CS) rather than carbonyl (CO) esters in the stepwise nucleophilic substitution reactions, which may be ascribed to the lower π*CS and σ*C–LG levels than those of the corresponding antibonding levels in the carbonyl esters. The normal kinetic isotope effects, kH/kD > 1.0, involving deuterated anilines suggest concurrent proton transfer with the expulsion of the ArS− leaving group in a four-center hydrogen bonded transition state.