Kinetics and Mechanism of the Aminolysis of 4-Nitrophenyl Dithioacetate

Article abstract of DOI:10.1021/jo00052a010

The reaction of the title substrate with a series of secondary alicyclic amines has been the subject of a kinetic study in aqueous solution, 25 deg C, ionic strength 0.2 M (KCl).With the amine in excess, pseudo-first-order rate constants (k(obsd)) are observed.The order in amine varies from 1 to 2 depending on the basicity of the amine and reaction conditions.A reaction scheme is deduced on the basis of the existence of zwitterionic (T(+/-)) and anionic (T(-)) tetrahedral intermediates.Proton transfer from T(+/-) to an amine or base (to yield T(-)) seems to compete with 4-nitrothiophenoxide (NPS(-)) expulsion from T(+/-).The pKa of T(+/-) and all the rate microconstants of the scheme are estimated.The rates of expulsion of NPS(-) and amine from T(+/-) are smaller than those from analogous T(+/-) formed in the aminolyses of O-ethyl S-(4-nitrophenyl)dithiocarbonate and 4-nitrophenyl thiolacetate.It is claimed that substitution of Me by RO (R = alkyl) or S(-) by O(-) in T(+/-) destablizes this intermediate.