| Abstract
| - A kinetic study is reported for aminolysis of aryl diphenylphosphinothioates (2a−i). The phosphinothioates2a−i are less reactive than aryl diphenylphosphinates (1a−i), the oxygen analogues of 2a−i, regardlessof the basicity of the leaving aryloxides or the attacking amines. The Yukawa−Tsuno plot for the reactionsof 2b−i with piperidine exhibits good linearity with a small r value (r = 0.28), indicating that the leavinggroup departs at the rate-determining step with a small degree of bond fission. Reactions of2,4-dinitrophenyl diphenylphosphinothioate (2a) with alicyclic secondary amines result in a good linearBrønsted-type plot with βnuc = 0.52, implying that the reactions proceed through a concerted mechanism.The βnuc value determined for the reactions of 2a is slightly larger than that reported for the correspondingreactions of 2,4-dinitrophenyl diphenylphosphinate (1a, i.e., βnuc = 0.38), suggesting that reactions of 2aproceed through a tighter transition state (TS) than that of 1a. The reaction of 2a with piperidine exhibitsa ca. 0.4 kcal/mol more favorable enthalpy of activation (ΔH⧧) than that of 1a. On the contrary, theentropy of activation at 25.0 °C (TΔS⧧) is ca. 1.5 kcal/mol more unfavorable for the reaction of 2a thanfor that of 1a. This result supports the proposal that the reaction of 2a proceeds through a tighter TS thanthat of 1a and explains why 2a−i are less reactive than 1a−i.
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