Theoretical Studies on the Mechanism of Pyridinolysis of Y-Substituted Phenoxy Hydrogen Isothiocyanophosphonate

초록

The kinetics and mechanism of the pyridinolysis (XC5H4N) of phenoxy hydrogen isothiocyanophosphonate (Y-C6H4O(P=O)(H)NCS) in acetonitrile are investigated at room temperature 25.0 ℃. The Hammett and Brønsted correlations, physical and thermodynamic parameters as well as molecular orbital overlapping indicate the nucleophilic attack and leaving group (-NCS) departure strategies. These are interpreted to indicate a mechanistic behavior for the reactions whether these are following concerted or a stepwise route during expulsion of the isothiocyanate (NCS) leaving group from the intermediate or TS. The positive and negative ρX, and βX values imply the characteristics of the nucleophilic attack. In addition the steric effects of the ligands play an important role in determining the pyridinolysis rates of isothiocyano phosphonates.