The acid-catalyzed hydrolysis of phosphinates. IV. Pentacoordinate intermediate formation during hydrolysis of a phosphinothionate

Abstract

The hydrolysis of methyl dimethylphosphinothionate in D2SO4–D2O solution gives as products the phosphinic acid and methyl dimethylphosphinate. The bell-shaped pH–rate profiles for both reactions as well as the values of Bunnett's w and w* (3.31 and −0.21 respectively), Bunnett–Olscn's [Formula: see text] (0.82), and Yates–McClelland's r (6.56) support an A-2 pathway. The results are interpreted in terms of the presence of a common pentacoordinate intermediate along the reaction pathway. The pKa of the above ester as well as that of methyl dimethylphosphinodithioate are reported (−5.53 and −5.38 respectively).