Multiparameter kinetic analysis of alkaline hydrolysis of a series of aryl diphenylphosphinothioates: models for P=S neurotoxins

摘要: Alkaline hydrolysis of a series X-substituted-phenyl diphenylphosphinothioates (2a-i) in 80 mol%/20 mol% DMSO at 25.0 ± 0.1°C has been studied kinetically and assessed through multiparameter approach. Substrates 2a to 2i are approximately 12 22 times less reactive than their P=O analogues 1a 1i (ie, the thio effect). The Bronsted-type plot for reactions is linear with βlg = −0.43, consistent concerted mechanism. Hammett plots correlated σo σ− constants also support mechanism; Yukawa-Tsuno results an excellent correlation ρX = 1.26 r = 0.30, indicating that expulsion leaving group occurs rate-determining step (RDS). ΔH‡ value increases from 10.5 11.7 13.9 kcal/mol as substituent X changes 3,4-(NO2)2 4-NO2 H, turn, while TΔS‡ remains constant −6.0 kcal/mol. strong dependence on electronic nature indicates departs RDS. reaction mechanism origin effect discussed by comparison current kinetic those reported 1i. suggest useful OP neurotoxins abiotic (with varying degrees asynchronicity) when substrate bears good groups.