Combined dual substituent constant and activation parameter analysis assigns a concerted mechanism to alkaline ethanolysis at phosphorus of Y-substituted phenyl diphenylphosphinates

摘要: Second-order rate constants have been measured for reactions of Y-substituted phenyl diphenylphosphinates (1a–h) with EtO−K+ in anhydrous ethanol. A linear Bronsted-type plot is obtained βLg = −0.54, a typical value which proceed through concerted mechanism. The Hammett plots correlated σo and σ− are but exhibit many scattered points, while the corresponding Yukawa–Tsuno results excellent correlation r 0.41. 0.41 indicates that leaving group departs at rate-determining step (RDS) whether either or stepwise However, mechanism departure occurs RDS excluded since incoming EtO− ion much more basic poorer than aryloxide. ΔH‡ values determined current strongly dependent on nature substituent Y, ΔS‡ remain constant changing Y group, i.e., from H to 4-NO2 3,4-(NO2)2. These trends also support