Alkali-Metal Ion Catalysis and Inhibition in Nucleophilic Displacement Reaction of O-Ethyl O-4-Nitrophenyl Phenylphosphonothioate with Alkali-Metal Ethoxides

作者：Um Ik Hwan^*; Kang Ji Sun; Shin Minah

来源：Bulletin of the Chemical Society of Japan, 2013, 86(6): 736-741.

DOI：10.1246/bcsj.20130015

A kinetic study on nucleophilic displacement reactions of O-ethyl O-4-nitrophenyl phenylphosphonothioate (an insecticide called EPN) with alkali-metal ethoxides (EtOM; M = Li, Na, K, and K/18-crown-6-ether) is reported. Dissection of pseudo-first-order rate constant (k(obsd)) into the second-order rate constants for the reaction of EPN with the dissociated EtO- (k(EtO)-) and ion-paired EtOM (k(EtOM)) has revealed that the reactivity increases in the order k(EtOLi) %26lt; k(EtO)- %26lt; k(EtONa) %26lt; k(EtOK) %26lt; k(EtOK/18-crown-6-ether), indicating that Li+ inhibits the reaction while the other M+ ions behave as a Lewis acid catalyst in the order Na+ %26lt; K+ %26lt; 18C6-complexed K+. The contrasting M+ ion effects have been explained in terms of the hard and soft acids and bases (HSAB) principle, since EPN, as a polarizable P=S centered electrophile, would exert a weak interaction with Li+ (a hard acid) but a strong interaction with the 18C6-complexed K+ ion (a soft acid). M+ ions catalyze the current reaction by increasing the electrophilicity of the reaction center. EPN is less reactive than O-4-nitrophenyl diphenylphosphinothioate but is more reactive than O-4-nitrophenyl O,O-diethyl thiophosphate. Factors governing the reactivity of these P=S centered electrophiles are discussed.

• 出版日期2013-6-15