Nucleophilic Substitution Reactions of O-Methyl N,N-Diisopropylamino Phosphonochloridothioate with Anilines and Pyridines

Abstract

The kinetic studies on the reactions of O-methyl N,N-diisopropylamino phosphonochloridothioate with Xanilines and X-pyridines have been carried out in acetonitrile. The free energy relationship with X in the anilines exhibits biphasic concave upwards with a break region between X = (H and 4-F), giving unusual negative β X and positive ρ X values with weakly basic anilines. The unusual phenomenon is rationalized by isokinetic relationship. A stepwise mechanism with a rate-limiting leaving group departure from the intermediate is proposed based on the selectivity parameter and variation trend of the deuterium kinetic isotope effects with X. The free energy relationship with X in the pyridines exhibits biphasic concave upwards with a break point at X = 3-MeO. A concerted mechanism is proposed based on relatively small β X value, and frontside and backside nucleophilic attack are proposed with strongly and weakly basic pyridines, respectively.