Synthesis, kinetic study, and reaction mechanism: nucleophilic substitution reactions of butyl methyl chlorophosphate with substituted anilines and deuterated substituted anilines in acetonitrile

Authors : Hasi Rani Barai, Md. Mahbubur Rahman, Sang Woo Joo

Pages : 501-510

View : 15 | Download : 12

Publication Date : 9999-12-31

Article Type : Makaleler

Abstract :This study demonstrated the kinetics of nucleophilic substitution reactions of butyl methyl chlorophosphate (2) with X-anilines (XC$_{6}$H$_{4}$NH$_{2})$ and deuterated X-anilines (XC$_{6}$H$_{4}$ND$_{2})$ in MeCN at 55.0 \textpm\ 0.1 \textdegree C together with the general optimized method for the synthesis of 2 under mild conditions. Different spectroscopic characterizations revealed the formation of 2 with high purity. The free energy relationship with the substituents X in the anilines exhibited biphasic concavity upwards with a break point at X $=$ H, which induced large negative $\rho_{X}$ and small positive $\beta_{X}$ values. The deuterium kinetic isotope effects (DKIEs) were secondary inverse ($k_{H}$/$k_{D}$ \textless\ 1: 0.702--0.918) and the magnitudes were increased with the change of nucleophiles from weakly basic to strongly basic anilines. A concerted mechanism with a rate-limiting leaving group departing from the intermediate is proposed based on the selectivity parameters and the variation of DKIEs with X.
Keywords : Phosphoryl transfer reaction, concerted mechanism, butyl methyl chlorophosphate, Hammett and Br{o}nsted constants, deuterium kinetic isotope effects