Kinetics of base‐catalysed ring closure of methyl 2,6‐dinitrophenylsulfanylethanoate

Abstract

AbstractThe base‐catalysed ring closure of methyl 2,6‐dinitrophenylsulfanylethanoate gives 2‐methoxycarbonyl‐7‐nitrobenzo[d]thiazole‐3‐oxide. The kinetics of this ring closure were studied by means of UV–visible spectrophotometry in methanolic buffers of N‐methylmorpholine–N‐methylmorpholinium chloride and N‐methylpiperidine–N‐methylpiperidinium chloride at 25°C at ionic strength I = 0.1 mol l−1. The dependences of kobs on the base concentration are not linear, their slopes decreasing with increasing base concentration at constant ratio of the buffer components. The reaction mechanism was suggested on the basis of comparison with the ring closure kinetics of methyl 2,4,6‐trinitrophenylsulfanylethanoate. The rate‐limiting step of the reaction sequence consists in formation of the conjugated base of substrate 1. Copyright © 2005 John Wiley & Sons, Ltd.