Methanolysis of pNPOAc under moderately alkaline conditions is catalysed by the alkaline- earth metal ion (Ca, Sr, Ba) complexes of 2-(mercaptomethyl)-18-crown-6 according to biphasic kinetics in which an initial burst of pNPOH release is followed by a zeroth-order phase. Two competing catalytic mechanisms contribute to the overall process,(i) a double displacement mechanism in which the complexed metal ion enables the SH group of the ...
