Microgels with Trialkylmmoio Side-Chains Function as CAtalysts for the Alkaline-Hydrolysis of Substituted Phenyl Luarte Esters

Microgels incorporating 2-(tetradecyldimethylammonio)ethyl methacrylate bromide have been prepared by emulsion polymerisation with methyl methacrylate, 2-ethoxyethyl methacrylate and ethylene glycol dimethacrylate in the molar ratio 0.15:0.45:0.30:0.10 respectively. The microgel solubilises aryl laurate esters in aqueous solution and catalyses the alkaline hydrolysis of these esters; the variation of rate constant with microgel concentration indicates a complexation phenomenon with the 4-nitrophenyl ester. The reactivity of the microgel sol with the laurate esters is similar to that of the analogous micellar system from cetyltrimethylammonium bromide (CTAB) described by Al-Awadi and Williams (J. Org. Chem., 55 (1990) 2001). The rate constant for the microgel-catalysed reaction of hydroxide ion with the substituted phenyl laurate esters obeys the Bronsted correlation: logk(OH)(cat)=-0.53pK(a)+4.49 The value of the Bronsted beta(lg) (-0.53) is similar to that observed for CTAB-catalysis and for uncatalysed alkaline hydrolysis; it indicates that the catalytic site of ester hydrolysis resides in an aqueous-like region of the microgel.