MICELLAR CATALYSIS OF ORGANIC-REACTIONS .37. A COMPARISON OF THE CATALYSIS OF ESTER AND AMIDE HYDROLYSIS BY COPPER-CONTAINING MICELLES

The hydrolysis of a number of nitroactivated esters and amides has bee n studied in the presence of copper-containing metallomicelles at neut ral pH. The relative rates of hydrolysis in the pure metallomicelle an d in co-micelles with either cetyltrimethylammonium bromide (ctab) or Triton X-100 depends on the hydrophobicity of the substrate and whethe r it is completely solubilized by the copper micelle. Thus it depends on the concentration of the copper micelle. At low concentrations of c opper micelle (0.2 mM) where the substrate is incompletely solubilized , the reaction is faster when 2 mM ctab is added. At higher concentrat ions (>0.6 mM) where the substrate may be almost completely solubilize d by the copper micelle, the reaction is slower when 2 mM ctab is adde d. For ester hydrolysis the presence of either a carboxylic acid group or a heterocyclic nitrogen atom close to the reaction centre resulted in much larger catalysis by the metallomicelle than for model compoun ds without these additional groups. It is postulated that these groups coordinate with the metal ion and thus present the reaction centre cl ose to a metal-bound hydroxyl resulting in a significant increase in t he rate of bond formation, which is the rate-determining step for este r hydrolysis. For amide hydrolysis the presence of a carboxyl group or tho to the reaction centre did not lead to larger catalysis by the cop per micelle than for the compound without this group. This difference is attributed to the different rate-determining steps for amide and fo r eater hydrolysis.