METALLOMICELLES AS CATALYSTS OF THE HYDROLYSIS OF CARBOXYLIC AND PHOSPHORIC-ACID ESTERS

Lipophilic ligands 2-4 have been synthesized. In the presence of Cu(II) ions, they form metallomicelles that are catalytically active in the cleavage of the p-nitrophenyl esters of acetic, hexanoic, and dodecanoic acids. Catalysis was also observed in the cleavage of p-nitrophenyl diphenyl phosphate. The apparent pK(a) of the Cu(II)-coordinated hydroxyl of ligand 2a, in the micellar aggregate, is 7.7, as estimated from the rate vs pH profiles for both classes of esters: this suggests that the hydroxyl is involved as a nucleophile in the hydrolytic cleavage, which proved to be really catalytic process. The ligand bearing the free hydroxyl (2a) is more effective in the cleavage of carboxylate esters than ligands with the methylated alcoholic group (2b) or devoid of it (4); the opposite behavior is observed in the cleavage of the phosphate triester. A rationale is offered that calls for the difference in the coordination ability to the metal center of phosphate and carboxylate esters.