Quantitative treatment of reaction rates in functional micelles and comicelles

Comicelles of dodecyl[2-(hydroximino)-2-phenylethyl]dimethylammonium bromide (5) or N-phenylmyristohydroxamic acid (6) with cetyltrimethylammonium bromide (CTABr) are good dephosphorylating agents toward p-nitrophenyldiphenyl phosphate (p-NPDPP) at high pH where 5 and 6 are deprotonated to oximate and hydroxamate ions, respectively. The phosphorylated oximate rapidly reacts with OH^-, but the phosphorylated hydroxamate can be trapped with p-nitrophenoxide ion. Comparison of the rate constants in the comicelles with those for reactions in water, with monomeric oximate or hydroxamate moieties formed by deprotonation of [2-(hydroximino)-2-phenylethyl]triethylammonium bromide or N-phenylpropiohydroxamic acid, shows that the second-order rate constants in the micellar pseudophase are very similar to those in water. A similar comparison of rate constants in micellar and aqueous pseudophases can be made at high pH by using micelles of N,N-dimethyl-N-(2-hydroxyethyl)hexadecylammonium bromide and monomeric choline for a variety of reactions. In this system the micellar reaction of p-NPDPP is slower than predicted, and the role of substrate hydrophobicity and reaction mechanism is discussed.