The kinetics of nucleophilic dephosphorylation of p-nitrophenyl diphenyl phosphate by hydroxamate ions (R'(C=O)N(RO-)) have been investigated in aqueous cationic micellar media at pH 9.12 and 27 degrees C. The pseudo-first-order rate constant-surfactant profiles show micelle-assisted bimolecular reactions involving interfacial ion exchange between bulk aqueous media and micellar pseudophase. N-Substituted hydroxamate ion shows higher reactivity over the unsubstituted hydroxamate ions in cationic micellar media. The kinetic data are discussed in terms of the pseudophase ion exchange model.
There is currently a great deal of interest in the chemistry of hydroxamic acids. In recent years we have been studying the synthesis, structure and nucleophilicities of hydroxamic acids. This paper reports a kinetic study of reactivity of some hydroxamic acids RC(O)·N(OH)R′; R=C6H5·CH=CH, R′=4-CH3·C6H4 [p-tolylcinnamo hydroxamic acid]; R=C6H5, R′=4-CH3·C6H4 [p-tolylbenzo hydroxamic acid]; R=C6H5, R′=2-CH3·C6H4 [o-tolylbenzo hydroxamic acid] in aqueous mineral acids (HCl, HClO4 and H2SO4). The rate data of hydrolysis reaction revealed that the reactivity/stability sequence of the compounds is generally p-TBHA>o-TBHA>p-TCHA. An excess acidity analysis reveals that the reaction proceeds by nucleophilic attack of water molecule on the protonated substrate.
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