Reactivity of N-alkyl derivatives of hydroxylamine in decomposition of 4-nitrophenyl diethylphosphonate in water and in cetyltrimethylammonium bromide micelles

Abstract

Neutral forms of hydroxylamine, N-methylhydroxylamine, and N,N-dimethylhydroxylamine are typical a-nucleophiles in water. In comparison with aryl anions of similar basicity their rate of reaction in the decomposition of 4-nitrophenyl diethylphosphonate is increased by about 10 2 times. Decomposition of the substrate is accelerated in cetyltrimethylammonium bromide micelles (about 4 to 30 fold). Hydroxylamine and its N-alkyl derivatives are the most effective low basicity nucleophiles. The sole factor responsible for the micellar effects is the concentration of the reagent in the surfactant micelles.Hydroxylamine (HA) is a unique a-nucleophile: its neutral and anionic forms are particularly effective decomposers of acyl compounds as substrates, including extremely toxic phosphate esters, over a wide range of acidic media (pH ³ 6.0) [1-4]. In particular, the anion of hydroxylamine is the "leader" among a-nucleophiles in nucleophilic substitution reactions with electron-poor centers -carbon, phosphorus, sulfur -and its reactivity is close to the limit for a-nucleophiles. N-Alkylhydroxylamines -N-methyl-and N,N-dimethylhydroxylamines (N-MeHA and N,N-(Me) 2 HA) are also typical a-nucleophiles. In fact, in reactions with an activated ester -bis(2,4-dinitrophenyl) phosphate -HA, N-MeHA, and N,N-(Me) 2 HA have anomalously high reactivity (³10 times faster than O-methylhydroxylamine) [1,2]. Nevertheless, it is not evident that the a-effect and the order of change in nucleophilicity of HA and its N-alkyl derivatives would remain the same with less reactive substrates. With the objective of constructing a system for the destruction of ecotoxicants it is necessary to take into account a whole range of factors, including solubility in water. One method for increasing the solubilization of organophosphorus compounds (OPC) is to carry out reactions in aqueous solutions of surface-active substances. The correct choice of surfactant -cationic, neutral, or anionic -for decomposition of OPC should lead to an increase in the observed rate of reaction.In the present work the reactivity of neutral forms N-methylhydroxylamine and N,N-dimethylhydroxylamine in water and hydroxylamine, N-methylhydroxylamine, and N,N-dimethylhydroxylamine in the presence of a cationic surfactant -0040-5760/07/4304-0247