Metal ion mediated hydrolysis of 4-nitrophenylphosphate in microemulsion media: catalytic versus stoichiometric effects

Abstract

The hydrolysis of 4-Nitrophenylphosphate (NPP) as model substrate in the presence of several cobalt (III) amine [N4Co(OH)(H2O)]2+ and copper bipyridyl [Cu(bpy)(H2O)2]2+ complexes in oil in water microemulsion media was investigated. The reaction was monitored by measuring the absorbance of the nitrophenolate ion produced in the reaction aliquots with time under the experimental conditions. The order of effectiveness of the microemulsion systems towards the hydrolysis of NPP in the presence of these metal ions were found to be cationic > anionic > aqueous at neutral pH. The results of the present investigation exhibits stoichiometric turnovers for the 1:1, 2:1 and 3:1 cobalt to NPP ratio and catalytic turnovers for the [Cu(bpy)2+ to NPP ratio of 1:20. Catalysis in the microemulsion mediated reaction solutions was evident even in low concentrations of the metal ions in 1:2000 metal to NPP ratio. An explanation for the enhanced catalytic activity of the [Cu(bpy)(OH)(H2O)]2+ complex for the hydrolysis of NPP is afforded and the application of the above model systems for possible environmental decontamination of toxic organophosphates is anticipated.