Comparative Studies on Prussian Blue or Diaquatetraaminecobalt(III) Promoted Hydrolysis of 4-Nitrophenylphosphate in Microemulsions

Comparative reactivities of three diaqua(tetraamine)Co(III) complexes towards hydrolysis of 4-nitrophenyl phosphate was undertaken. The results were contrasted with prussian blue promoted hydrolysis of 4-nitrophenyl phosphate. The tetraamineCobalt(III) complexes accelerated the hydrolytic reaction to varying degrees with the following reactivity order. [(tn)2Co(OH2)2]3+ < [(trpn)Co(OH2)2]3+ < [(tme)2Co(OH2)2]3+ [ tn = trimethylenediamine; tme = 1,1,2,2-tetramethyl-1,2-diaminoethane; trpn = tris(3- aminopropyl)amine].These observations are attributed to the active aquo-hydroxo forms of the tetraamineCobalt(III) complexes. The hydrolysis rate for prussian blue promoted hydrolysis was comparable to that obtained for [(tme)2Co(OH2)2]3+. The mixed valence bimetallic centers of prussian blue aid in substrate binding and organizing the nitrophenyl phosphate for effective intramolecular nucleophilic attack by coordinated hydroxide or water.