Comparative studies on prussian blue or diaquatetraamine-cobalt(III) promoted hydrolysis of 4-nitrophenylphosphate in microemulsions

Abstract

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(OH) 2) 2] 3+ < [(trpn)Co(OH) 2) 2] 3+ < [(tme) 2Co(OH) 2) 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(OH) 2) 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.