A Review: General Base Catalysis Hydrolysis of Organophosphorus Insectisides by Different Amines

Esters of pentavalent phosphorus acids are the most important class of organophosphorus (OP) compounds. They are derivatives of the following three parent acids, viz. phosphinic acid, phosphonic acid and phosphoric acid. Phosphorus compounds may be classified as anhydride, aliphatic, aromatic, and heterocyclic. The majority of OP insecticides are derivatives of phosphoric acid. Triesters of phosphoric acid (phosphates) are considered the prototype of the entire family of OP compounds, in which phosphorous is surrounded by 4 atoms of oxygen. Phosphorothionates (parathion, methyl parathion, diazinon, chlorpyrifos) and phosphorothioates contain a P=S bond. Cationic polyelectrolytes have also been employed for the substrate, which accelerate the hydrolysis. The reactivity of nucleophilic reagents (amines) towards the chlorpyrifos suggested that the reaction proceeds via both nucleophilic and general base catalysis. When substrate is catalysis by amines like ammonia, hydrazine and ethanolamine, etc. suggests that amines also react via nucleophilic attack at phosphorus to catalyze substrate. Nucleophilic cleavage of chlorpyrifos has been reported in the presence of hydroximate nucleophiles to release 3, 5, 6 trichloro 2-pyridinol with second order rate constants. Various amines like ethanolamine, hydrazine, imidazole, n-butylamine and ammonia etc. have been reported to catalyze chlorpyrifos via general base catalysis, in contrast to phosphonate diesters which undergo nucleophilic catalysis by amines. The hydrolytic study of substrate was performed in the presence of amine catalyst, at the temperature of 80oC. The concentration of substrates and amine catalyst in all kinetic runs unless otherwise specified. All the measurement was done on the LC-20AD (ULFA Prominence Liquid Chromatography (Shimadzu) equipped with a UV/Vis detector (HPLC). The Kinetics was found to be of first order with respect to substrate concentration in both the free amine as well as in amine catalyzed reactions. In this study we found that amines catalysis reaction more efficiently at mild acidic regions and ammonia is better catalyst than the other amines. These results are quite encouraging for using ammonia as a powerful decontaminating agent for phosphorothinate ester pesticides at around neutral to slightly acidic pH range i. e. by water from any available source.