Catalytic Oxidation of Dimethyl Methylphosphonate

Article abstract of DOI:10.1006/jcat.1994.1075

The catalytic oxidation in air of dimethyl methylphosphonate (DMMP), a nerve gas stimulant, has been studied over laboratory-prepared Pt/Al2O3 as a function of Pt loading (0.5 or 2.0percent) and temperature (150, 250, or 400 deg C).At 250 deg C and residence time of 0.69 s, carbon balances indicate that 90-95percent of the C atoms in the DMMP feed were completely oxidized to CO2 during the periods when DMMP destruction was > 99percent (50 h for the 0.5percent Pt catalyst and 76 h for the 2.0percent Pt catalyst).Only after the end of these protection periods was methanol detected in the gaseous effluent.HPLC analysis of a product liquid showed that four intermediate P-containing compounds were formed: dimethyl phosphate (DMP), monomethyl phosphate (MMP), monomethyl methylphosphonate (MMMP), and methylphosphonic acid (MPA).A reaction scheme is proposed to account for the production of these intermediates by a series of oxidative and hydrolytic reactions.Different behavior was observed at 400 deg C.Although the period of complete DMMP destruction was very long ( > 135 h) with 0.5percent Pt catalyst, oxidation as measured by CO2 production was incomplete and the oxidation activity decreased with time on stream.At 400 deg C the hydrolytic reactions apparently become sufficiently efficient to effect complete DMMP conversion for extended periods despite the drop in oxidation activity.Several methods of characterizing deactivated catalyst provide incremental evidence that catalyst alumina reacts with product phosphoric acid to give AlPO4.