DECOMPOSITION OF PHOSPHONATE ESTERS ADSORBED ON ALUMINUM-OXIDE

Inelastic electron tunneling spectroscopy has been used to examine the adsorption and reaction of three phosphonate esters on aluminum oxide surfaces which were synthesized by the plasma oxidation of metallic aluminum films. The phosphonate esters were diisopropyl methylphosphonate (DIMP), dimethyl methylphosphonate (DMMP), and diphenyl methylphosphonate (DPMP). The adsorption temperatures ranged from 200 to 673 K. The exposures of gaseous DIMP and DMMP were 1. 0 torr multiplied by (times) s, while DPMP was exposed to the surface as a 0. 025 M solution in hexane. DIMP was found to adsorb molecularly in low coverages at 295 K, whereas at 373 K, DIMP was found to adsorb dissociatively in low coverages as isopropyl methylphosphonate. Above 373 K the isopropyl methylphosphonate decomposed to the metastable hydroxy methylphosphonate, which, in turn, decomposed completely to the methylphosphonate above 573 K.