Dimethyl phosphonate

Hydrolysis

Description of key information

DT50 = 470 h (pH 4, 23 °C)
DT50 = 3.09 h (pH 7, 23 °C) 
DT50 < 1 min (pH 9, 23 °C)

Additional information

A guideline study to investigate the stability of dimethyl phosphonate in water was conducted by the Bayer AG (2002). The study shows that dimethyl phosphonate is hydrolysed rapidly to moderately fast in water depending on the pH. The study is in accordance with the principles of Good Laboratory Practice (GLP) and was conducted according to the directive 92/69/EEC, method C.7 using 31-Phosphorous-NMR for analysis. Incubations were performed in buffered water at 23 °C. Dimethyl phosphonate is hydrolysed faster in basic solution than at lower pH. The dissipation half-life of dimethyl phosphonate was determined to be 470 h at pH 4, 3.09 h at pH 7 and less than 1 minute at pH 9. The primary degradation products at every pH value were monomethyl phosphonate and methanol (Bayer AG, 2002).

In a study on the stability of tri-, di- and monomethyl phosphonate in unbuffered water without control of pH, the hydrolytic loss of tri- and dimethyl phosphonate and the formation of monomethyl phosphonate were monitored. Half-life of dimethyl phosphonate was estimated to be 60 h. After 6 days 100% of dimethyl phosphonate was degraded. In the first phase of the incubation monomethyl phosphonate was the only detected hydrolysis product, but starting after 74 h of incubation, phosphonic acid was also detected. The stability of monomethyl phosphonate was investigated by continuing the analysis of the dimethyl phosphonate hydrolysis. After 6 days (100% degradation of dimethyl phosphonate) 85% of the initial dimethyl phosphonate was recovered as monomethyl phosphonate, another 15% was degraded supposably to phosphonic acid. After 10 days 68% monomethyl phosphonate were found and another 32% were supposed to be degraded to phosphonic acid. It was concluded that monomethyl phosphonate is hydrolysed more slowly than dimethyl phosphonate (Bayer AG, 1992).