Trimethyl Phosphite

CAS RN:121-45-9

Environmental Fate

TERRESTRIAL FATE: Trimethyl phosphite hydrolyzes rapidly in the presence of water(1,2) and therefore, adsorption to soil, volatilization from moist soil surfaces, and biodegradation are not expected to be important fate processes(SRC). The hydrolysis rate of trimethyl phosphite is expected to be similar to the hydrolysis rate of triethyl phosphite(SRC). In acid solution (pH=4) triethyl phosphite hydrolyzes immediately forming diethyl phosphite and ethanol(3). At pH 7, triethyl phosphite hydrolyzes completely within 20 minutes; after 3 hours 89.3% diethyl phosphite and 10.7% monoethyl phosphite are formed(3). At pH 9, the half-life of triethyl phosphite in water is approximately 5.1 hours; 70% of the substance remains unhydrolyzed after 3 hours(3). Trimethyl phosphite is expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 24 mm Hg at 25 deg C(4). Dimethyl phosphite, an hydrolysis product of trimethyl phosphite, reached 48% of its theoretical BOD in 4 weeks in the Japanese MITI test indicating it is inherently biodegradable, but not readily biodegradable(1).
AQUATIC FATE: Trimethyl phosphite hydrolyzes rapidly in the presence of water(1,2) and therefore, adsorption to sediment, volatilization from water surfaces, bioconcentration and biodegradation are not expected to be important fate processes(SRC). Trimethyl phosphite hydrolyzes in water to form dimethyl phosphite and methanol(1,2). The hydrolysis rate of trimethyl phosphite is expected to be similar to the hydrolysis rate of triethyl phosphite(SRC). In acid solution (pH=4) triethyl phosphite hydrolyzes immediately forming diethyl phosphite and ethanol(3). At pH 7, triethyl phosphite hydrolyzes completely within 20 minutes; after 3 hours 89.3% diethyl phosphite and 10.7% monoethyl phosphite are formed(3). At pH 9, the half-life of triethyl phosphite in water is approximately 5.1 hours; 70% of the substance remains unhydrolyzed after 3 hours(3). Dimethyl phosphite, an hydrolysis product of trimethyl phosphite, reached 48% of its theoretical BOD in 4 weeks in the Japanese MITI test indicating it is inherently biodegradable, but not readily biodegradable(1).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), trimethyl phosphite, which has a vapor pressure of 24 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase trimethyl phosphite is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 33 minutes(SRC), calculated from its rate constant of 7.1X10-10 cu cm/molecule-sec at 25 deg C(3). Trimethyl phosphite does not absorb at wavelengths >290 nm(4) and therefore is not expected to be susceptible to direct photolysis by sunlight(SRC).
Find more information on this substance at: Hazardous Substances Data Bank , TOXNET , PubMed