1,1-Difluoroethene

CAS RN:75-38-7

Environmental Fate

TERRESTRIAL FATE: Based on a classification scheme(1), an estimated Koc value of 32(SRC), determined from a structure estimation method(2), indicates that 1,1-difluoroethene is expected to have very high mobility in soil(SRC). Volatilization of 1,1-difluoroethene from moist soil surfaces is expected to be an important fate process(SRC) given an estimated Henry's Law constant of 0.4 atm-cu m/mole(SRC), based upon its vapor pressure, 3X10+4 mm Hg(3), and water solubility, 169 mg/L(4). 1,1-Difluoroethene is expected to volatilize from dry soil surfaces(SRC) based upon its vapor pressure(3). Highly chlorinated/fluorinated compounds are not expected to biodegrade rapidly(5).
AQUATIC FATE: Based on a classification scheme(1), an estimated Koc value of 32(SRC), determined from a structure estimation method(2), indicates that 1,1-difluoroethene is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is expected(3) based upon an estimated Henry's Law constant of 0.4 atm-cu m/mole(SRC), derived from its vapor pressure, 3X10+4 mm Hg(4), and water solubility, 169 mg/L(5). Using this Henry's Law constant and an estimation method(3), volatilization half-lives for a model river and model lake are 2.3 hours and 3.2 days, respectively(SRC). According to a classification scheme(6), an estimated BCF of 3(SRC), from its log Kow of 1.24(7) and a regression-derived equation(8), suggests the potential for bioconcentration in aquatic organisms is low(SRC). Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions(3). Highly chlorinated/fluorinated compounds are not expected to biodegrade rapidly(9).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), 1,1-difluoroethene, which has a vapor pressure of 3X10+4 mm Hg at 25 deg C(2), is expected to exist solely as a gas in the ambient atmosphere. Gas-phase 1,1-difluoroethene 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 8 days(SRC), calculated from its rate constant of 2.1X10-12 cu cm/molecule-sec at 25 deg C(3). Gas-phase 1,1-difluoroethene is also degraded in the atmosphere by reaction with ozone(SRC); the half-life for this reaction in air is estimated to be 57 days(SRC), calculated from its rate constant of 2.0X10-19 cu cm/molecule-sec at 25 deg C(4). 1,1-Difluoroethene does not contain chromophores that absorb at wavelengths >290 nm(5) 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