2,4-Toluene Diisocyanate

CAS RN:584-84-9

Environmental Fate

TERRESTRIAL FATE: 2,4-Toluene diisocyanate reacts readily with compounds containing active hydrogens, such as water, acids, and alcohols(1). 2,4-Toluene diisocyanate is not expected to volatilize from dry soil surfaces(SRC) based upon a vapor pressure of 8X10-3 mm Hg(2). Based on data for the mixture toluenediisocyanate (TDI) (2,4- plus 2,6-isomers), 2,4-toluene diisocyanate may not be stable in the terrestrial environment(SRC). In a simulated spill, 5 kg of TDI in a container was covered with 50 kg of sand and 5 kg of water at ambient temperatures and samples taken from the top and bottom of the sand pile(3). After 24 hr, 5.5% of the TDI remained unreacted and after 8 days 3.5% remained(5). The reaction product was largely polyureas(3). Ten days after a spill of 13 tons of TDI onto a swampy, wet forest soil, TDI and toluenediamines were found in the soil(2,3). The TDI solidified and the area was covered with sand. The soil concentration of TDI and toluenediamine combined declined from the parts per thousand to parts per million range between 10 days and 12 weeks after the spill(3). One year later, neither TDI nor toluenediamine could be found in soil samples(4). After 6 years, only TDI-derived polyureas were found at the site in soil samples at depths to 100 cm(4). A 0% theoretical BOD for 2,4-toluene diisocyanate incubated four weeks using an activated sludge inoculum in the Japanese MITI test(5) suggests that biodegradation of 2,4-toluene diisocyanate is not an important environmental fate process in soil(SRC).
AQUATIC FATE: 2,4-Toluene diisocyanate reacts readily with compounds containing active hydrogens, such as water, acids, and alcohols(1). Based on data for the mixture, 2,4-toluene diisocyanate may not be stable in the aquatic environment(SRC). When low concentrations of toluene diisocycanate (TDI) are released into model river or seaway systems, it hydrolyzes within a day(2). An experiment was performed to simulate a spill into running water by pouring 0.5 liter of TDI into 20 liters of slowly overflowing water(3). Barely detectable amounts of toluenediamine were present in the overflow samples. As in the stagnant water simulation, a crust formed that contained <0.5% of the original TDI after 35 days(3). A 0% theoretical BOD for 2,4-toluenediisocyante incubated four weeks using an activated sludge inoculum in the Japanese MITI test(4) suggests that biodegradation is not an important environmental fate process in water(SRC).
ATMOSPHERIC FATE: According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), 2,4-toluene diisocyanate, which has a vapor pressure of 8X10-3 mm Hg at 25 deg C(2), is expected to exist solely as a vapor in the ambient atmosphere. Vapor-phase 2,4-toluene diisocyanate 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 1.7 days(SRC), calculated from its rate constant of 6.3X10-12 cu cm/molecule-sec at 25 deg C(SRC) determined using a structure estimation method(3). Atmospheric degradation may also occur through contact with clouds, fog or rain. 2,4-Toluene diisocyanate does not contain chromophores that absorb at wavelengths >290 nm(4), and therefore is not expected to be susceptible to direct photolysis by sunlight(SRC).
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