Henry's Law coefficients of chloropicrin and methyl isothiocyanate

Abstract

Henry's Law coefficients were measured for the first time for chloropicrin and methyl isothiocyanate (MITC) at 25 °C in deionized water, in 0.10 M NaCl, in 0.20 M NaCl, and in pH 4.0 and 8.0 buffered solutions. For chloropicrin, the Henry's Law coefficient was 2.1±0.3 atm M −1, and did not show significant pH dependence or dependence on ionic strength. For MITC, the coefficient was much smaller, 0.06±0.05 atm M −1. The Henry's Law coefficient for MITC did show dependence on ionic strength, increasing to 0.14±0.05 atm M −1 at 0.20 M, but did not appear to depend on pH. MITC has a much stronger tendency to remain in solution than chloropicrin. The transport of chloropicrin from solution to the atmosphere is likely to be significant environmentally, while MITC shows a much lower rate of volatilization. When transferred to the atmosphere, oxidation and photochemical reactions are likely to dominate the transformation of both chloropicrin and MITC, rather than heterogenous reactions.