NUCLEOPHILIC-SUBSTITUTION RATES AND SOLUBILITIES FOR METHYL HALIDES IN SEAWATER

Ozone depletion potentials indicate that methyl bromide is among halog en containing gases which may be scheduled for international level reg ulation. The oceanic component of its global budget is currently unqua ntifiable because of a lack of surface seawater measurements. Given va lues for internal removal and for solubility, marine mixed layer model ling can set bounds for air-sea transfer. Rate constants have been mea sured in seawater, 0.5m NaCl and distilled water for attack on methyl bromide by the chief oceanic nucleophiles chloride ion and H2O, over m uch of the oceanographic temperature range (0-degrees-C to 22-degrees- C). Henry's Law constants have been determined for the same conditions . All results are consistent with classical aqueous phase research adj usted for ionic strength effects. The lifetime of methyl bromide with respect to chemical decay in seawater is three weeks at average surfac e temperatures, and a factor of ten larger and smaller at the extremes . Its dimensionless solubility ranges from 0.1 to 0.3. Analogous exper iments are reported for the other natural methyl halides, CH3Cl and CH 3I.