Laboratory Determination of the Carbon Kinetic Isotope Effects (KIEs) for Reactions of Methyl Halides with Various Nucleophiles in Solution
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- Baesman, S.M. & Miller, L.G. J Atmos Chem (2005) 52: 203. doi:10.1007/s10874-005-1904-0
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Large carbon kinetic isotope effects (KIEs) were measured for reactions of methyl bromide (MeBr), methyl chloride (MeCl), and methyl iodide (MeI) with various nucleophiles at 287 and 306 K in aqueous solutions. Rates of reaction of MeBr and MeI with H2O (neutral hydrolysis) or Cl− (halide substitution) were consistent with previous measurements. Hydrolysis rates increased with increasing temperature or pH (base hydrolysis). KIEs for hydrolysis were 51 ± 6%0 for MeBr and 38 ± 8%0 for MeI. Rates of halide substitution increased with increasing temperature and greater reactivity of the attacking nucleophile, with the fastest reaction being that of MeI with Br−. KIEs for halide substitution were independent of temperature but varied with the reactant methyl halide and the attacking nucleophile. KIEs were similar for MeBr substitution with Cl− and MeCl substitution with Br− (57 ± 5 and 60 ± 9%0, respectively). The KIE for halide exchange of MeI was lower overall (33 ± 8%0) and was greater for substitution with Br− (46 ± 6%0) than with Cl− (29 ± 6%0).