Rate Constants for Hydrogen Atom Attack on Some Chlorinated Benzenes at High Temperatures

Article abstract of DOI:10.1021/j100339a043

Hydrogen atoms from the decomposition of hexamethylethane were reacted with chlorobenzene, o-dichlorobenzene, p-dichlorobenzene, and 1,2,3-trichlorobenzene in the presence of toluene or 1,3,5-trimethylbenzene in single-pulse shock tube experiments.Using the rate expression for the displacement of the methyl group from the methylated aromatics as standards we find k(H + C6H5Cl -> C6H6 + Cl) = (2.2E10) exp(-4531/T) L/(mol*s), k(H + o-C6H4Cl2 -> C6H5Cl + Cl) = (9.2E10) exp(-5196/T) L/(mol*s), k(H + p-C6H4Cl2 -> C6H5Cl + Cl) = (4.6E10) exp(-4541/T) L/(mol*s), k(H + 1,2,3-C6H3Cl3 -> o-C6H4Cl + Cl) = (1.9E10) exp(-2954/T) L/(mol*s), and k(H + 1,2,3-C6H3Cl3 -> m-C6H4Cl + Cl) = (3.7E9) exp(-1856/T) L/(mol*s) at temperatures of 1050-1150 K and pressures between 2.5 and 3.2 atm.In this temperature range the relative rate constants on a per-chlorine basis for the five processes are 1:1.15:1.05:1.8:2.4.The absolute uncertainty in the rate expressions are of the order of 8 kJ in the activation energy and a factor of 2.5 in the A factor.The relative rate constants have an uncertainty of no more than a factor of 1.1.Rate expressions for the reverse chlorination process have been calculated to be k(Cl + C6H6 -> C6H5Cl + H) = (4.7E10) exp(-13453/T) L/(mol*s), k(Cl + C6H5Cl -> o-C6H4Cl2 + H) = (2.9E10) exp(-15075/T) L/(mol*s), and k(Cl + C6H5Cl -> p-C6H4Cl2 + H) = (8.8E9) exp(-13614/T) L/mol*s.