The reactivity of chlorine atoms in aqueous solution. Part III. The reactions of Cl-center dot with solutes

Laser flash photolysis of chloroacetone was used to measure the rate constants and activation energies for the reactions of the Cl-. atom with a number of oxygen-containing compounds and inorganic anions in aqueous solution. For the organic compounds there is a strong correlation at 25 degrees C between k(Cl-. + RH) and k((OH)-O-. + RH), where RH is CH3OH, CH3CH2OH, CH3CH(OH)CH3, (CH3)(3)COH, HCHO, CH3CHO, CH3CO2H, HCO2H and HCO2-, respectively. For CH3CO2-, k(Cl-. + RH) >> k((OH)-O-. + RH), and for CH3COCH3 and CH3COCH2Cl, k(Cl-. + RH) << k((OH)-O-. + RH). Possible reasons for these differences are discussed in terms of preferential attack by Cl-. at O-H groups in the neutral molecules, rather than H-abstraction from C-H as with (OH)-O-., and electron transfer for the reactions of Cl-. with the anions. For the inorganic anions X = OCN-, NO3-, SO42-, ClO3-, SCN-, HCO3-, N-3(-), NO2-, HSO3, k(Cl-. + X) ranges from 1.0 x 10(8) (NO3-) to 5.3x10(9) dm(3) mol(-1) s(-1) (SCN-) but there is no strong correlation between k and the reduction potential of X. Comparison of the reactivity of Cl-. with reported rate constants for the reactions of Cl-2(.-) indicates that, in many cases, these rate constants are largely accounted for by the fraction of Cl-. present in equilibrium with Cl-2(.-). The implications of these results for atmospheric chemistry are discussed.