Determination of Rate Constants for Aqueous Reactions of HCFC-123 and HCFC-225ca with OH~-Along with Henry's Law Constants of Several HCFCs

摘要

Henry's law constants of six kinds of hydrochlorofluorocarbons (HCFCs) were determined at 313-353 K by means of a phase-ratio variation headspace method: K_H = K_H~(353)exp(-ΔH_(sol)/R(1/T -1/353)) and (K_H~(353) in M atm~(-1), ΔH_(sol) in kJ mol~(-1)) = (0.0070 ± 0.0006, -23 ± 2), (0.0038 ± 0.0011, -22 ± 10), (0.0065 ± 0.0007, -21 ± 3), (0.0026 ± 0.0007, -23 ± 8), (0.0016 ± 0.0003, -30 ± 4), and (0.0022 ± 0.0003, -25 ± 4), respectively, for HCFC-141b (CH3CCl2F), HCFC-142b (CH3CClF2), HCFC-123 (CF3CHC12), HCFC-124 (CF3CHCIF), HCFC-225ca (CF3CF2CHCl2), and HCFC-225cb (CClF2CF2CHClF). Errors represent two standard deviations only for the fitting. The decay of headspace partial pressures of these HCFCs via hydrolysis was discerned only for CF3CHCl2 and CF3CF2CHC12 under the experimental conditions examined. Rate constants (k_(OH~-) in M~(-1) s~(-1)) for aqueous reactions of CF3CF2CHC12 and CF3CHC12 with OH~- at 313-353 K were determined to be (0.57±0.04)exp(-(11, 300±600) × (1/T - 1/353)) and (2.9±0.2) × 10~(-4)exp(-(8800±900) × (1/T - 1/353)), respectively, from monitoring changes in headspace partial pressure over prescribed concentrations of aqueous NaOH as a function of the headspace time duration and concentration of aqueous NaOH. The calculations performed included consideration of gas-water equilibrium and hydrolysis at both headspace and room temperatures. The calculation for CF3CHCl2 also included consideration of salting-out effects. The salting coefficient of NaCl on a natural log basis was determined to be 0.36 ± 0.06 M~(-1), and this value was used for consideration of the salting-out effect of NaOH. Whereas the activation energy for CF3CF2CHCl2 was greater than that for CF3CHC12, the k_(OH~-) value at 353 K of CF3CF2CHC12 was 103 times larger than that of CF3CHCl2, indicating that reaction mechanisms for these two HCFCs differed from each other. The aqueous reaction of CF3CF2CHC12 with OH~- was found to proceed through dehydrofluorination on the basis of detection of CF3CF=CCI2 as a primary degradation product of the reaction and proportionality of the rate constants to both concentrations of CF3CF2CHCl2 and OH~-.