Rate Determination of 1,1-HCl vs. 1,2-DCl Elimination from CD3CD2CHCl2

Allie Larkin


Hydrochlorofluorocarbons (HCFCs) have become ubiquitous in the chemical industry and in many commercial operations since they replaced chlorofluorocarbons (CFCs). The Montreal Protocol requires HCFCs to be phased out by 2030 worldwide. Therefore HCFCs need to be discarded and destroyed or converted into feedstock useful to the chemical industry. Computational models can be developed to evaluate the synthetic utility of potential conversion processes of halocarbons to commercially feasible materials. For these calculations of complex kinetic schemes to be reliable, accurate kinetic parameters are needed for all decomposition pathways. Degradation mechanisms of HCFCs include: interchange, stabilization and elimination (1,1-HX and 1,2-HX, where X = F or Cl). The 1,1-HX elimination pathway has not been widely studied. Therefore the contribution of 1,1-HX elimination to the formation of a carbene is unknown for most HCFCs. This research focuses on the model compound 1,1-dichloropropane and will determine ratios of the molecule’s degradation pathways. Vibrationally excited CD3CD2CHCl2 molecules were generated via recombination of CD3CD2 and CHCl2 radicals prepared from CD3CD2I and CHCl3. 1,1-HCl and 1,2-DCl elimination were observed and their individual rate constants were measured for production of both cis- and trans-1-chloropropene for each pathway. The four major products were Z-CD3CD=CHCl and E-CD3CD=CHCl (both the result of 1,2-DCl loss), and Z-CD3CD=CDCl and E-CD3CD=CDCl (both the result of 1,1-HCl loss), with a total experimental rate constant of 3 x 107 s-1. The 1,1-HCl elimination reaction initially formed the CD3CD2CCl carbene that underwent D-migration to give either Z- or E-CD3CD=CDCl. The branching fraction for the 1,1-HCl versus 1,2-DCl elimination reactions was 0.15. The Z/E-CD3CD=CHCl branching ratio for 1,2-DCl loss is 1.8. However, the Z/E-CD3CD=CDCl declined from 3 at the highest pressures to 1.8 at lower pressures as the Z-isomer was preferentially formed from the carbene and some of the Z-CD3CD=CDCl had sufficient energy to isomerize to the E-isomer.


Gas Phase Kinetics; Hydrochlorofluorocarbons; Environment

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