Thermal Decomposition of 2-Fluoroethanol: Single Pulse Shock Tube and ab Initio Studies

The thermal decomposition of 2-fluoroethanol (FEOH) has been studied in the temperature range of 1000-1200 K behind reflected shock waves in a single pulse shock tube. The total pressures behind the reflected shocks varied between 13 and 23 atm. The products observed in the covered temperature range are $CH_3CHO$, $C_2H_3F$, $CH_4$, CO, $C_2H_4$, and $C_2H_6$. The unimolecular eliminations of HF and $H_2O$ are found to be the major channels through which 2-fluoroethanol decomposes under these conditions. The rate constant for HF elimination is found to be $10^{13.17\pm0.33}$ $exp[-(59.5\pm1.7)/(RT)] s^{-1}$, and the rate constant for $H_2O$ elimination is found to be $10^{14.30\pm0.34}$ $exp[-(69.7\pm1.7)/(RT)] s^{-1}$, where the activation energies are given in $kcal\hspace {2mm} mol^{-1}$. The $CH_3CHO$ produced by HF elimination through the vinyl alcohol intermediate is chemically active and decomposes leading to $CH_4$ and $CH_3CH_3$ products. The production of ethylene could not be explained from the $CH_3CHO$ pyrolysis mechanism. It is most likely formed directly from the reactant through HOF elimination or by radical processes beginning with C-O bond dissociation. Ab initio (Hartree-Fock [HF] and second-order Mller-Plesset perturbation theory [MP2]) and density functional theory [DFT] calculations have been carried out to find the transition state and activation barrier for HF and $H_2O$ elimination reactions. The HF calculations overestimate the barrier by $18 \hspace {2mm} kcal\hspace {2mm} mol^{-1}$ for HF elimination and $22 \hspace {2mm} kcal\hspace {2mm} mol^{-1}$ for $H_2O$ elimination, and including electron correlation improves the agreement. In particular, DFT predictions for activation energies for HF and $H_2O$ elimination reactions are within $1 \hspace {2mm} kcal\hspace {2mm} mol^{-1}$ of the experimental values