Kinetics of α- and β-Hydrogen Abstraction from C2H5Cl by Br Atoms. Estimate of C-H Bond Dissociation Energies and Heats of Formation of CH3CHCl and CH2CH2Cl Radicals

Article abstract of DOI:10.1021/j100365a037

The gas-phase photobromination of ethyl chloride has been investigated over an extended temperature range in the presence and absence of ethane as external competitor.The rate constant for α-hydrogen abstraction in CH3CH2Cl was redetermined relative to C2H6 between 40 and 150 deg C.The abstraction of β-hydrogen was measured in the internal competition in the range 70-150 deg C by use of electron capture detection.The relative rates were combined with the known rate parameters for the bromination of C2H6 A/cm³mol^-1s^-1)=14.14+/-0.06, E=13.66+/-0.14 kcalmol^-1> to obtain the absolute rate constants (cm³mol^-1s^-1)k(α)=E(12.71+/-0.06)exp<-(9.95+/-0.14)/RT> and k(β)=E(12.60+/-0.07)exp<-(14.14+/-0.15)/RT>, where the activation energies are expressed in kcal mol^-1.From an assessment of thermochemical and kinetic data the following radical heats of formation and C-H bond dissociation energies (kcal mol^-1) in C2H5Cl have been obtained: ΔH_f deg (CH3CHCl) = 17.6+/-1, D deg (CH3CHCl-H)=96.5+/-1 and ΔH_f deg (CH2CH2Cl)=21.8+/-1, Ddeg (CH2ClCH2-H)=100.7+/-1.These results compare satisfactorily with recent determinations by the monoenergetic electron impact method.

Full text of DOI:10.1021/j100365a037

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