RATES AND MECHANISMS OF GAS-PHASE DESUBSTITUTION OF HEXADEUTERIOBENZENE AND BENZENE-DERIVATIVES C6H5CH3, C6H5CF3, C6H5OH, C6H5CL, AND C6H5F BY H-ATOMS BETWEEN 898-K AND 1039-K

Mixtures of C6D6 and C6H5X, X = CH3, CF3, OH, Cl, and F, have been thermolyzed in H2 in a tubular flow system at atmospheric pressure between 898 and 1039 K. Removal of D or X occurs via hydrogen atom attack and lower deuterated benzenes and C6H6 are formed. Mass spectral analyses for (deuterio)benzenes have been used to determine the rates of desubstitution C6H5X + H → C6H6 relative to H + C6D6 → C6D5H (9). For X = D, CH3, CF3, and OH, desubstitution occurs by addition of a H atom to the ring followed by loss of X· from the substituted cyclohexadienyl intermediate. For X = Cl direct abstraction also takes place and for X = F abstraction is the only operative mechanism. No evidence for hydrogen migration around the ring in cyclohexadienyl intermediates was found. On a per-site basis, the dedeuteration rates of C6D6, C6D5H, C6D4H2, ⋯, C6DH5 were found to be equal. On of basis of log k9/L mol-1 s-1 = 10.69 - 2350/2.3T, we have found the following log k(benzene)/L mol-1 for C6H5X + H → C6H6: X = CH3, 10.19 - 2914/2.3T; CF3, 9.79 - 2832/2.3T; OH, 9.93 - 2945/2.3T; Cl, 10.48 - 4148/2.3T; F, 10.31 - 5066/2.3T. Results are compared with relevant literature data. © 1990 American Chemical Society.