The thermal dehydrochlorination CF,CICH, + CFFCH, + HCl has been studied in a static system between 637 and 758 K. It is a homogeneous, molecular first-order reaction and its rate constant is given by log,, (k, s-') = -(53,400 2 100)/4.576T + (12.21 ? 0.03) This reaction has also been studied in the presence of CCl, and mixtures of CCl, and HCl between 585 and 662 K. It is then accelerated and the initial rate increase is given by with log,, (k', L1" /mo11'2 1 s) = -(41,650 t 180)/4.576T + (10.84 ? 0.06) and log,, k" = (7900 ? 180)/4.576T -(0.59 ? 0.06). A radical chain mechanism is shown to be consistent with these latter results.

The title reaction has been studied in a static quartz reaction vessel between 587 and 658 K at pressures between 40 and 152 torr. The dehydrochlorination is the only significant reaction and is autoaccelerated by the produced HC1. Numerical modelling indicates that the Rice-Herzfeld mechanism, generally used for describing the pyrolysis of halogenated ethanes, has to be completed in the case of CC13CH3 with additional transfer reactions converting "dead' radicals into chain carriers and vice-versa. The numerical simulation fits the experimental results, in the absence as well as in the presence of different amounts of added HCI. The dehydrochlorination is also accelerated by the addition of CCl,,, which can be explained in terms of additional elementary steps involving . CC13 radicals.

Numerical integrations of a hypothetical radical chain reaction model have been performed for the pyrolysis of CHzClCH3 which is known to be molecular. Analyses of the modelling results have led to a better understanding of the participation (or nonparticipation) of "dead" radicals in the self-inhibition of the radical chain reaction. Attention is focused on the fact that apparently slow elementary reactions still may have to be taken into account in a pyrolysis mechanism when they produce "dead" radicals which can accumulate. CH2ClCH3 --+ C2H4 + HCI has all the characteristics of a pure molecular reaction. Further, the Arrhenius parameters measured by the different authors are in good agreement. The mean value of the activation energy is 56.6 kcal/mol and that for the pre-exponential factor is 1013.5 s-' between 670 and 770 K.The absence of a radical chain pyrolysis was attributed in 1949 by Barton [lo] to the fact that the C1-attack on CH2C1CH3 predominantly yields the CHC1CH3 radical and only minor amounts of the CH2CH2C1 radical 2 (2)The "dead" radical .CHClCH3 is unable to propagate the chain by split-off of a C1-atom, thus explaining the absence of a radical chain pyrolysis. Experimental kinetic results for the kz/k3-ratio' reported after 1949 contradict the theory of Barton: the C1-attack on CH2CICH3 yields about 70% CHC1CH3 radicals and 30% CH2CH2C1 radicals. Martens [131 states that the inhibition is not to be attributed to the absence of CH2CHZC1 radicals but to the inhibitory effect of the "dead" radical CHClCHS. This radical would disappear essentially by reaction with the C1-atom chain carrier, thus, giving rise to chain inhibition. 'Absolute values of 3.2 and 2.0 for the kzlks-ratio at 690 K can be calculated from the kinetic parameters reported in 1111 and [121, respectively. This ratio does not depend significantly on the temperature.

The thermal reactions of 1,3-butadiene (BD) with cyclohexa-1,3-diene (CHD) have been studied in a static system between 437 and 526 K. The pressures of BD and CHD were varied from 61 to 397 torr and from 50 to 93 torr, respectively. The percentages of consumed BD and CHD were always kept lower than 14%. The reactions-in the order of importanceare A thermochemical analysis of a biradical mechanism is in agreement with these results.

The kinetics of the thermal reactions of bicyclo[4.2.2]deca-3;7-diene (BDD) and endo-and exo-5-vinylbicyclo[2.2.2]oct-2-ene (endo-and exo-VBO) have been studied in the gas phase.The temperature range was 459-526 K for BDD, 476-563 K for endo-VBO, and 513-578 K for exo-VBO. The initial pressures were varied from 2 to about 40 torr. These compounds where the superscripts represent the reagents and the subscripts the products. The heats of formation and the entropies of endo-VBO, exo-VBO, and BDD are estimated.