The thermal decomposition of 1,1,2-trifluoroethane between 1100 and 1250°K gives three isomeric difluoroethylenes as the major carbon-containing products. The rate constants for the three molecular elimination processes CH2FCHF2 -CH2CF2 + HF (fei), CH2FCHF2 -* trans-CHFCHF + HF (k2), and CH2FCHF2 -*• czs-CHFCHF + HF (£3) have been evaluated to be log (¿i/sec-1) = 13.0 ± 0.5 -(65.4 ± 2.6)/2.303RT, log (fe2/sec~4) = 14.1 db 0.5 -(69.1 ± 2.9)/2.303fiT, and log (fcg/sec-1) = 13.5 ± 0.5 -(64.5 ± 2.61/2.303RT where R is in kcal mol-1. The experimental Arrhenius parameters were found to be in good agreement with those predicted theoretically using a modified semiion pair model. The observed differences in the three rate constants can be explained in terms of intramolecular interactions of the ñuorine atoms.

An estimate of the extent of the aa-elimination of H F in 1,l-difluoroethane is obtained from a study of the shock-tube pyrolysis of the deuteriated isomer, CH3CDF,

The pyrolysis of 2,2-dichloro-l , 1 ,I-trifluoroethane was studied over the temperature range of 112(tI26OoK at total reflected shock pressures from -2800 to 3100 torr. Below 1260"K, the decomposition leads to three reaction products which were identified as CF&FCI, CF&FH, and CF3CC13. The results are interpreted in terms of a parallel C-C1 bond rupture process which becomes competitive with the molecular HCI elimination. 'The rate constant for the *,a-elimination process CF3CHC12 + CFzCFCl $-HC1 has been deduced to be log (klm/sec-') = (13.4 f 0.7) -(63.1 f 3.8 kca1)/2.303RTIt was also possible to obtain the overall rate constant for the formation of CFZCFH, which is given by log (k"/sec-') = (1 1.5 f 0.8) -(54.1 i 4.5 kca1)/2.303RTSome evidence for hydrogen fluoride elimination was found at temperatures above 1260°K. However, at these higher temperatures C-C bond scission also occurs and the kinetics of the system become untractable.

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