The addition of methyl radicals to fluoroethylenes has been reinvestigated using both azomethane and di-t-butylperoxide as initiators. As in the previous work, excess methyl iodide was added to promote a chain reaction. Unlike the previous study, telomeric products of low volatility were identified and quantitatively estimated. Correction of the monomeric product ratios by addition of the appropriate telomers had a significant effect on the relative Arrhenius parameters in some cases. New values of the activation parameters for the addition of methyl radicals to vinyl fluoride, 1, 1difluoroethylene, trifluoroethylene and tetrafluoroethylene relative to ethylene, are presented.
The rates of addition of trifluoromethyl radicals to each end of propene, l,l,l-trifluoropropene and hexafluoropropene have been determined using a competitive technique, taking as a standard the rate of addition to ethylene. The rate of addition of trifluoromethyl radicals to ethylene (2) has been compared with the rate of combination of trifluoromethyl radicals (6), and a value of kz/ki = (1.6 & 0.2) x lo3 exp (-2 900 f 500 cal mol-'/RT) dm3 mol-3 s* was determined (1 cal =
J).CFs*+ CH2=CHz -+ CF3CHZCH2.(2) CFj*+ CF3* -+ C2Fe.kz ks Since the value of ks is now well established, a new value of the absolute rate of addition of trifluoromethyl radicals to ethylene and to the other olefins can be computed. EXPERIMENTAL Materials were obtained and purified as described previously,1o and were handled on a conventional mercury-free vacuum line. Reactions with ethylene, propene, 1,l ,I-trifluoropropene and hexafluoropropene were carried out in cylindrical Pyrex cells (1 85 and 237 cm3).
Relative Arrhenius parameters have been determined for the addition of trifluoromethyl radicals to vinyl chloride (X=CI), vinyl bromide (X=Br), acrylonitrile (X=CN), methyl vinyl ketone (X=COCH3), Z-methylbut-2-ene, and to iso-butene, taking the rate of addition to ethylene as standard. Addition occurred virtually exclusively a t the unsubstituted end of all the olefins. The relative rates of addition a t 164°C show very little variation. The preexponential terms for addition to the CH2 ends are constant within experimental error, and the small variations in rate are due principally to the activation energy term. The present results are put on an absolute scale using the previously determined Arrhenius parameters for addition to ethylene and are compared with data for other similar monomers determined previously.
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