The photolysis of mixtures of acetone and hexafluoroacetone has been studied in the range 23-240°C. In addition to C2H6, C2F6 and CH3CF3, the products also contained CH2 = CF2.The following reactions are therefore proposed :Reaction (5) as not previously been observed. Defining $* by q5* = kla/k$k$, $* = (2.0f0.2) exp (170f80)/RT. These results indicate that Ela = E2 = E3 4.The product of reaction (la) is a "hot" molecule which can be stabilized to CH3CF3 by collisions. The ratio R C H~C F~/ R C H~= C F~ is dependent on both pressure and temperature. The relative efficiencies of deactivation of CH3CF; by acetone, hexafluoroacetone, nitrogen and perfluorocyclohexane were measured. The Arrhenius parameters have been measured of the various hydrogen abstraction reactions and also of the reaction, CH3 + CF3COCF3 -tCF&OCFs. The I CH3 importance of the reaction, CF3 + CH2=CF;! +CF3-(CH;!-CFz)-is discussed in an appendix.
The reactionsCR3 + CF3+CH3CF3 C H~+ C H~+ C Z H~ CF3 + CF3-+CzF6 have been studied by Pritchard and Dacey,1 who photolyzed mixtures of acetone and hexafluoroacetone, HFA, to generate CH3 and CF3 radicals in the same system. They found the # factor given by to be temperature dependent, and suggested that reaction (3) had an activation energy of 2.14-&0.20 kcal mole-1, assuming that El = Ez = 0. This result was unexpected since for simple radical combinations # is usually independent of temperature 2 and approximately equal to 2 ; Pritchard and Dacey's values of 4 varied in the range 1.8-3.5.Alcock and Whittle 3 studied the reactionThis is so fast that a significant concentration of CH3 radicals was present, consequently the products contained CH3CF3 as well as C2F6 (but not C& because
Hexafluoroacetone has been photolyzed in the presence of CH4, CHsF, CH2F2, CF3CH3, CF2HCF2H and CF3CF2H. Arrhenius parameters are obtained for the abstraction of H by CF3 radicals using the combination of CF3 radicals as a reference reaction. Results were checked by photolysis of hexafhoroacetone in the presence of CD4 plus each of the fluoroethanes and CH4.in turn and using the reaction, CF3+CD4 -+CF3D+CD3, as a reference. The activation energies obtained are compared with those for related series involving abstraction of H by CF3 and CH3 radicals and by bromine atoms.The secondary products of the system CF3+CH2F2 have been measured. For the combination and cross-combination reactions of CF3 and CHF2 radicals, we obtain 4 = 2-4 independent of temperature in the range 291-363°C. It is concluded that the second of the reactionsoccurs to a negligible extent.Previous papers have dealt with the reactions of CF3 radicals with halogenated methanes 1-3 and aromatic halides.4 None of these compounds contained fluorine so we have now studied the reactions of CF3 radicals with fluoromethanes and fluoroethanes ; the results are given in this paper.
EXPERIMENTAL
MATERIALSMost of these were prepared and purified as described e1sewhere.s-7 A sample of CF2= CHF was kindly donated by Prof. Haszeldine of the University of Manchester. C3F8 and n-C4Flo were from Peninsular ChemResearch, Florida, U.S.A. CD4 was made from D20+CCl4+Zn dust by the method of Leblanc et aZ. 8 It was passed through a trap at -80°C into a trap cooled in solid nitrogen. The CD4 was purified by several distillations from -183 to -210°C. Two samples were made which were analyzed by mass spectrometer to contain 96 % CD4, 4 % CD3H and 95 % CD4, 5 % CD3H respectively. Each reactant (except hexafluoroacetone) was freed of possible traces of acids by passing the gas through Carbosorb. All were better than 99 % pure as indicated by i.-r. and g.s.c.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.