The combination of trichloromethyl radicals

zyxwvutsrqp zyxwv zyxw View Article Online / Journal Homepage / Table of Contents for this issue Published on 01 January 1966. Downloaded by Thueringer Universitats Landesbibliothek Jena on 27/10/2014 20:19:19. 140 CHEMICALCOMMUNICAT~ONS The Combination of Trichloromethyl Radicals By J. M. TEDDER and J. C. WALTON (Chemistry Department, Queen’s College, Dundee) The standard rotating-sector technique has been THE rate of combination of trichloromethyl applied to the photochemical addition of bromoradicals to yield hexachloroethane was first trichloromethane to ethylene (details of the reported by Melville, Robb, and Tutton,l from establishment of the reaction mechanism and of the studies of the photochemical addition of bromoexperimental method without the sector have trichloromethane to cyclohexene. Rate measurements were made by dilatometry and the absolute already been reported4). A series of twenty-six rate was determined using the normal rotating runs ([CH,CH,] = 4-40 i< moles l.-I; [CCl,Br] = 1.10 x moles l.-l, temperature 175’; sector method. Very similar studies have been reaction time 3 hours) has been carried out a t reported by Bengough and Thomson.2 The values fourteen different sector speeds (dark :light ratio = for k, 3; max. speed 3787 revs. mins.-l gave a rate ratio kl CCl,. CC1,. ---+ C,Cl, (intermittent : steady) of 0.516; min. speed 0-025 revs. mins.-f gave a rate ratio of 0-233). These determined by both groups of workers was log results have been plotted against the theoretical K , = 8-0 1. moles-l sec.-l a t 2 9 8 ” ~which is two sector curve and an uncorrected value of log KlM8 = powers of ten lower than the combination rates of 10.5 1. moles-l sec.-l has been obtained. Assuming methyl or trifluoromethyl radicals in the gas phase. the reaction has no activation energy this value is No direct measurement of k, has been attempted in a hundred times faster than the previous estimate the gas phase although Goldfinger and co-workers3 for the gas-phase reaction. It brings the combinawere able to make an estimate from studies on the tion of trichloromethyl radicals into line with chlorination of chloroform. Their estimated value methyl, trifluoromethyl, and other alkyl rsdicals.5 log 4 2 9 8 = 8-8 1. moles-l sec.-l was close to the (Received, January 7th, 1966; Corn. 014.) liquid-phase rate of Melville and co-workers. zyxwvutsr zy + zyxwv zyxwvutsr zy zyxwvut H. W. Melville, J. C. Robb, and R. C . Tutton, Discuss. Faraday SOC.,1951, 10, 154. W. I. Bengough and R. A. M. Thomson, Trans. Faraday SUC.,1961,57, 1928. 3 R. Eckling, P. Goldfinger, G. Huybrechts, G. Martens, L. Meyers, and S. Smoes, Ckem. Bey., 1960, 93,3014. 4 J. M. Tedder and J. C. Walton, Trans. Faraday SOL, 1964, 60, 1769. 5 J. A. Kerr and A. F. Trotman-Dickenson, “Progress in Reaction Kinetics”, Vol. 1, p. 107, ed., G. Porter, Pergamon Press, 1961. 2