Cyclohexane radiation chemistry

Dewkurst, H. A. Radiation chemistry of n-hexane and cyclohexane liquids. J. chem. Physics 24, 1254 (1956). 

Following the realisation that the reactions of the hydrated electron played an important role in the radiation chemistry of liquid water it was not long before evidence was sought, and found, that the electron and the counter cation could be involved in chemical reactions in non-polar liquids before they underwent neutralisation. Scholes and Simic (1964(49)) showed that on irradiation of solutions of nitrous oxide in hydrocarbons nitrogen was formed in the dissociative attachment reaction analogous to reaction (6). Similarly, Buchanan and Williams (1966(50)) attributed the formation of HD in Y lrradiated solutions of C2H3OD in cyclohexane to the transfer of a... 

Rzad and Schuler" studied the radiation chemistry of a solution of " C-cyclopropane in hexane over the concentration range 10 " to 10 M. The main radioactive products, which appear to result from ion molecule reactions, are propane formed by H2 transfer (50 %) and by H transfer (20 %) and mixed nonanes (30 %) formed by the addition of CaHg unit to a hexyl ion. At the lower concentrations, very pronounced dose dependence of the yields was observed. This was ascribed to a competitive formation of olefins in the radiolysis. For cyclopropane-cyclohexane solutions the chemical processes seem to be considerably more complicated. The observed yield of total radioactive products extrapolated to zero concentration of cyclopropane are 0.05 and 0.11 G units for hexane and cyclohexane, respectively. These limiting yields are of the order of magnitude of and appear to be related to, the free ion yields in these systems. Since cyclopropane was found to react with hydrocarbon ions" it is used quite often as a scavenger for positive ions, as in the work of Davids and coworkers . 

Many studies used radiation chemistry to produce the radical and radical cations and anions of various dienes in order to measure their properties. Extensive work was devoted to the radical cation of norbomadiene in order to solve the question whether it is identical with the cation radical of quadricyclane . Desrosiers and Trifunac produced radical cations of 1,4-cyclohexadiene by pulse radiolysis in several solvents and measured by time-resolved fluorescence-detected magnetic resonance the ESR spectra of the cation radical. The cation radical of 1,4-cyclohexadiene was produced by charge transfer from saturated hydrocarbon cations formed by radiolysis of the solvent. In a similar system, the radical cations of 1,3- and 1,4-cyclohexadiene were studied in a zeolite matrix and their isomerization reactions were studied. Dienyl radicals similar to many other kinds of radicals were formed by radiolysis inside an admantane matrix. Korth and coworkers used this method to create cyclooctatrienyl radicals by radiolysis of bicyclo[5.1.0]octa-2,5-diene in admantane-Di6 matrix, or of bromocyclooctatriene in the same matrix. Williams and coworkers irradiated 1,5-hexadiene in CFCI3 matrix to obtain the radical cation which was found to undergo cyclization to the cyclohexene radical cation through the intermediate cyclohexane-1,4-diyl radical cation. 

The resistance of benzene to radiation damage is reflected in G(H2) 0.004 pmol J" it is more than 100-fold less than the yield in cyclohexane. Other decomposition products are formed in similarly low yields and the radiation chemistry of benzene is dominated by its lowest singlet ( B ) and triplet ( B ) excited-state molecules. By adding suitable solutes the... 

Multiphotonic photolysis of perylene and pyrene in liquid cyclohexane shows that ArCy ion pairs are involved. This piece of work is very relevant to understanding reactions which are involved in the allied discipline of radiation chemistry. 

Emission measurement from the excited states is also a powerful method to investigate the ion beam radiation chemistry because a very sensitive time resolved photon-counting technique can be applied. In 1970s, temporal behavior of the emission from benzene excited states in 40 mM benzene in cyclohexane irradiated with pulsed proton and He ion particles was measured and compared with UV pulse irradiation. It was found that immediately after the irradiation there is a short decay (< 10 ns) followed by a longer decay corresponding to the life-time of the benzene excited states (26-28 ns). The fraction of the shorter decay component increases with increasing LET of the particle. This was explained by a quenching mechanism that radical species formed in the track core attack and quench the benzene excited states, which would take place only shorter period less than 10 ns after irradiation [69]. 

In the following we shall discuss the radiation chemistry of methane in the gas phase, which may serve as an illustration of the various aspects of the radiation chemical effects in the gas phase. We shall also consider the effect of pressure and dose rate on the competition of the various processes. Finally we shall discuss briefly the effect of pressure on the fragmentation in cyclohexane. For a more detailed study the reader is referred to the review article of Gyorgy and the references cited therein. 

In the following we first discuss the charge separation. Next, we consider some examples of the chemistry of the ions and of the excited states formed after recombination. Then we shall discuss the overall product formation for cyclohexane and n-pentane and indicate some general features of the decomposition of the various saturated hydrocarbons. All this work concerns the radiolysis with low LET radiation (gamma radiation, fast electrons). In the last section we give some results for radiation with different LETs for the case of cyclohexane. We also indicate how the non-homogeneity in the initial spatial distribution of the reactive species is accounted for in the (non-homogeneous) kinetics. 

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