Radiolysis of aqueous solutions of cyclopentane and cyclopentene

Abstract

The radiolysis of aqueous solutions of cyclopentane and cyclopentene containing 10"2 N2O or 10"3 M H+ has been studied in considerable detail using 14C radio-gas chromatographic methods. In the studies on cyclopentane the initial yields for production of cyclopentene and dicyclopentyl were found to be, respectively, 1.75 and 1.23 for acidic solutions (where eaq" is converted to H) and 1.95 and 1.36 for those containing N2O (where eaq" is converted to OH). The yields for attack on cyclopentane, 6.0 and 6.7, respectively, for the acidic and N2O containing solutions, agree quite well with the total yields of primary radicals (6.3 and 6.6) so that the material balance is excellent. From the relative yields the disproportionation to combination ratio for reaction between two cyclopentyl radicals in aqueous solution is 1.4 (±0.1). The studies on cyclopentene solutions give a similar ratio for reaction between cyclopentyl and cyclopentyl-2-ol radicals. The product distribution from cyclopentene solutions containing N2O indicates that 23% of the OH radicals attack cyclopentene by abstraction of an allylic H atom and pulse radiolytic studies give a value for this abstraction ~28%. Auxiliary studies on the rates of the radical reactions and on the esr and optical spectroscopic properties of the intermediate radicals are reported. The optical studies show that cyclopentyl radical absorbs only weakly with the absorption decreasing monotonically with increase in wavelength above 215 nm («215 ~1000 M"1 cm-\ esoo ~100 M~1 cm"1). Cyclopentenyl radical, however, exhibits an intense well-defined absorption band at 242 nm («242 2:8000 M~1 cm"1; width at half maximum = 20 nm). In the radiolysis of saturated aqueous solutions of cyclopentane (2.5 X 10"3 M) secondary reactions of H and OH with product cyclopentene become extremely important at doses >1018 eV/g (>3% conversion). For the acidic solutions the cyclopentene reaches a plateau of 3 X 10" 8 M, in accord with expectations from the measured disproportionation-to-combination ratio and the high selectivity (a factor -60) for addition of H to this product. For the N2O containing solutions the cyclopentene reaches a higher level (9 X 10" 5 M) because of the dominant importance of the less selective OH radicals. In general there is very good agreement between the experimental observations on the course of the radiolysis of cyclopentane and predictions based on the yields of radicals produced from the water and the relative rate constants for the different competing reactions which are known either from absolute rate measurements or from the studies on cyclopentene solutions.

Rates of Alkyl Radical-Radical, Alkyl Radical-Iodine, and Iodine Atom-Atom Reactions in Normal Alkanes and Cycloalkanes

“…values for the iodine diffusion coefficients, it was observed that eq 5 does not predict temperature dependences well, but at a given temperature it is found to give excellent results for the different alkanes with x = 0. 5 effective reaction distances for the alkyl radical-iodine scavenging reactions are given in Table 2. The reaction distances appear to decrease from about 0.8 to 0.5 nm with increasing viscosity.…”

Kinetics and anomalous temperature dependence of the kinetic isotope effect of reactions of cycloalkanes C5H10, C6H12 and C6D12 with OH radicals in aqueous solutions

“…The absolute rate constants for reaction (1) have been measured in aqueous solution only for methane [5,6], while relative rate constants in the methane series have been measured for butane [7-10] and cyclopentane [11,12].…”

“…The kinetics of the reactions of OH radicals with saturated hydrocarbons (RH) (1) RH + OH ⋅ ® [R…H…OH] ® R ⋅ + H 2 O including cycloalkanes, has been studied extensively in the gas phase [1]. The absolute rate constants for reaction (1) have been measured in aqueous solution only for methane [5,6], while relative rate constants in the methane series have been measured for butane [7][8][9][10] and cyclopentane [11,12].…”

Cage effect and inverse temperature dependence of the kinetic isotope effect in the c‐C6H12/c‐C6D12 reaction with OH radicals in fenton and HOONOH2O systems

“…In aqueous solutions, these reactions have been investigated for hydrocarbon derivatives, such as alcohols, esters, and carboxylic acids 14–16. In the alkane series, the absolute rate constants have been measured for methane only 17,18 and the relative rate constants have been reported for the methane–butane series 19–22 and cyclopentane 23,24. The most recent data on alkanes and alkane derivatives reactions with OH radicals in water are available in a review 16.…”