ADDITION OF CYCLOPENTANE TO SLOWLY REACTING MIXTURES OF H-2+O-2 BETWEEN 673 AND 783 K - REACTIONS OF H AND OH WITH CYCLOPENTANE AND OF CYCLOPENTYL RADICALS

A number of elementary reactions involved in the oxidation of cyclopentane (CP) have been studied by adding CP to H-2-O-2 mixtures over the temperature range 673-783 K. Kinetic studies of the relative rates of consumption of CP and H-2 have given values of k(21) = (1.11 +/- 0.25) x 10(10) and k(22) = (1.84 +/- 0.32) x 10(9) dm(3) mol(-1) s(-1) at 753 K. Combination with independent data and critical analysis gives k(21) = 3.65 x 10(2) T-2.5 exp(519/T) dm(3) mol(-1) s(-1), which is recommended between 250 and 1500 K, with error limits of <20%. Similarly, k(22) = 2.4 x 10(6) T-1.5 exp(-2440/T) dm(3) mol(-1) s(-1) is recommended between 300 and 1250 K. OH + c-C5H10 --> c-C5H9 + H2O (21) H + c-C5H10 --> c-C5H9 + H-2 (22) Analytical studies over a range of mixture compositions have shown that the major initial products are c-pentane, 1,2-epoxycyclopentane, acrolein and, at low [O-2] C2H4. The mechanism of oxidation is essentially similar to that of linear alkanes and of cyclohexane, although the different stereochemistry of the two rings has a significant influence on parts of the mechanism. In particular, in the range 673-783 K and at [O-2] > 50 Torr, very little ring rupture has been observed in the initial products. The formation of C2H4 has been discussed in detail, and a value of k(32) = 10(13.14 +/- 0.55) exp(-17260/T) s(-1) has been obtained over the temperature range 580-783 K. c-C5H9 --> CH2=CHCH2CH2CH2 (32) The cyclisation of C-3, C-4, C-5 and C-6 alken-1-yl radicals has been discussed and it has been concluded that the predominant reaction of hex-5-en-1-yl radicals between 600 and 1300 K and at 1 atm O-2 pressure is cyclisation giving c-hexyl radicals. As the latter rapidly undergo successive oxidation to cyclohexene, cyclohexadiene and then benzene, it has been further concluded that such C-6 cyclisations could be major sources of benzene and substituted benzenes in the oxidation of conventional fuels.