A Shock Tube Study of H Atom Addition to Cyclopentene

Abstract

We report shock tube studies of the kinetics of H atom addition to cyclopentene and modeling of the subsequent decomposition of cyclopentyl. Hydrogen atoms were generated with thermal precursors in dilute mixtures of cyclopentene and a reference compound in argon. Addition of H to the double bond leads to a cyclopentyl radical that rapidly ring opens and decomposes to ethene and allyl radical. The process was monitored by postshock gas chromatographic analysis of ethene and rate constants determined relative to H atom displacement of methyl from 1,3,5‐trimethylbenzene (135TMB). At 863–1167 K and 160–370 kPa, we find trueleftk()normalH+ cyclopentene → ethene + allyl /k()normalH+135 TMB →m‐xylene+ CH 3left1em=10−0.196prefixexp()19950.28emnormalK/italicT and, with kH+135 TMB →m‐xylene+ methyl =6.70×1013exp−3255K/T cm 3 mol −1s−1, we obtain truerightk()normalH+ cyclopentene → ethene + allyl =4.27×1013prefixexp()−12600.16emnormalK/italicT0.28em cm 30.28em mol −10.28emnormals−1 Using experimental values of about 3:1 for the ratio of C─C to C─H beta scission in cyclopentyl radicals and a corresponding transition‐state‐theory/Rice‐Ramsberger‐Kassel‐Marcus (TST/RRKM) model, the high‐pressure rate expression for addition of H to cyclopentene at 863–1167 K is derived as truerightk∞()normalH+ cyclopentene → cyclopentyl =5.37×1013prefixexp()−12130.28emnormalK/italicT0.28em cm 3 mol −1normals−1 Combined with literature results from lower temperatures and a fitted TST model, the rate expression between 298 and 2000 K is determined as truerightk∞()normalH+ cyclopentene → cyclopentyl =9.1×107italicT1.78prefixexp()−3240.16emnormalK/italicT cm 30.28em mol −10.28emnormals−1 Results are compared with related systems. Near 1000 K, our data require a minimum value of 1.5 for branching between beta C─C and C─H scission in cyclopentyl radicals to maintain established trends in H addition rates. This conflicts with current computed values and those used in existing kinetics models of cyclopentane combustion. We additionally report and discuss minor observed channels in the decomposition of cyclopentene, including formation of 1,4‐pentadiene, (E/Z)‐1,3‐pentadiene, 1,3‐butadiene, and the direct elimination of H2 from cyclopentene to give cyclopentadiene.

Kinetics of isopropanol decomposition and reaction with H atoms from shock tube experiments and rate constant optimization using the method of uncertainty minimization using polynomial chaos expansions (MUM‐PCE)

“…Rate constants involving the H precursors were likewise held constant. C 2 H 5 I chemistry has been extensively studied, 60,63,94–97 and we adopted the mechanism and rate constants from the detailed review of Bentz et al 60 HME decomposition has been frequently used at NIST for production of H atoms 53,65,98 . Tsang 52 has reported rate constants that are linked to standard reference reactions 46,55,58 and should be reliable.…”

“…C 2 H 5 I chemistry has been extensively studied, 60,63,[94][95][96][97] and we adopted the mechanism and rate constants from the detailed review of Bentz et al 60 HME decomposition has been frequently used at NIST for production of H atoms. 53,65,98 Tsang 52 has reported rate constants that are linked to standard reference reactions 46,55,58 and should be reliable. In the present work, the minor channel-producing propene from HME (R1543) impacts results under some of our conditions.…”

Experimental and kinetic modeling study of the oxidation of cyclopentane and methylcyclopentane at atmospheric pressure

“…Figure 3 illustrates a comparison of the different branching ratios; in this figure, R2 and R3, calculated at 1 atm, were gathered in order to compare with the C H and the C C β-scission routes. As can be seen from this figure, for Tsang 34 and Sirjean et al 11 the C H βscission pathway involving the formation of cyclopentene dominates over the temperature range of interest while for Manion and Awan 35 and for Sun et al 36 the C C β-scission channel (R2+R3) dominates. Intermediately, Al-Rashidi et al 5 calculated a crossover temperature (ca.…”

“…The decomposition reactions by β-scission of the primary radicals of both fuels were also considered. β-Scission reactions involved in the consumption of cyclopentyl radicals were studied by several authors 5,11,34,35 with significantly different results in terms of branching ratios. For most of these authors, two pathways are considered: (i) the C H β-scission yielding cyclopentene from cyclopentyl (reaction R1) and (ii) the ring opening (C C β-scission) of cyclopentyl yielding pent-1-en-5-yl (reaction R2).…”

Exploring the combustion chemistry of a novel lignocellulose-derived biofuel: cyclopentanol. Part I: quantum chemistry calculation and kinetic modeling

“…Recently, Al Rashidi et al [29] calculated the high-pressure limit rate constants of this reaction together with the C-H β-scission of cyclopentyl radicals at a high level of theory and determined subsequently the pressure-dependent rate constants based on the fall-off parameters from [30]. While Manion and Awan [43] reported that the C-C/C-H branching ratio of cyclopentyl radicals predicted by these rate constants [29] is still different from their experimental observation, these most recently calculated pressure-dependent rate coefficients are taken in the mechanism for the C-C and C-H β-scission reactions of hydroxycyclopentyl radicals.…”