Isomerization and Decomposition Reactions in the Pyrolysis of Branched Hydrocarbons: 4-Methyl-1-pentyl Radical

Abstract

The kinetics of the decomposition of 4-methyl-1-pentyl radicals have been studied from 927-1068 K at pressures of 1.78-2.44 bar using a single pulse shock tube with product analysis. The reactant radicals were formed from the thermal C-I bond fission of 1-iodo-4-methylpentane, and a radical inhibitor was used to prevent interference from bimolecular reactions. 4-Methyl-1-pentyl radicals undergo competing decomposition and isomerization reactions via beta-bond scission and 1, x-hydrogen migrations (x = 4, 5), respectively, to form short-chain radicals and alkenes. Major alkene products, in decreasing order of concentration, were propene, ethene, isobutene, and 1-pentene. The observed products are used to validate a RRKM/master equation (ME) chemical kinetics model of the pyrolysis. The presence of the branched methyl moiety has a significant impact on the observed reaction rates relative to analogous reaction rates in straight-chain radical systems. Systems that result in the formation of substituted radical or alkene products are found to be faster than reactions that form primary radical and alkene species. Pressure-dependent reaction rate constants from the RRKM/ME analysis are provided for all four H-transfer isomers at 500-1900 K and 0.1-1000 bar pressure for all of the decomposition and isomerization reactions in this system.

A detailed chemical kinetic modeling and experimental investigation of the low‐ and high‐temperature chemistry of n‐butylcyclohexane

“…These rate constants are pressure‐dependent, nine‐parameter (Troe) fits. Based on the notes in JetSurf 2.0, these rate constants are based on acyclic rate constants from published work and from work‐in‐progress of Tsang and co‐workers 29 . For alkyl radical isomerization (Reaction Class 4), the rate constants used were generally estimated by Sirjean and Wang for nBCH as in JetSurf 2.0.…”

“…Based on the notes in JetSurf 2.0, these rate constants are based on acyclic rate constants from published work and from work-in-progress of Tsang and co-workers. 29 For alkyl radical isomerization (Reaction Class 4), the rate constants used were generally estimated by Sirjean and Wang for nBCH as in JetSurf 2.0. For the isomerizations on the alkyl group only, the rates are from Sarathy et al 28 Concerning the chemistry of the cyclic alkenes formed from nBCH, all the n-butylcyclohexene isomers are included.…”

Shock Tube and Kinetic Modeling Study of Cyclopentane and Methylcyclopentane

“…It is noted that the rate constant of R52 is multiplied with 2 to consider two C−C bond cleavages yielding 2-methylpent-5-yl. In addition, the rate constant of 2-methylpentyl (CH 3 -2-P5XC 5 H 10 ) forming methyl and npentene, given by McGivern et al 47 was adopted to CH 3 S2XcC 5 H 8 yielding cyclopentene plus methyl (R55). These analogy approaches are also used in ring opening reaction for MCH in JetSurF2.0.…”

Kinetics of 1,6-hydrogen migration in alkyl radical reaction class

“…This is because direct measurements of the rate constants of decomposition are difficult due to the competition between the multichannel reactions with short lived and highly reactive intermediates. A series of shock tube results with a quoted uncertainty of less than a factor of 2, for both n-alkyl and branched alkyl radicals, were reported by Tsang and co-workers [11][12][13]. The authors presented high pressure limits of rate constants for all possible H migrations and C-C bond beta scissions of the n-hexyl, n-octyl and 4-methyl-1-pentyl radicals.…”