title: Role of hydrogen abstraction acetylene addition mechanisms in the formation of chlorinated naphthalenes. 2. Kinetic modeling and the detailed mechanism of ring closure.
abstract: The dominant formation mechanisms of chlorinated phenylacetylenes, naphthalenes, and phenylvinylacetylenes in relatively low pressure and temperature (∼40 Torr and 1000 K) pyrolysis systems are explored. Mechanism elucidation is achieved through a combination of theoretical and experimental techniques, the former employing a novel simplification of kinetic modeling which utilizes rate constants in a probabilistic framework. Contemporary formation schemes of the compounds of interest generally require successive additions of acetylene to phenyl radicals. As such, infrared laser powered homogeneous pyrolyses of dichloro- or trichloroethylene were perturbed with 1,2,4- or 1,2,3-trichlorobenzene. The resulting changes in product identities were compared with the major products expected from conventional pathways, aided by the results of our previous computational work. This analysis suggests that a Bittner-Howard growth mechanism, with a novel amendment to the conventional scheme made just prior to ring closure, describes the major products well. Expected products from a number of other potentially operative channels are shown to be incongruent with experiment, further supporting the role of Bittner-Howard channels as the unique pathway to naphthalene growth. A simple quantitative analysis which performs very well is achieved by considering the reaction scheme as a probability tree, with relative rate constants being cast as branching probabilities. This analysis describes all chlorinated phenylacetylene, naphthalene, and phenylvinylacetylene congeners. The scheme is then tested in a more general system, i.e., not enforcing a hydrogen abstraction/acetylene addition mechanism, by pyrolyzing mixtures of di- and trichloroethylene without the addition of an aromatic precursor. The model indicates that these mechanisms are still likely to be operative.
authors.affiliation: School of Chemical Sciences, University of Auckland , Private Bag 92019, Auckland 1142, New Zealand.
authors.forename: Grant J
authors.initials: GJ
authors.lastname: McIntosh
authors.forename: Douglas K
authors.initials: DK
authors.lastname: Russell
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D002722:Chlorobenzenes / Q000737:chemistry; D003500:Cyclization; D054879:Halogenation; D006859:Hydrogen / Q000737:chemistry*; D007536:Isomerism; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature
chemical_list: D002722:Chlorobenzenes; D009281:Naphthalenes; C036720:trichlorobenzene; C031721:naphthalene; C044736:phenylacetylene; D006859:Hydrogen; D000114:Acetylene