Microwave Flash Pyrolysis: C9H8 Interconversions and Dimerisations

Abstract

The pyrolysis of 2-ethynyltoluene, indene, fluorene, and related compounds has been studied by sealed tube microwave flash pyrolysis (MFP), in concert with modelling of putative mechanistic pathways by density functional theory (DFT) computations. In the MFP technique, samples are admixed with graphite and subjected to intense microwave power (150–300 W) in a quartz reaction tube under a nitrogen atmosphere. The MFP reaction of 2-ethynyltoluene gave mostly indene, the product of a Roger Brown rearrangement (1,2-H shift to a vinylidene) followed by insertion. An additional product was chrysene, the likely result of hydrogen atom loss from indene followed by dimerisation. The intermediacy of dimeric bi-indene structures was supported by pyrolysis of bi-indene and by computational models. Benzo[a]anthracene and benzo[c]phenanthrene are minor products in these reactions. These are shown to arise from pyrolysis of chrysene under the same MFP conditions. MFP reaction of fluorene gave primarily bi-fluorene, bifluorenylidene, and dibenzochrysene, the latter derived from a known Stone–Wales rearrangement.

C9H8 Pyrolysis. o-Tolylacetylene, Indene, 1-Indenyl, and Biindenyls and the Mechanism of Indene Pyrolysis

“…the reversible 1,2-shift of the aryl group, which causes carbon scrambling in a labeled acetylene 5c. This explains the 14 …”

An experimental study of indene pyrolysis with synchrotron vacuum ultraviolet photoionization mass spectrometry

“…[47][48][49] Part of these mass peaks are therefore speculated to be the molecular structures recommended in previous studies. 5,8,12,13,17,30,31,33,35,47,[50][51][52][53][54][55][56] Fig. 7 presents the comparison of six typical PAH groups in both experiments and simulation.…”

“…A few literature studies are related to the detailed chemical kinetics of indene. 6,9,[30][31][32][33][34] Badger and Kimber 9 performed gas chromatography (GC) measurements of indene pyrolysis, and observed a significant amount of benzofluorenes, benz[a]anthracene, benzophenanthrene and chrysene. Laskin and Lifshitz 6 measured thermal decomposition products of indene behind reflected shock waves using a GC.…”

“…Lifshitz et al 34 investigated the pyrolysis of 2-methyl-indene in a shock tube, and partially described the mechanism of indenyl radicals. Flash pyrolysis of indene and 2-ethynyl-toluene (C 2 HC 6 H 4 CH 3 ) was conducted by Ajaz et al, 30 and that of 3-methyl-4-(2 0 -methyl)benzylideneisoxazol-5(4H)-one by Wentrup et al 31 The quantum chemical calculations of Wentrup et al 31 explained the interconversion between indene and 2-ethynyl-toluene by Roger-Brown rearrangement. Measurements of Ajaz et al 30 and Wentrup et al 31 showed that the combination of indenyl or indene could produce large PAHs, such as bi-indenyl and chrysene.…”

Roger F. C. Brown Memorial Issue

“…[30] Richard Johnson (New Hampshire) and his students invented 'microwave flash pyrolysis' and report here on its application in interconversion and dimerisation of C 9 H 8 hydrocarbons (2-ethyltoluene, chrysene and others), including Roger Brown rearrangements. [31] John Brown (Oxford) reports computational studies of the origin of stabilisation of bicyclo[3.2.1]octadienyl anion and related species, [32] and Stephen Glover (Armidale) details studies of the structure, amidicity, and reactivity of N-chlorohydroxamic esters and N-chloro-b,b-dialkylhydrazides, which are anomeric amides with very low resonance energies, i.e. very low degree of the usual stabilisation of amides by delocalization.…”