Probing Mechanisms of Aryl–Aryl Bond Cleavages under Flash Vacuum Pyrolysis Conditions
Edward A. Jackson A , Xiang Xue A , Hee Yeon Cho A and Lawrence T. Scott A BA Merkert Chemistry Center, Boston College, Chestnut Hill, MA 02467, USA.
B Corresponding author. Email: lawrence.scott@bc.edu
Australian Journal of Chemistry 67(9) 1279-1287 https://doi.org/10.1071/CH14171
Submitted: 26 March 2014 Accepted: 23 April 2014 Published: 10 June 2014
Abstract
Several biaryls have been subjected to flash vacuum pyrolysis (FVP) at 1100°C and 0.8–0.9 hPa. Product compositions are reported for the FVP of 9-phenylanthracene (1), 2-bromobiphenyl (5), biphenyl (8), 1,10-diphenylanthracene (12), 9-(2-naphthyl)anthracene (17), and 9,9′-bianthracenyl (20). The experimental results have been used to evaluate four possible mechanistic pathways for the cleavage of aryl–aryl bonds under these conditions: (1) the ‘explosion’ of substituted phenyl radicals; (2) hydrogen atom attachment to an ipso-carbon atom of the biaryl followed by C–C bond cleavage; (3) direct homolysis; and (4) loss of a fragment as an aryne. None of these mechanisms by itself successfully accommodates all of the experimental facts. The data suggest that aryl–aryl bond cleavages under FVP conditions involve at least two different mechanistic pathways and that the relative contributions of the competing pathways probably vary from one biaryl to the next.
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