Radical Pathways of Coal Dissolution in Hydrogen Donor Media. 2. β Scission and 1,2 Aryl Migration Reactions of Radicals Derived from Methylindans and Tetralin at 327-627 deg C

Article abstract of DOI:10.1021/jo01314a005

The 1,2-aryl migration and fragmentation reactions of 1-indanylmethyl (1), 2-tetralyl (2), 2-indanylmethyl (3), 1-tetralyl (4), 2-methyl-1-indanyl (5), and 1-methyl-2-indanyl (6) radicals were studied by flash vacuum pyrolysis of the tert-butyl perester precursors at 327-627 deg C and 10^-2 torr.Radicals 1 and 2 are interconverted via 1,2 aryl migration which is readily reversible at all temperatures.This equilibrium is depleted by β scission of 1 and recyclization to 4 and by β scission of 2 followed by recyclization to 2 or 3 in modest yields.The reverse neophyle-like rearrangement of 2 to 1 occurs with a lower activation barrier than β-scission of 1 to form a 2-(o-vinylphenyl)ethyl radical.Enthalpies, entropies, and free energies of reactions were calculated for the above reactions from group additivity parameters, and activation energies were estimated from values reported for simple alkyl radicals.It is shown that the β scission of 4 and recyclization to 1 is important only at very high temperatures (>500 deg C) as a mechanism for the isomerization of tetralin and related hydroaromatic structures to alkylindans and that the reverse neophyl-like rearrangement of 2 to 1 is the favored pathway for isomerizations observed during dissolution of coal in hydroaromatic media at elevated temperatures.