Coal Liquefaction Model Studies: Radical-Initiated and Phenol-Inhibited Decomposition of 1,3-Diphenylpropane, Dibenzyl Ether, and Phenethyl Phenyl Ether

Article abstract of DOI:10.1021/jo00175a002

The thermal decompositions of 1,3-diphenylpropane (1), dibenzyl ether (2), and phenethyl phenyl ether (3) have been studied in the temperature range of 138-250 deg C in the presence of various free-radical initiators.Thermodynamic calculations of the conversion of 1 to toluene and styrene indicate the reaction is unfavorable below 300 deg C, and 1 was found to be unreactive with di-tert-butyl peroxide (TPO) at 138 deg C, di-tert-butyldiazene (TBD) at 200 deg C, and 1,1,2,2-tetraphenylethane (TPE) at 250 deg C.Reactions of 2 to toluene and benzaldehyde and of 3 to phenol and styrene were calculated to be energetically favorable at these temperatures. 2 reacted in the presence of TPO, TBD, and TPE to give toluene, benzaldehyde, and 1,2-diphenylethane in a free-radical chain process. 3 reacted in the presence of TBD and TPE to give phenol and styrene but did not react with TPO.Reaction of 2 can be inhibited with 2,6-di-tert-butyl-4-methylphenol.With TPO as the initiator the reaction was -0.61 order in phenol, while with TBD as the initiator the reaction was -1.1 order in phenol.The change in reaction order is due to changes in the rates of the various hydrogen-transfer reactions.The hindered phenol did not inhibit reaction of 2 at temperatures above 200 deg C.The mechanisms of these reactions and the implications for coal liquefaction processes are discussed.