Radical-induced pyrolysis mechanism in Cal–O and Cal–Cal bond cleavage

Abstract

During direct coal liquefaction, selective Cal–O bond cleavage is critical for phenol production. In this study, anisole and benzyl phenyl ether were chosen as the oxygen-containing model compounds. Radical-induced sites of benzyl phenyl ether were investigated using the Fukui function and energy barrier calculation. The promotion routes of the Cal–O bond cleavage in anisole and benzyl phenyl ether by radicals were illustrated. The formation of o-benzyl phenol was regarded as a sign of benzyl radical-induced pyrolysis based on the most optimal path. The competitive process between the optimal path and β-bond scission path was analyzed from the rate constant perspective. Radical-induced pyrolysis made remarkable differences in product selectivity for benzyl phenyl ether. Similarly, the cleavage of the Cal–Cal bond can also be promoted using two methods of radical induction, which is referred to as a radical chain process. In contrast to benzyl phenyl ethers, the induced pyrolysis of the Cal–Cal bond in bibenzyl is more likely to occur via β-bond scission after the H of CH2 is abstracted by a radical. The findings of this research would provide a theoretical foundation for comprehending the radical mechanism of direct coal liquefaction.