Cleavage of biphenyl moieties: An efficient new reaction pathway in catalytic hydrocracking

Abstract

The hydrocracking of the five-carbon-membered-ring-containing PNA fluoranthsene (I) is qualitatively different from the classical pattern. A major reaction pathway involves hydrogenation to give tetrahydrofluoranthene (II), center ring opening to give phenyl tetralin (III), and biphenyl cleavage to give tetralin (IV) and benzene. This mechanism includes protonation of (III) followed by an internal 1,5-hydride shift to afford the carbenium ion III{sup +}, of III, represented in the benzylic form. A 1,3-hydride shift of a resonance form of III{sup +} affords benzene and a carbenium ion IV{sup +}, the deprotonation of which leads to an intermediate, dialin, which is rapidly hydrogenated to yield tetralin. The noteworthy reaction in the sequence, which is a net 1.5-shift of the benzylic hydride to the ring bearing the positively charged carbon, evidently takes place along a molecular topology that includes a strong biphenyl linkage. This suggests an apparent structural moiety for efficient cleavage of strong biphenyl linkages, which otherwise would require prior hydrogenation. Thus, the authors have investigated the catalytic hydrocracking of molecules that either contain this structural moiety, or can react to form it. Experiments were done to determine the hydrocracking pathways and kinetics of 9-ethyl fluorene, 9-phenyl anthracene, and 2-phenyl naphthalene in the presencemore » of an equilibrated Ni-Mo/Al{sub 2}O{sub 3}-catalyst-containing ultra-stable Y-Zeolite at 310-380 C and 153 atm.« less