Aqueous organic chemistry. 8. Reactivity of biaryls

Biphenyl, or more accurately biaryl, linkages represent the most refractory cross-links in fossil fuel resources. They are essentially unreactive thermally and in supercritical water at 460 °C. Many biaryls do, however, undergo bond cleavage and heteroatom removal under reducing conditions in supercritical water. 2-Arylpyridines, -quinolines, and -indoles are most reactive in 15% aqueous formic acid whereas the corresponding 2-arylthiophene and -benzothiophene derivatives are more reactive in 15% aqueous sodium formate. Major hydrocarbon products are benzene and naphthalene and their C 1 -C 4 alkylated derivatives. In most cases where conversion is not quantitative after 1 h at 460 °C, the product slate consists of hydrogenated and cleaved products which, given more reaction time, are on the pathway toward complete heteroatom removal.