Inside Cover: Solvent-Free Catalytic Depolymerization of Cellulose to Water-Soluble Oligosaccharides (ChemSusChem 8/2012)

Several key factors that govern the catalytic conversion of lignin into smaller molecules have been neglected. In the report by Rinaldi et al. on page 1449, some of the many different facets of solvents in the hydrogenolysis of diphenyl ether and, ultimately, of organosolv lignin with Raney nickel are uncovered. Most importantly, solvents are not bystanders in these reactions. The Lewis basicity of solvents very much affects the catalytic activity of Raney nickel, so in nonbasic solvents the catalyst is an extremely active catalyst for hydrogenolysis and hydrogenation, leading then to saturates. In basic solvents, however, Raney nickel is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products. As a result, the conversion of lignin with Raney Ni in methanol results mainly in phenols, even when performed at temperatures as high as 300 °C.