Catalytic hydrogenation and hydrogenolysis of lignin model compounds using in-situ, water-soluble Ru/P(CH2OH)(3) systems

Chemical modification of lignin without degradation of its polymeric structure could lower the production cost of higher quality paper, particularly with regard to stabilization toward light-induced yellowing, where the presence of so-called alpha-carbonyls and alpha-hydroxyl groups is of key importance. In order to explore which chromophore groups can be modified, hydrogenation of aromatic lignin model compounds has been tested, using as catalysts in-situ, water-soluble ruthenium species containing tris(hydroxymethyl)phosphine, P(CH2OH)(3). Such systems are active for hydrogenation of activated alkenes, carbonyl groups and, of more interest, hydrogenolysis of some aromatic alcohols. Catalyst activity depends on the phosphine/Ru ratio, the nature of the substrate (particularly substituents of the aromatic ring), and the solvents used. Thus, hydrogenation of a > C=O functionality can give either > CH(OH) or > CH2 depending on the nature of the arene fragment.