Wood Eye! Selective Aerobic Oxidation of C-C Bonds in Lignin Models and Extracts using Base Metal Complexes: A Comparison of Oxovanadium and Copper Catalysts
Selective aerobic oxidation of lignin is being explored with a view to obtaining valuable aromatic chemicals. While many C-O bonds can be cleaved by heat or acid treatments to afford aromatic products such as vanillin, selective oxidative cleavage of C-C bonds may afford complementary aldehyde and acid products that could be converted subsequently into value-added aromatic chemicals. In previous work we showed that pyridine enables a novel 2 e- alcohol oxidation mechanism using oxovanadium complex catalysts and air.
This led to different selectivity in C-C bond cleavage reactions of diols and a-hydroxyether lignin models vs. less basic solvents such as acetonitrile or DMSO. In contrast, use of simple copper halide salts in pyridine  bypasses the C-H oxidation pathway in favour of direct C-C bond cleavage. Reactivity of the copper and vanadium catalysts in the oxidation of more complex b-O-4 lignin model compounds and tree-derived lignin extracts will be compared and the differences in selectivity discussed.
 Zakzeski, J.; Bruijnincx, P. C. A.; Jongerius, A. L.; Weckhuysen, B. M. Chem. Rev. 2010, 110, 3552- 3599. See also Canada’s Lignoworks research network: http://www.lignoworks.ca/.
 (a) Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L.; Sutton, A. D.; Thorn, D. L. J. Am. Chem. Soc. 2009, 131, 428-429. (b) Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L.; Silks, L. A.; Thorn, D. L., J. Am. Chem. Soc. 2010, 132, 17804–17816.
 Hanson, S. K.; Baker, R. T.; Gordon, J. C.; Scott, B. L., Thorn, D. L. Inorg. Chem. 2010, 49, 5611-5618.
 (a) Lanfranchi, M.; Prati, L.; Rossi, M.; Tiripicchio, A. J. Chem. Soc., Chem. Commun. 1993, 1698-1699; (b) Prati, L.; Rossi, M. J. Mol. Catal. A 1996, 110, 221-226.
 Sedai, B.; Díaz-Urrutia, C.; Baker, R. T.; Wu, R.; Silks, III, L. A.; Hanson, S. K. ACS Catalysis, 2011, 1, 794-804.