Non-food based biomass (lignocellulose) is an attractive renewable carbon feedstock for the production of chemicals or fuels. Lignin, a key constituent (15À30%) of lignocellulose, is an irregular polymer composed of methoxy-substituted phenyl and phenolic subunits. 1,2 Because of its structural complexity and inherent resistance to chemical reactivity, lignin has been considered a major obstacle in the production of biofuels from lignocellulose.Recently, increasing attention has been focused on the development of methods to convert lignin into more valuable and useful products. 3,4 Reductive approaches using hydrogen or formic acid have been developed to transform lignin into mixtures of monomeric phenols and alkanes suitable for use as fuel additives. 5À9 Catalytic oxidation of lignin using environmentally friendly oxidants (O 2 , H 2 O 2 ) has also been explored as a means to break lignin down into monomeric products. 10À15 Crestini, Chen, Dolphin, and others have investigated the oxidation of lignin and lignin model compounds using H 2 O 2 and transition metal catalysts, including Mn and Fe complexes of porphyrin and TACN ligands (TACN = triazacyclononane). 16À21 While the reduction of lignin is well suited for the production of fuels, aerobic oxidation is advantageous in that it requires no added reagents and could preserve a high degree of the functionality present in the original lignin polymer.Oxidation is also the primary pathway by which lignin is broken down in nature. Both the enzymes lignin peroxidase and manganese-dependent peroxidase are thought to mediate the oxidative disassembly of lignin by wood-rotting fungi. 22À24 To establish the mechanisms of these enzymes, detailed studies have been carried out of the oxidation of arylglycerol β-aryl ether compounds, 25À28 which are models for the lignin β-O-4 linkage, a predominant structural feature representing approximately 50% of the linkages occurring in the natural polymer. 29 For example, oxidation of lignin model compound 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)propane-1,3-diol (1) (Scheme 1) by lignin peroxidase affords products resulting from cleavage of the

The reactivity of homogeneous oxovanadium and copper catalysts toward aerobic oxidation of phenolic and nonphenolic β-1 lignin model compounds has been investigated. Aerobic oxidation of diastereomeric, nonphenolic β-1 lignin models (1T, 1E) using the sixcoordinate vanadium complex (HQ) 2 V V (O)(O i Pr) (HQ = 8-oxyquinolinate) as a precatalyst in pyridine afforded ketone (3) and dehydrated ketone (4) derived from oxidation of the secondary alcohol. In contrast, using CuOTf/2,6-lutidine/TEMPO (OTf = trifluoromethanesulfonate, TEMPO = 2,2,6,6-tetramethyl-piperidin-1-yl-oxyl) in toluene for the same reaction afforded 3,5dimethoxybenzaldehyde ( 5) and 4-methoxybenzaldehyde (6) as major products resulting from C α −C β bond cleavage. Reactions of the corresponding phenolic lignin model compounds (2T, 2E) with 10 mol % CuOTf/2,6lutidine/TEMPO gave ketone (9) as the major product, whereas 10 mol % (HQ) 2 V V (O)(O i Pr) or a stoichiometric amount of CuOTf/2,6-lutidine/TEMPO yielded 2,6-dimethoxybenzoquinone (10) as the major product, arising from cleavage of the C aryl − C α bond. Different selectivity was observed in the oxidation of 2T, 2E using the five-coordinate complex (dipic)V V (O)(O i Pr) (dipic = dipicolinate), with α,β-unsaturated aldehyde ( 14) as the major product (formed from oxidation of the primary alcohol and dehydration). The key differences in chemoselectivity between the vanadium and copper catalysts in the oxidations of these phenolic and nonphenolic β-1 lignin models are discussed.

Direct methane functionalization to value-added products remains a challenge because of the propensity for overoxidation in many reaction environments. Sulfonation has emerged as an attractive approach for achieving the necessary selectivity. Here, we report a practical process for the production of methanesulfonic acid (MSA) from only two reactants: methane and sulfur trioxide. We have achieved >99% selectivity and yield of MSA. The electrophilic initiator based on a sulfonyl peroxide derivative is protonated under superacidic conditions, producing a highly electrophilic oxygen atom capable of activating a C–H bond of methane. Mechanistic studies support the formation of CH3+as a key intermediate. This method is readily scalable with reactors connected in series for prospective production of up to 20 metric tons per year of MSA.

Lignin is a unique potential source of aromatic chemicals derived from renewable resources.Homogeneous oxovanadium, copper and cobalt complexes exhibit intriguing selectivity for the aerobic oxidation of complex lignin models, affording some control of C-C, C-H and C-O bond cleavage. In this work these catalysts are compared, along with a metal-free variant, for their performance in oxidation and depolymerisation of organosolv lignin, as determined by gel permeation chromatography (GPC), quantitative-heteronuclear single quantum correlation (q-HSQC) and 31 P NMR spectroscopy of derived phosphite esters. Although most catalysts oxidized the lignin extracts, the oxovanadium(V) complexes, [VO(O i Pr)L n ] (L n ¼ dipic or (HQ) 2 where dipic ¼ dipicolinate and HQ ¼ 8-oxyquinoline) demonstrated the highest degree of lignin depolymerisation. Further ligand development is achieved with a tethered base (pyridine) in the novel BPAMP(V V )(O)(O i Pr) catalyst [H 2 PAMP ¼ N,N-bis(3,5-di-tertbutyl-2-phenol)-N-(methylpyridine)amine]. Efficient oxidation and some degree of depolymerisation is achieved with this new bifunctional catalyst without the addition of exogenous base.