Efficient catalytic hydrogenation of levulinic acid: a key step in biomass conversion

Abstract

γ-Valerolactone (GVL) has been proposed as a sustainable liquid, and could be used for the production of hydrocarbons by using both homogeneous and heterogeneous catalytic systems. The selective reduction of levulinic acid (LA) to GVL is a key transformation for biorefinery concepts based on platform molecules. We report a detailed investigation of the conversion of LA to GVL using molecular hydrogen in the presence of a catalyst in situ generated from Ru(acac) 3 , and electronically and sterically characterized alkyl-bis(m-sulfonated-phenyl)-and dialkyl-(m-sulfonated-phenyl)phosphine (R n P(C 6 H 4 -m-SO 3 Na) 3−n (n = 1 or 2; R = Me, Pr, iPr, Bu, Cp) ligands. The hydrogenation experiments were performed in the range of 5-100 bar H 2 at 140 °C using 0.016 mol% catalyst and 5-20 eqv. of ligand. The effects of hydrogen pressure and Ru/ligand ratio on the LA conversion were determined. The nBuP(C 6 H 4 -m-SO 3 Na) 2 (χ = 12.5, θ Tol = 153°) showed the highest activity achieving turnover numbers up to 6200 with a yield and selectivity higher than 99% in a solvent, chlorine and promoter free reaction mixture. The catalyst was successfully recycled for six consecutive runs without loss of activity. The characterization of sulfonated and non-sulfonated phosphines indicated that the sulfonation had no significant effect on the steric and electronic properties of the ligands.Scheme 1 † Electronic supplementary information (ESI) available. See

Chemical-free Processing of Sweet Sorghum Juice of Cultivar Sucrosorgho 506

“…Among the platform molecules levulinic acid could play a key role in the chain [43], since it is the raw material of a proposed platform chemical (gamma-valerolactone) that can be obtained by its selective hydrogenation [44][45][46][47][48]. Extending the queue a new product, biopolymer generation was established by Tanamool [49] at laboratory scale.…”

An improved catalytic system for the reduction of levulinic acid to γ-valerolactone

“…of tertiary sulfonated phosphines without using any solvent or additive with TOF = 1440-3538 s −1 . 18 It should be noted that this system was also found to be active under continuous conditions. 19 During the decomposition of carbohydrates, LA and formic acid are formed in equimolar amounts.…”

“…For the selective conversion of LA to GVL, the highest activity of the Ru catalyst modified with a monodentate phosphine ligand was achieved by applying Bu-DPPDS under 100 bar H 2 at 140°C (Table 1, entry 2). 18 It was revealed that the hydrogenation activity of the Ru catalysts can be significantly enhanced by the use of chelating-type bidentate Ph 2 P(CH 2 ) n PPh 2 (n = 1-3) ligands. 23 Thus, we compared the activity of a Ru catalyst modified with Ph 2 P(CH 2 ) 4 PPh 2 (Scheme 1, DPPB), a Bu-DPPDS analogue, for the reduction of LA.…”

Homogeneous Catalyzed Reactions of Levulinic Acid: To γ‐Valerolactone and Beyond

“…[41] Sulfonation of these ligands enhances both their solubility in polar solvents and also minimises their vapour pressure making them easier and safer to handle. Catalysts were generated in situ via reaction with Ru(acac) 3 , and catalysis performed at 100 bar H 2 , 140 o C. The steric and electronic properties of the phosphine ligands had significant influence on the activity of the catalysts.…”