Next-Generation Water-Soluble Homogeneous Catalysts for Conversion of Glycerol to Lactic Acid

Abstract

An attractive method for valorization of glycerol is the catalytic transformation to lactic acid. By overcoming the solubility challenge associated with known homogeneous catalysts for this reaction, we show that thermally robust Ir(I), Ir(III), and Ru(II) N-heterocyclic carbene (NHC) complexes with sulfonate-functionalized wingtips are highly prolific for this process, requiring no cosolvents other than aqueous base. The activity of the catalysts is compared under both conventional heating and microwave conditions. The most active catalyst reaches a TOF of 45 592 h −1 (microwave) and 3477 h −1 (conventional) with 1 equiv of KOH, and proceeds at a constant rate for at least 8 h. Although higher activity is observed with KOH, the catalysts are also highly active with the weaker base, K 2 CO 3 (13 000 h −1 and concurrent formation of formate). The protocol can be modified to achieve quantitative conversion of glycerol in only 3 h. The high activity of these catalysts compared to nonsulfonated analogs is attributed to the stabilization the lactate product in aqueous media. The most active catalyst retains equal activity for crude glycerol. A mechanism is proposed for the most active catalyst precursor involving O−H oxidative addition of glycerol.

Highly Efficient Iridium‐Catalyzed Production of Hydrogen and Lactate from Glycerol: Rapid Hydrogen Evolution by Bimetallic Iridium Catalysts

“…[19] These iridium complexes, including the linear triscarbene ligand, were employed for the catalytic transformation of glycerol to lactate and hydrogen. [20][21][22][23][24][25][26] Because the structural feature of the linear triscarbene ligands can induce multi-metal coordination, it is expected that the cooperative effect of metal ions increases the Figure 1. Examples of tridentate NHC ligands.…”

“…[ 19 ] These iridium complexes, including the linear triscarbene ligand, were employed for the catalytic transformation of glycerol to lactate and hydrogen. [ 20–26 ] Because the structural feature of the linear triscarbene ligands can induce multi‐metal coordination, it is expected that the cooperative effect of metal ions increases the rate of the dehydrogenation of glycerol. Herein, detailed synthetic procedures of these new iridium complexes and catalytic reaction results of hydrogen and lactate generation from glycerol [turnover number (TON); 3,240,000 and turnover frequency (TOF); 162,000 h – 1 ] are presented.…”

Mechanism Analysis and Kinetic Modelling of Cu NPs Catalysed Glycerol Conversion into Lactic Acid

“…Kishida et al [20] found that 90% LA yields could be obtained by the hydrothermal treatment of glycerol at 573 K in the presence of NaOH. The synthesis of LA from glycerol has also been studied in alkaline media in the presence of various water-soluble homogeneous catalytic systems: pincer-type ruthenium complexes [21], thermally robust Ir(I), Ir(III), and Ru(II) N-heterocyclic carbene complexes with sulfonate-functionalized wingtips [22] and others complexes [23,24]. Oxidative conversion of glycerol to LA in an alkaline media in the presence of Pt and Au based catalysts supported on various surfaces proceeds under milder conditions compared to the hydrothermal treatment [25,26].…”

Recent Advances in the Microwave-Assisted Production of Hydroxymethylfurfural by Hydrolysis of Cellulose Derivatives—A Review

“…Using the SiC vessel, the yields of 5-HMF always remained inferior to those obtained with traditional glassware, and the complete transformation using SiC vessels was definitively more energy-consuming (factor 1.7). The difference between the two processes could be remedied by altering the stirring rates to avoid potential hot spots, as illustrated recently in another reaction model [ 51 ].…”