Glycerol to lactic acid conversion by NHC-stabilized iridium nanoparticles

Acceptorless or Transfer Dehydrogenation of Glycerol Catalyzed by Base Metal Salt Cobaltous Chloride - Facile Access to Lactic Acid and Hydrogen or Isopropanol

The dehydrogenation of glycerol to lactic acid (LA) under both acceptorless and transfer dehydrogenation conditions using readily available, inexpensive, environmentally benign and earth-abundant base metal salt CoCl2 is reported here. The CoCl2 (0.5 mol %) catalyzed acceptorless dehydrogenation of glycerol at 160 °C in the presence of 0.75 equiv. of KOH, gave up to 33 % yield of LA in 44 % selectivity apart from hydrogen. Alternatively, with acetone as a sacrificial hydrogen acceptor, the CoCl2 (0.5 mol %) catalyzed dehydrogenation of glycerol at 160 °C in the presence of 1.1 equiv. of NaOt Bu resulted in up to 93 % LA with 96 % selectivity along with another value-added product isopropanol. Labelling studies revealed a modest secondary KIE of 1.68 which points to the involvement of C-H bond activation as a part of the catalytic cycle but not as a part of the rate-determining step. Catalyst poisoning experiments with PPh3 and CS2 are indicative of the homogeneous nature of the reaction mixture involving molecular species that are likely to be in-situ formed octahedral Co(II) as inferred from EPR, HRMS and Evans magnetic moment studies. The net transfer dehydrogenation activity is attributed to exclusive contribution from the alcoholysis step.

Mechanistic Investigations of the Synthesis of Lactic Acid from Glycerol Catalyzed by an Iridium–NHC Complex

In the present work, the reaction pathways and the origin of catalytic activity for the production of lactic acid from glycerol catalyzed by an iridium–heterocyclic carbene (Iridium-NHC) complex at 383.15 K were investigated by DFT study at the M06-D3/6-311++G (d, p)//SDD level. Compared to the noncatalytic reaction pathway, the energy barrier sharply decreased from 75.2 kcal mol−1 to 16.8 kcal mol−1 with the introduction of the iridium–NHC complex. The catalytic reaction pathway catalyzed by the iridium–NHC complex with a coordinated hydroxide included two stages: the dehydrogenation of glycerol to 2,3-dihydroxypropanal, and the subsequent isomerization to lactic acid. Two reaction pathways, including dehydrogenation in terminal and that in C2-H, were studied. It was found that the formation of dihydroxyacetone from the H-removal in C2-H was more favorable, which might have been due to the lower energy of LUMO, whereas dihydroxyacetone could be easily transferred to 2,3-dihydroxypropanal. The analyses of electrostatic potential (ESP), hardness, and f- Fukui function also confirmed that the iridium–NHC complex acted as a hydrogen anion receptor and nucleophilic reaction center to highly promote the conversion of glycerol to lactic acid.

A review of recent developments on kinetics parameters for glycerol electrochemical conversion - A by-product of biodiesel

Glycerol is a by-product produced from biodiesel, fatty acid, soap and bioethanol industries. Today, the value of glycerol is decreasing in the global market due to glycerol surplus, which primarily resulted from the speedy expansion of biodiesel producers around the world. Numerous studies have proposed ways of managing and treating glycerol, as well as converting it into value-added compounds. The electrochemical conversion method is preferred for this transformation due to its simplicity and hence, it is discussed in detail. Additionally, the factors that could affect the process mechanisms and products distribution in the electrochemical process, including electrodes materials, pH of electrolyte, applied potential, current density, temperature and additives are also thoroughly explained. Value-added compounds that can be produced from the electrochemical conversion of glycerol include glyceraldehyde, dihydroxyacetone, glycolic acid, glyceric acid, lactic acid, 1,2-propanediol, 1,3-propanediol, tartronic acid and mesoxalic acid. These compounds are found to have broad applications in cosmetics, pharmaceutical, food and polymer industries are also described. This review will be devoted to a comprehensive overview of the current scenario in the glycerol electrochemical conversion, the factors affecting the mechanism pathways, reaction rates, product selectivity and yield. Possible outcomes obtained from the process and their benefits to the industries are discussed. The utilization of solid acid catalysts as additives for future studies is also suggested.

Selective and high yield transformation of glycerol to lactic acid using NNN pincer ruthenium catalysts

A sterically less hindered 2,6-bis(benzimidazol-2-yl)pyridine based pincer–ruthenium complex has been used here to accomplish the catalytic conversion of glycerol selectively to lactic acid in high yield.