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Solvent Exposure and Toxic Responses
Published in Stephen K. Hall, Joana Chakraborty, Randall J. Ruch, Chemical Exposure and Toxic Responses, 2020
Glycols are hydrocarbons with two hydroxyl groups attached to two adjacent carbon atoms in an aliphatic chain. Glycols are used as antifreezing agents and as solvent carriers and vehicles in a variety of chemical formulations. Only ethylene glycol is in common general industrial use as a solvent, but large volumes of the other glycols are used as vehicles and chemical intermediates. The glycols have such low vapor pressures that inhalation is only of moderate concern unless heated or aerosolized. Ethylene glycol and diethylene glycol are metabolized to glycol aldehyde, glycolic acid, glyoxylic acid, oxalic acid, formic acid, glycine, and carbon dioxide. Oxalic acid is the cause of acute renal failure and metabolic acidosis that occur following ingestion of ethylene glycol. Urinalysis for oxalic acid may be useful in biological monitoring of ethylene glycol exposure. The metabolic pathways of methyl alcohol and ethylene glycol may be competitively blocked by the administration of ethyl alcohol.
Catalytic Oxidations with Air for Clean and Selective Transformations of Polyols
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
Pierre Gallezot*, Michèle Besson, Fabienne Fache
Glyoxylic acid (CHOCOOH) is a useful synthon entering in the preparation of a growing number of fine chemicals. It is prepared industrially by various routes including the oxidation of aqueous solutions of glyoxal (CHOCHO) with nitric acid.5 The oxidation of glyoxal into glyoxylic acid is difficult to achieve selectively because the second aldehyde function is easily oxidized to yield oxalic acid. We have shown previously3 that glyoxal solutions can be oxidized at 40 °C with air in presence of platinum metals supported on active charcoal. Platinum is the most active and selective because its higher redox potential prevents surface poisoning by chemisorbed oxygen. In the present study, the effects of the operating conditions and of the nature of the supports on the selectivity of platinum catalysts have been studied.
Carbon Nanomaterials in Electrolysis and Hydrogen
Published in Shuhui Sun, Xueliang Sun, Zhongwei Chen, Yuyu Liu, David P. Wilkinson, Jiujun Zhang, Carbon Nanomaterials for Electrochemical Energy Technologies, 2017
Yuyu Liu, Hongbing Zhao, Rongzhi Chen, Jinli Qiao, David P. Wilkinson, Jiujun Zhang
Compared with metal electrodes, carbon materials (such as glassy carbon, graphite, carbon black, carbon nanofiber, and carbon tubes) give long-term stability, diverse surface chemistry, and stable bonds of carbon with various surface modifiers [193,194]. Various carbon electrodes without any catalysts, such as glassy carbon, graphite, CNTs, and so on, have been applied to electrochemical CO2 reduction. Christensen and Hamnett [195] reported that CO2 reduction in acetonitrile for glassy carbon electrode was observed only at potentials below −2.2V versus saturated calomel electrode (SCE), and the major product was CO. Under high pressure, the selectivity for reduction products has a close correlation with the applied current density [196]. At a current density of 50 mA cm−2 under 30 atm of CO2, the Faradaic efficiencies were found to be 44% for CO product and 30% for formic acid. With increasing current density, the Faradaic efficiency for CO2 decreased noticeably. Eggins and coworkers [197] investigated the reduction of CO2 on a graphite electrode in pH 9 tetramethylammonium chloride solution. The CO2 was reduced to oxalic acid at −0.9 V (vs. Ag/AgCl) and glyoxylic acid at −1.8 V, and the overall current efficiency was found to be up to 93%.
Biobased polymers from lignocellulosic sources
Published in Green Chemistry Letters and Reviews, 2023
Rachele N. Carafa, Daniel A. Foucher, Guerino G. Sacripante
A study by Manker et al. was able to prepare various biobased polyesters from modified hemicellulose sugars that are biodegradable and have good mechanical properties (34). Birch wood lignocellulose was treated with glyoxylic acid and a strong acid to separate it into its main components via aldehyde-assisted fractionation. The cellulose and lignin were then isolated to leave the hemicellulose portion, particularly the 5-carbon sugar xylose (Figure 9). The reaction between xylose and glyoxylic acid with sulfuric acid produced the diacid precursor diglyoxylic acid (DGAX), which was then refluxed with methanol to form dimethylglyoxylate xylose (DMGX). Polymerization via melt condensation with Lewis acid catalysts of DMGX with various aliphatic diols ranging from C2-C6 formed the desired polyesters, collectively referred to as poly(alkylene xylosediglyoxylates) (PAX) (34).
Ring-opening pathway of 2, 4, 6-trichlorophenol initiated by OH radical: an insight from first principle study
Published in Molecular Physics, 2020
Subrata Paul, Ramesh Chandra Deka, Nand Kishor Gour, Abhishek Singh
Because of poor biodegradability and carcinogenicity of chlorophenols, 2, 4, 6-TCP is among the priority contaminants of major environmental concern. The strong C–Cl bond and the position of Cl atom relative to the hydroxyl group are the main reason for its toxicity and their persistence in the biological environment [22]. It is important to note that due to structural stability, toxicity and persistence, it is difficult to remove from the biological environment. When 2, 4, 6-TCP is heated, it emits corrosive fumes of hydrochloric acid and other toxic gases in the atmosphere. Benitez et al. [23] first performed the experimental study using batch reactor on the kinetics of the decomposition of 2, 4, 6-TCP by ozonation and by Fenton’s reagent reaction and found the rate constant of 5.48 × 109 M−1, s−1 at 25°C for the direct reaction between 2, 4, 6-TCP and hydroxyl radicals (•OH). Further, the decomposition pathway of the ozonation of 2, 4, 6-TCP in aqueous solution was investigated by Yunzheng et al. [24]. They proposed that in the presence or absence of OH• radicals the molecular ozone firstly oxidised 2, 4, 6-TCP to chlorinated quinine, which is subsequently degraded to formic acid and oxalic acid. Mayani et al. [25] further investigated the oxidative degradation of 2-CP, 4-CP, and 2, 4, 6-TCP by Co(II) and Ni(II) impregnated SBA-15 catalyst in an aqueous medium. They reported that in the catalytic oxidation of 2, 4, 6-TCP formed 2, 6-dichloro-1, 4-benzoquinone, maleic acid, fumaric acid, oxalic acid and glyoxylic acid.
Reactions Involved in Phenolics Degradation from Sugarcane Juice Treated by Ozone
Published in Ozone: Science & Engineering, 2019
Juliana A. S. Sartori, Célio F. Figueiredo Angolini, Marcos N. Eberlin, Claudio L. Aguiar
Metabolomics is an emerging technique for prospecting biomarkers and metabolites in agriculture specially to define reaction mechanisms in the agro-industry. MS coupled to liquid chromatography has been able to detect thousands of ions from complex biological samples (Prado et al. 2018). In order to elucidate the mechanisms involved in the degradation of phenolic compounds by ozonation, direct infusion ESI(-)-MS analyzes were performed to try to characterize the molecules present, knowing that main intermediates and final products resulting from phenol ozonation described in the literature are: catechol, hydroquinone, muconic acid, muconic acid aldehyde, maleic acid aldehyde, oxalic acid, glyoxal, glyoxylic acid, formic acid, H2O2 and CO2 and the amount of these products depends on the pH (Mvula and Sonntag 2003; Ramseier and von Gunten 2009).