Alain Trichet

Reaction pathways of glucose oxidation by ozone under acidic conditions

The ozonation of d-glucose-1-(13)C, 2-(13)C, and 6-(13)C was carried out at pH 2.5 in a semi-batch reactor at room temperature. The products present in the liquid phase were analyzed by GC-MS, HPAEC-PAD, and (13)C NMR spectroscopy. Common oxidation products of glucose have also been submitted to identical ozonation conditions. For the first time, a pentaric acid was identified and its formation quantitatively correlated to the loss of C-6 of glucose in the form of carbon dioxide. Potential mechanisms for the formation of this pentaric acid are discussed. The well-accepted pathway involving the anomeric position in glucose, gluconic acid, arabinose, and carbon dioxide is reinvestigated. The origin of small molecules such as tartaric, erythronic, and oxalic acids is clarified. Finally, new reaction pathways and tentative mechanisms consistent with the formation of ketoaldonic acids and smaller acids are proposed.

Degradation of cellulose models during an ozone treatment. Ozonation of glucose and cellobiose with oxygen or nitrogen as carrier gas at different pH

Abstract Many parameters can influence the kinetics of cellulose models ozonation. In this work the effect of pH and oxygen as gas carrier on the evolution of the reaction was studied. The involvement of free radical species seemed to be unimportant in high ozone concentration available in water, even at high pH with regard to the reaction rate and by-product formation. Conversely, in basic pH conditions better reaction selectivity with formation in a higher yield of gluconic acid and cellobionic acid was found during the glucose and the cellobiose ozonation. The participation of the solvent and the partial ionization of the hydroxyl group at the Cl position explain this enhanced selectivity. Furthermore, the formation of compounds with a low molecular weight has been proved to be due to a hydrotrioxide fragmentation mechanism involving oxygen.

Origin and significance of the production of carbon dioxide during the ozonization of 13C-labeled d-glucose at different pH values☆

[1-(13)C], [2-(13)C] and [6-(13)C] D-glucose were, respectively, ozonized in a semi-batch reactor in acidic and basic conditions. The composition of the gas phase was evaluated by on-line mass spectrometry measurements. The quantitative and isotopic analyses of the carbon dioxide formed during ozonization are presented and discussed. The data, correlated with previous literature results, clearly show that at pH 2.5 the production of carbon dioxide from C-6 and C-1 carbon atoms is nearly equivalent. Conversely, at higher pH values, CO(2) is released with a greater selectivity from the reducing end. The importance of the decarboxylation reaction in the formation of by-products with fewer than six carbon atoms is also demonstrated.

Fluorescent Brightener 28 Removal by Ozonation or Advanced Oxidation Processes (O3/H2O2)

Abstract The aim of this work is to study the reaction of ozone and combined ozone/hydrogen peroxide mixtures with the fluorescent brightener 28 in dilute aqueous solution using controlled experimental conditions. The kinetics were also evaluated under various experimental conditions. The main ozonation by-products have been identified by High Pressure Anionic Exchange Chromatography (HPAEC) and Gas Chromatography coupled with Mass Spectrometry (GC-MS) techniques and a reaction pathway is proposed. In order to confirm this mechanism, melamine and s-triazine have been treated under the same reaction conditions and their decomposition pathways were studied.

Ozonation Reactions of Monomer and Dimer Lignin Models: Influence of a Catalytic Amount of a Manganese Cyclam Derivative on the Ozonation Reaction

Abstract This work focuses on the study of the reactivity of ozone with lignin models such as vanillin and dehydro-di-isoeugenol (DHDIE) in methanol solution. The primary by-products formed are characterized by Gas Chromatography - Mass Spectrometry (GC-MS) and possible mechanisms for the formation of these by-products are suggested. In the presence of a catalytic amount of a manganese tetraazamacrocyclic complex, other degradation derivatives are identified during DHDIE ozonation, proving that the complex induces a different reactivity of ozone towards the model.

Experimental and theoretical study of stereoelectronic and H-bond control of reactivity in α- and β-methyl d-glucopyranoside ozonolysis

Abstract The topography of the molecular electrostatic potential (MEP) of α and β anomers of methyl d -glucopyranosides has been used to analyze the reactivity of these species towards electrophilic attack and to complete the results we obtained during the ozonation reaction. Molecular mechanics (MM) and molecular dynamics (MD) simulations have been performed to screen the conformational space of α- and β-methyl d -glucopyranosides in order to determine the chair conformations which correspond to a global minimum energy conformation. Density Functional Theory (DFT) (Faststructure) and PM3 (semiempirical) calculations have been carried out to refine the geometries of the 4 C 1 and 1 C 4 chair conformations of both anomers. The MEPs of the α and β anomers in their 4 C 1 chair conformations have been determined by DFT calculations and have been used to predict their respective reactivities. The good agreement between predicted and experimental results observed in organic solutions compared with those performed in aqueous solutions indicates that the water molecules play an “active” role in modifying the intramolecular H-bonds which control the MEP topography and consequently the chemical reactivity of both anomers in solutions.