Benzyl alcohol selective oxidation via in-situ generated oxidants

Doctoral thesis English OPEN
Santonastaso, Marco
  • Subject: QD
    mesheuropmc: inorganic chemicals | organic chemicals

Benzyl alcohol oxidation has been carried out through the in situ generation of oxidative species originated from the interaction of an atmosphere of hydrogen and oxygen gases diluted in carbon dioxide, a solution of benzyl alcohol and a catalyst composed of supported gold and palladium nanoparticles.\ud For the selection of the reaction conditions they were taken into account both those used for the direct synthesis of hydrogen peroxide and those used for the benzyl alcohol oxidation. The idea behind this choice was that a compromise is required which could satisfy both the reaction requirements.\ud It has been demonstrated that the reaction proceeds through a radical mechanism, as the addition of quenchers for specific radicals formation suppressed conversion. Optimum conversion and selectivity towards benzaldehyde have been observed when carrying out the reaction with benzyl alcohol using methanol as solvent, as this promotes high hydrogen peroxide synthesis rates and also allows the breaking down of the hydrogen peroxide into oxidative radical species.\ud Testing the benzyl alcohol in situ oxidation in flow conditions has revealed that the benzyl alcohol conversion is inversely proportional to the residence time of the substrate with the fixed catalyst bed, moreover the in situ oxidation reaction has appeared to be limited by the hydrogen mass transfer which by generation of peroxide species increases the substrate conversion up to a maximum value. However, at the same time, the presence of hydrogen in the system may originate side reactions that are in competition with the selective oxidation of benzyl alcohol to benzaldehyde.
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