WO3 suportado em biomassa advinda de quitosana como catalisador para oxidação de sulfetos de alta eficiência

Abstract

CHITOSAN BIOMASS SUPPORTED WO3 AS A CATALYST FOR HIGH EFFICIENCY SULFIDES OXIDATION. Sulfones and Sulfoxides are terrific value compounds, because of their wide applications in pharmaceutical inputs, medicines and agrochemicals. In this work, the selective and efficient oxidation of sulfides into these molecules is presented, using chitosan-derived carbon supported WO3 as a catalyst. The obtained WO3 was acquired through a sustainable coprecipitation process, followed by the fixation of the semiconductor over the carbon acquired through chitosan pyrolysis. Values of 10, 20 and 40% of WO3 over chitosan were evaluated. The obtained composite promotes a more efficient charge separation, due to the interactions between the oxide and the π electrons from the carbon matrix. Structural analysis confirms the obtention of monoclinic WO3 and its interactions with carbon support, while also revealing the acquisition of a nitrogen doped support, achieved through a non-complete deacetylation process through pyrolysis. Among the tested ratios of WO3, the 20 % one (named QT2W) showed the best performance. The optimized conditions were found at 60°C, 120 minutes of reaction, 8 equivalents of H2O2 and 10 mg of catalyst. The solvent used in the process had a crucial part in determining the process selectivity. Acetonitrile and water had the best performance for sulfones obtention, (>98% selectivity) while methanol and ethanol changed the major product obtained to sulfoxides (>71% selectivity). The stability and scaling of the process showed to be best in water, but the ability to oxidize other molecules of interest was found to be in acetonitrile. XPS analysis showed a leaching of the semiconductor that justified the deactivation of the catalyst in acetonitrile. Mechanism tests were conducted and showed the active participation of hydroxyl radical and singlet oxygen, though the use of spectroscopic probes. Other species also had meaningful impact on the process, found though scavenger species test, therefore being able to infer a mechanism of action of the catalyst with active participation of both semiconductor and support. Hence, the work shows the versatility of the catalyst obtained for the oxidation of sulfides to both sulfones and sulfoxides, showing itself as a promising sustainable catalyst for efficient chemical transformations.