Reação de oxidação do substrato fenólico 2-metoxifenol (Guaiacol) em meio básico, na presença do catalisador mimético zif-67 (DR) e do agente oxidante peroximonossulfato de potássio -oxone®

Abstract

Being the second most abundant natural polymer on the planet, lignin has polyphenolic groups in its structure. These groups make it a promising and economically viable source of aromatic compounds to replace petroleum, the main source of these compounds today. Lignin is found in amounts of 15 to 25% of the herbaceous biomass of plants and represents a large part of the waste generated by industries that use plant matter. Due to its dispersing, binding and emulsifying properties, lignin is commonly used in energy production and in small fractions in other commercial applications. Guaiacol (2 methoxyphenol) is a structural unit of lignin, commonly used as a model compound for this context. The structure of guaiacol can be found in some monomers of lignin molecules, as in the units of coniferyl alcohol (G unit), synapyl alcohol (S unit). For the catalysis of the guaiacol oxidation process, the mimetic catalyst ZIF-67 (DR) can be used, which consists of Co2+ ions coordinated to 4 nitrogen atoms of 2-methylimidazole ligand molecules. ZIF-67 (DR) was first synthesized in 2008 along with a number of other ZIF networks. The present work sought to evaluate the oxidation reaction of the phenolic substrate 2-methoxyphenol (guaiacol) in a basic medium (pH 9), in the presence of the mimetic catalyst ZIF-67 (DR) and the commercial oxidizing agent OXONE® (potassium peroxymonosulfate). By monitoring the activity (U) and specific activity (SA) of the catalyst ZIF-67 (DR) mixed with the oxidizing agent OXONE®, the formation of the tetraguaiacol product was verified, using spectrophotometric measurements in the UV- Vis at 470 nm wavelength. It was possible to visually identify the oxidation of 2-methoxyphenol (guaiacol) and the formation of tetraguaiacol at a wavelength of 470 nm in samples WD007, WD012 and WD013. In samples WD004 and WD005 it was not possible to identify the oxidation of 2-methoxyphenol (guaiacol). In all assays, theoretically low activity (U) and specific activity (SA) results were obtained, with values of 3,5x10-4 for U activity and 1,17x10-3 for specific activity (SA) in the WD013 assay. This is due to the high oxidation power of potassium peroxymonosulfate - OXONE® in mixture with the mimetic catalyst ZIF 67 (DR), making the reaction kinetics very fast, not being able to be detected by the spectrophotometer (UV/VIS) used for the trials of this work. [resumo fornecido pelo autor]