Catalytic Conversion Of Biomass Into Pyrazine Compounds

With the increasing concerns about energy and environmental issues,converting renewable biomass to high value-added chemicals and fuels has attracted great attentions.Pyrazine compounds are important chemical intermediates,which are widely used in pharmaceuticals,spices and food additives production.However,owing to the complexity of pyrazine compounds synthesis processes,the final selectivity and the yield for the product are low.It is highly desirable to develop green method for synthesis of pyrazine compounds.In this study,pyrazine compounds were obtained through the reaction of glycerol derivatives and ammonium containing chemicals.A novel reaction scheme of high value-added pyrazine compounds from glycerol derivatives was established,and green synthesis route to pyrazine compounds was realized.The detailed studies are shown as follows.First,we screened different glycerol derivatives and nitrogen sources.Glycerol-derived 1,3-dihydroxyacetone(DHA)and glyceraldehyde were found to be the most effective precursors,and diammonium phosphate(DPA)is the best nitrogen source for 2-hydroxymethyl-5-methylpyrazine(HMMP)production via ammonization in a one-pot process.The effects of reaction conditions such as reaction solvent,pH value,reactant ratio,reaction temperature and reaction time on the yield of the product were investigated.Under optimal conditions,i.e.,using the mixture solution of dioxane and water at volume ratio of 1:1,90? for 60 min reaction,the HMMP yield reached 72%.The reaction kinetics and apparent activation energy were studied.Correlating to the results of FTIR-ATR and NMR characterizations,a three-step reaction mechanism was proposed,involving ketimine condensation,cyclization,and dehydration reactions.The ketimine condensation is a rapid reaction step,and the cyclization process is a rate determining step for this reaction.Finally,the preparation of 5-methylpyrazine-2-carboxylic acid was attempted by selective catalytic oxidation of HMMP.The selective oxidation of benzyl alcohol was chosen as a model reaction for optimizing of the catalyst,which was then applied to HMMP catalytic oxidation reaction.The results showed that the 0.5%Pd/CeO2 catalyst exhibited the highest activity for benzyl alcohol oxidation.When used to the HMMP catalytic oxidation reaction,25%yield of 5-methylpyrazine-2-carboxylic acid was obtained.