Development And Application Of High Efficiency Catalyst For 3-Methoxy-4-hydroxymandelic Acid

As well known,vanillin?4-hydroxy-3-methoxybenzaldehyde?is one of the most widely used food spices which can be added to food directly.Furthermore,vanillin was also an important industrial intermediate in pharmaceuticals,fine industry and so on.So,the worldwide demand for vanillin is increasing faster and faster.But,most of the vanillin was produced by chemical oxidation which using a large amount reagent as oxidizing agent in homogeneous system.The homogeneous reaction for vanillin production faced many difficult such as catalysts resume,environmental pollution,high-cost materials of construction and so on.In this context,heterogeneous catalysis in vanillin industry will be helpful for sustainable development.The preparation of vanillin by glyoxylic acid is the most widely used method at home and abroad.Production vanillin by this method has great advantages such as the raw materials were easy to obtained and the brief reaction steps.After the end of the reaction,the yield of vanillin was high and the wastes produced are relatively easy to deal comparative with other method.In this paper,uses and synthetic methods of vanillin were briefly introduced in the first.The technological conditions of preparing vanillin by glyoxylic acid were optimized through the comparison of experimental data.The role of Al3+ in the condensation phase was reasonably explained by in-situ ATR FT-IR and NMR,in the oxidation phase a new catalyst was selected to catalytic oxidation 3-methoxy-4-hydroxy mandelate acid,and the catalytic mechanism was explained.According to the experiment,the higher the ratio of guaiacol,the fewer the by-products will be generated.Considering the recovery cost of guaiacol,the ratio between guaiacol and glyoxylic acid will be controlled at 1.3:1,and the p H value will be controlled at 11.5comprehensively due to the decomposition reaction of glyoxylic acid under alkaline conditions.Through the investigation of the data of reaction time,reaction temperature and amount of aluminum ion,it was finally determined that the reaction temperature should be controlled at 20 ? in the condensation stage for 18 hours and aluminum ion with guaiacol molar amount of 10% was added.Under optimal conditions,the selectivity of the product3-methoxyl-4-hydroxymandelic acid was over 85%,and the selectivity of the by-product2-hydroxy-3-methoxyl-1,5-dimandelic acid was reduced to less than 5%.The 3-methoxyl-4-hydroxymandelic acid was oxidized with a variety of spinel composite metal oxides as catalysts,and the oxidation conditions were optimized to obtain the reaction solution with a p H value of 11,a temperature of 90 ?,a partial oxygen pressureof 0.1 Mpa,and a reaction time of 3 hours to achieve the highest selectivity and yield of vanillin.CuFe₂O₄/SiO₂ and NiCo₂O₄/SiO₂ with better catalytic effects were selected as representatives through comparison of results.The CuFe₂O₄/SiO₂ and NiCo₂O₄/SiO₂ were characterized by XRD,N2 adsorption-desorption,TEM and SEM.The N2adsorption-desorption model indicated that the aggregation of CuFe₂O₄ and NiCo₂O₄ nanoparticles was inhibited after loading SiO₂.At the same time,the influence of different catalyst dosage on the reaction was also investigated.After the dosage of CuFe₂O₄/SiO₂ catalyst was 10% of the mass of 3-methoxyl-4-hydroxymandelic acid,the best catalytic effect could make the conversion rate of 3-methoxyl-4-hydroxymandelic acid and vanillin selectivity reach 98% and 96%,respectively.CuFe₂O₄/SiO₂ in the oxidation system has the advantages of high reaction efficiency,mild reaction conditions and easy recovery,etc.The possible mechanism of CuFe₂O₄/SiO₂ in the oxidation system was studied by in-situ ATR-FTIR and 1H NMR.What's more,decarboxylation takes place under alkaline conditions,not under normal acidic conditions.After NiCo₂O₄/SiO₂ catalyst dosage was 12% of the mass of 3-methoxyl-4-hydroxymandelic acid,the conversion rate and vanillin selectivity of3-methoxyl-4-hydroxymandelic acid reached 98.5% and 96.5%,respectively.Because this kind of catalyst is easy to make and cheap,it is very suitable for the industrial production of vanillin by acetaldehyde method.