Study On Synthesis Of Allantion Catalyzed By Solid-superacid

Allantoin has accelerated cell growth,promoted wound healing,softening keratin and other properties,which was widely used in medicine,light industry,agriculture,daily chemical and other fields.Therefore,allantoin market demand increased year by year.Up to now, the methods for preparing allantoin still involve homogeneous protonic acid used as catalysts via the condensation and cyclization of glyoxylic acid and urea in industry. However, high dosage and non-regeneration of catalysts and the large three wastes were the disadvantages of catalyst.It was of great significance for researching the clean,green, reusable catalyst. The solid superacid was most actively pursued in the acidic catalyst. In order for the theoretical foundation in the catalytic process of SO42-/MxOy solid superacid as catalyst, in the paper,the allantion was studied in the catalytic action of SO42-/MxOy solid superacid,produced in the way of the condensation and cyclization of glyoxylic acid and urea.The common form of SO4-/MxOy solid superacid were SO42-/TiO2,SO42-/Fe2O3, SO42-/ZrO2 and SO42-/SnO2.In order to increase the conversion rate of the reaction,it was significant of finding the solid superacid,which was the most catalytic action of these four ones and whose method aws used. After the impregnation and activation of treatment, the solid superacid were used as a catalyst in the reaction of glyoxylic acid and urea.In this way,the paper investigated the impact of the carrier and the preparation method on the reaction conversion rate.The solid superacid were characterized. The results showed as follows:When the catalyst is SO42-/TiO2, strong surface acidity and the conversion rate was better;S042-/TiO2 which was got by Low temperature method had more dispersed particles,much bigger surface area,better thermal stability, more acidic, higher activity and better storage stability.Therefore, TiO2 was chosen as the carrier and the solid superacid was produced by low temperature method.When TiO2 was chosen as the carrier and the solid superacid was produced by low temperature method,the structure and surface acidity of SO42-/TiO2 were doped by different metal elements and modificated with several promoter.The solid superacid was considered from the surface acidity, catalytic activity and stability. The solid superacid were characterized. The results showed that their structure was improved,their surface acidity was stronger and their catalytic activity was better after the doping of metal elements;when ammonium persulfate was as the promoter,their particles were thinner, their surface acidity was stronger and their catalytic activity was improved;this catalyst modificated became better stability and their catalytic activity were recoverd after the simple treatment of the impregnation and calcination.SO42-/TiO2 modificated was as a catalyst in the reaction of the condensation and cyclization of glyoxylic acid and urea.The optimal process conditions were explored in the orthogonal and single factor experiments. The results showed that when the molar ratio of glyoxylic acid and urea,the reaction temperature was 75℃,the most appropriate inputs of the catalyst was 4%(the mass ratio of catalyst and glyoxylate), tetrahydrofuran was as the solvent, ethylene dichloride was as the water,the.conversion rate was up to 71.49%; the yield of allantoin catalyzed by the solid superacid modificated was more 16.56% than one without the modified treatment.It was considered the mechanism of the reaction of glyoxylic acid and urea catalyzed by SO42-/MxOy.Their reaction was that the carbonyl carbon of glyoxylate attacked urea which was as the nucleophile.The Bronsted acid on the surface of SO42-/MxOy could accelerate the transfer of H+ between the reactants. The Lewis acid on the surface of SO42-/MxOy could enhance the electropositive of the carbonyl carbon of glyoxylate,which increased the offensive capability of nucleophile.