Study On The Synthetic Methods Of Pyridylaldehydes,Electron Withdrawing Groups Substituted Benzaldehydes And Phenylacetaldehydes

Pyridylaldehydes, benzaldehydes and phenylacetaldehydes with electron withdrawing groups as synthetic intermediates are of paramount importance and have a huge market with big potential due to their widespread application in the fields of medicine, agriculture, perfumery, food additives, dyes as well as others. Therefore, it is meaningful to develop high-efficient, low-cost and environmentally-friendly synthetic routes that can be employed in industry.After analyzing and summarizing the reported literatures, the methods of gas-phase oxidation in a fixed bed, condensation-oxidation and condensation-hydrolysis which have the advantages of being high-efficient, low cost and environmentally-friendly were designed for the preparation of pyridylaldehydes, benzaldehydes and phenylacetaldehydes with electron withdrawing groups, respectively. The above mentioned methods are simple and easy to practice.When preparing pyridylaldehydes, the gas-phase oxidation of2-picoline to2-pyridylaldehyde was studied over Mo modified V/TiO2catalysts in the first place. The newly prepared V-MO/TiO2catalysts were characterized by XRD, H2-TPR and SEM. The effects of catalyst composition, calcination temperature, reaction temperature, concentration of2-picoline solution and oxygen as well as amount of catalyst were investigated in detail. The research results showed that the addition of Mo to V/TiO2greatly increased reducibility and thus the catalytic activity of the catalysts. Low reaction temperature, high calcination temperature and space velocity led to the high selectivity to2-pyridylaldehyde. The optimal V/Mo molar ratio of the catalyst with7%loading amount was2.9:1. Optimal conditions (calcination temperature=600℃, amount of catalyst=8g, reaction temperature=290℃, flow rate of10%2-picoline solution=0.2mL·min-1, oxygen flow rate=0.1L·min-1) of V-Mo/TiO2catalysts gave70.2%conversion and88.3%selectivity with the reaction rate at1.13mmol·gcat-1·h-1.The novel system of Bi-Mo/TiO2was first applied in the gas-phase oxidation of picolines to pyridylaldehydes. Catalysts were prepared with Bi2Mo3O12(α) and MoO3as active components supported over TiO2, and were characterized by XRD, H2-TPR, NH3-TPD, O2-TPD as well as SEM. The high activity of the Bi-Mo catalysts mainly stemmed from the synergetic effect between Bi2MO3O12(α) and MoO3which was proved and mainly studied. The synergetic effect not only stabilized the crystallographic structure of TiO2and thus maintained the surface area of the catalysts, but also improved the reducible property, oxygen desorption ability and surface acidity of the catalysts, therefore the high catalytic activity. The optimal molar ratio of Bi2Mo3O12(α) to MoO3was1:1. Optimal conditions (calcination temperature=550℃, amount of catalyst=4g, reaction temperature=290℃, flow rate of10%2-picoline solution=0.5mL·min-1, oxygen flow rate=0.1L·min-1) of Bi-Mo/TiO2catalysts gave70.9%conversion and83.1%selectivity with the reaction rate at4.13mmol·gcat-1·h-1. Compared with V-Mo catalysts, Bi-Mo catalysts were much more active.This paper also studied the novel preparation methods of benzaldehydes and phenylacetaldehydes with electron withdrawing groups from toluene derivatives via the two-step condensation-oxidation and condensation-hydrolysis, respectively.In consendation reactions, the usage amount of the reagent DMFDMA and solvent DMF was optimized, good results were achieved and the yields of the products enamines were all over85%.In preparation of benzaldehyde derivatives via oxidation of enamines, the green and cheap oxidant hydrogen peroxide was used, the experiments were carried out under mild conditions and reaction parameters including solvent and its usage amount, the amount of hydrogen peroxide as well as reaction temperature were optimized, and the yields of the products obtained were between50%and70%. When preparing phenylacetaldehydes derivatives, the experiments were also carried out under mild conditions with hydrochloric acid as hydrolyzing agent, and the yields of the product higher than80%, which is promising to be applied in industrial.The structures of the products obtained were verified by1H NMR, MS and GC-MS.