Research And Application Of Transfer Hydrogenation

Transfer hydrogenation is a kind of organic reaction in which reduction proceeds by transfering hydrogen atoms from the hydrogen donor to the unsaturated group, it is usually performed in benign condition. The hydrogen donor includes alcohols, hydrocarbons, amines, formic acid, formates, et al. The oxidized hydrogen donors, including aldehyde, ketone, alkene and inorganic molecues, in which the organic molecules are valuable and can be recycled. Application of transfer hydrogenation is attracting more and more attention as it is clean and environmentally benign. Many unsaturated groups, such as nitro, imine, carbonyl, azo, alkene, et al, can be reduced via transfer hydrogenation. However, transfer hydrogenation of some other groups, such as sulfonyl, cyano, et al, has not been fully investigated, especially that cheap hydrogen donors have not been employed in the reduction of the above groups. My work mainly focused on the application of cheap hydrogen donors in the hydrogenation of sulfonyl and cyano, application of transfer hydrogenation in the synthesis of other nitrogen-containing compounds was also investigated. The main points in this thesis are as follows:Transfer hydrogenation of aryl sulfonic compounds. Uncatalyzed transfer hydrogenation of aryl sulfonic amine and aryl sulfonic chloride using formates as hydrogen donor was investigated, and the reactions were carried out at150～200℃with yields of thiophenols between50%and90%. Catalyzed transfer hydrogenation of aryl sulfonic acid and aryl sulfonic chloride was investigated. For the reduction of aryl sulfonic acid, PPh3-Pd/C-iodine was used as catalyst, and isopropanol was used as hydrogen donor and solvent. Thiophenols were obtained at reflux with yield of80～90%. While for the reduction of aryl sulfonic chloride, PPh3-Pd/C was used as catalyst, and formic acid was used as hydrogen donor and solvent. Thiophenols were obtained at80℃with yield of80～90%. Aryl disulfide could also be reduced in the system which employed PPh3-Pd/C as catalyst and formic acid as hydrogen donor. The reaction temperature was80℃, and the yield of corresponding thiophenol is about90%.Transfer hydrogenation of cyano. Transfer hydrogenation of cyano was performed in DBU based ionic liquids with Raney Ni as catalyst, and the temperature was70℃. The yields of corresponding amines were80～90%. As an alternate, cyano could also be reduced with sodium methylate as hydrogen donor. The reactions were performed in aprotic solvents at70℃, and the amines were obtained with yield around90%. Other unsaturated nitrogen-containing groups, such as nitro, imine, et al, were reduced with sodium alcoholates as promoter, and corresponding alcohols were used as hydrogen donor. The reactions were carried out at50-70℃, and the yields of corresponding amines were above80%. The product in the transfer hydrogenation of2-fluorobenzonitrile was1-H-indazole instead of2-fluoroaniline, and the reaction mechanism was proposed.Asymmetric transfer hydrogenated amination. Prochiral ketone, amine and formic acid could react with chiral Pd(II) complex as catalyst. The corresponding amine were obtained at50℃, and the yields were above90%with ee value between25%and86%.Calculation on transfer hydrogenation. Materials Studio was used to calculate the dehydrogenation of formic acid/formates, isopropanol and hydrazine on Pd surface, the conclusions obtained in the calculated results were in good agreement with the previous experiments. Gaussian03was used to calculate the cyclization of ortho-substituted phenylhydrazone, and a hydrogen bond induced mechanism was proposed which could give reasonable explanation on the experimental phenomina. Gaussian03was also used to calculate the asymmetric transfer hydrogenated amination. The conclusions obtained in the calculated results could not just give explanation on the experimental phenomina, but also give instruction to perform transfer hydrogenated amination of higher ee value.