NOVELTY - 2-Keto-L-gulonic acid, 1-8C alcohol and bifunctional solid catalyst are added to inert solvent, stirred and reacted. The reaction temperature is controlled in order to stop reaction, and 1-8C alcohol and water are distilled. The reaction mixture is cooled, filtered, the obtained brown solid mixture is dissolved in deionized water, pulped, filtered and washed, to obtain recycled catalyst and filtrate. Activated carbon is added to the filtrate, concentrated, cooled, crystallized, filtered, vacuum-dried and refined to obtain vitamin C.    USE - Synthesis of vitamin C.    ADVANTAGE - The method produces vitamin C, with reduced wastewater discharge.    DETAILED DESCRIPTION - 2-Keto-L-gulonic acid (2-KLG), 1-8C alcohol and acid-and-alkali bifunctional solid catalyst (5-25 weight% of 2-KLG) are added to inert solvent, stirred, warmed and reacted in initial stage at 55-85 degrees C for 1.5-3.5 hours and final stage at 45-100 degrees C for 2.5-8.5 hours. The molar ratio of 2-KLG and 1-8C alcohol is 1:3-7. The inert solvent is halohydrocarbon, ether or aromatic solvent. The reaction temperature is controlled by stirring for predetermined time in order to stop reaction, and then 1-8C alcohol and water are distilled under reduced pressure, the reaction mixture is cooled to room temperature and filtered, to obtain brown solid mixture. The solid mixture is dissolved in deionized water, pulped, filtered and the obtained filter dreg is washed using water and solvent, to obtain recycled catalyst and filtrate which is vitamin C solution. Activated carbon is added to the filtrate for decolorization, concentrated under reduced pressure, cooled, crystallized, filtered, vacuum-dried and refined to obtain vitamin C. The recycled catalyst is washed using water-containing high polar organic solvent, filtered and dried to obtain reusable catalyst. The high polar organic solvent is 1-5C alcohol, 1-6C halohydrocarbon, 6-10C aromatic hydrocarbon, 2-10C ether, 1-7C nitro compound, dimethyl sulfoxide and dimethylformamide.