NOVELTY - Clean production of vanillin includes dropwise adding into a reaction flask, glyoxylic acid, guaiacol and sodium hydroxide solution, controlling the temperature and pH while feeding the raw materials, after addition of raw materials is complete, continuously reacting to complete the condensation reaction, adding the condensation reaction liquid with sulfuric acid to adjust the pH, extracting unconverted guaiacol with toluene, obtaining vanillin intermediate i.e. 3-methoxy-4-hydroxymandelic acid (MHMA) reaction liquid and measuring MHMA content of reaction liquid.    USE - Clean production of vanillin (claimed).    ADVANTAGE - The method uses silver nitrate as oxidizing agent, which increases oxidation yield and shortens oxidation reaction time, provides two kinds of fine chemical products, fully utilizes the raw materials, reduces the generation of waste products and production cost, is safe and has environmental protection.    DETAILED DESCRIPTION - Clean production of vanillin comprises dropwise adding into a reaction flask, glyoxylic acid, guaiacol and sodium hydroxide solution, where mol ratio of glyoxylic acid, guaiacol and sodium hydroxide is 1:1.0-1.2:2-5, controlling the temperature at 20-40 degrees C and pH at 11-13 for 1-2 hours while feeding the raw materials, after addition of raw materials is complete, continuously reacting for 4-6 hours to complete the condensation reaction, adding the condensation reaction liquid with 10 mass% sulfuric acid to adjust the pH at 5-6, extracting unconverted guaiacol with toluene, obtaining vanillin intermediate i.e. MHMA reaction liquid, measuring MHMA content of reaction liquid, adding silver nitrate solution into glass reactor, adding MHMA reaction liquid and sodium hydroxide solution, where mol ratio of silver nitrate, MHMA and sodium hydroxide is 1:0.45-0.55:1.0-1.2, generating gray white precipitates, maintaining temperature at 20-40 degrees C and pH at 11-13 for 0.5-1 hour while feeding the materials, after feeding is complete, raising the temperature to 50-60 degrees C, reacting with continuous stirring for 0.5-1 hour, after completely oxidizing MHMA, adding formic acid to recover excess amount of silver nitrate, where mol ratio of silver nitrate and formic acid is 1:0.02-0.1, separating silver powder by filtering, washing with deionized water and alcohol, drying at 80 degrees C to obtain superfine silver powder product having quality, which meets the solar battery requirements, and yield of 99.4-100 mol.%, adding the filtrate with 10 mass% sulfuric acid solution to acidify at pH 1-2, decarboxylating MHMA at 30-50 degrees C, extracting the decarboxylation reaction liquid with toluene, washing the organic phase with little amount of water, measuring the vanillin content at 96.8-98.5 mol.% in terms of MHMA, recovering toluene solvent by vacuum distillation, and recrystallizing the residue with ethanol aqueous solution to obtain white vanillin.