Trichloroacetaldehyde method guaiacol and trichloroacetaldehyde are heated to 27 ℃ in the presence of soda ash or potassium carbonate to condense to form 3-methoxy-4-hydroxyphenyltrichloromethyl methanol. Famolin was removed by steam distillation. In the presence of caustic soda, use nitrobenzene as an oxidant and heat to 150 ℃ to oxidatively crack to obtain vanillin; Cu-CuO-CoCl2 can also be used as a catalyst for air oxidation at 100 ℃, and after the reaction, benzene is used to extract vanillin, The finished product is obtained by distillation under reduced pressure and recrystallization.
In the glyoxylic acid method, guaiacol, sodium hydroxide solution and sodium carbonate are sequentially added to the glyoxylic acid solution, and 3-methoxy-4-hydroxyphenyl glycolic acid is formed by condensation at 30-33 °C. After extracting the unreacted guaiacol with a solvent, adding sodium hydroxide solution, heating to 100°C in the presence of nitrobenzenesulfonic acid and calcium hydroxide for oxidative cracking to obtain vanillin. After neutralization of the oxidized product, vanillin is extracted with dichloroethane, and the crude product is purified by vacuum distillation and recrystallization to obtain the finished product. Nitroso method: Add 166kg of 30% hydrochloric acid and 200kg of water into the reaction kettle, and after cooling to 10°C, add 61.5kg of dimethylaniline dropwise within 2h, the temperature does not exceed 25%, and then continue to stir for 20min. After cooling to 6 ℃, add dropwise a 25% aqueous solution prepared by 75 kg of sodium nitrite, and keep stirring at 7~10 ℃ for 1 h. Filter out p-nitrosodimethylaniline hydrochloride, then add a certain amount of ethanol and concentrated hydrochloric acid to dilute the solid to obtain p-nitrosodimethylaniline.
Condensation of guaiacol and p-nitrosodimethylaniline: dissolve 26kg of urotropine in 34kg of water, add a mixture of 126kg of guaiacol and 63kg of ethanol, and store in a high-level tank for later use. The mixed Chemical 550kg of the above-mentioned p-nitrosodimethylaniline hydrochloride and ethanol was added to the reactor, and after being heated to 28°C, a metal salt catalyst was added, and then guaiac was added dropwise when being heated to 35～36°C. The temperature of the phenol mixture (3～3.5h) was kept at 40～43℃, and the stirring reaction was continued for 1h after the dropwise addition. Then add 100kg of water at 40°C to dilute, and stir for 15min. The content of vanillin in the condensate should be above 11%.
Using benzene as a solvent, the above-mentioned condensed liquid is continuously extracted in countercurrent in a rotating disk liquid-liquid extraction tower. The benzene extract contains a large amount of hydrochloric acid, which is first washed with water, and then neutralized to Ph=4 with alkali; benzene is recovered by distillation with a rising film evaporator, and then steamed for 1 hour to remove residual benzene; then evaporated under reduced pressure water, and finally the crude vanillin is quickly distilled at 120-150°C (666.6Pa), and the freezing point is about 70°C. The crude product was dissolved in toluene at 70°C, filtered and cooled to 18-20°C, filtered with suction and washed with a small amount of toluene to obtain vanillin. Then carry out the second vacuum distillation, collect the fractions at 130-140°C (266.6-399.9Pa) and dissolve them in dilute ethanol at 60-70°C, slowly cool to 16-18°C to crystallize (1h) . Filter by centrifuge and wash with a little dilute ethanol. Finally, at 50 ~ 60 ℃, hot air drying for 12h to obtain the finished product. According to guaiacol, the yield can reach more than 65%.