(1) Mix 2-amino-5-methylpyridine, diazotization reagent, and water evenly, cool to -4°C-3°C, add an acid solution for insulation reaction; after the reaction is complete, heat for hydrolysis and cooling, and then use mass A 30% sodium hydroxide solution is used to adjust the pH to 6.5-7.5, the organic phase is extracted with the first solvent, dried and concentrated under reduced pressure to obtain a crude 2-hydroxy-5-methylpyridine;
(2) Adding the second solvent to the crude 2-hydroxy-5-methylpyridine, heating to reflux, cooling and crystallization, suction filtration and drying to obtain pure 2-hydroxy-5-methylpyridine.
Mix 21.6g of 2-amino-5-picoline, 20.7g of diazotization reagent sodium nitrite and 40g of cold water at 5°C in a mixer to form a paste, then add ice to cool the paste to 0°C, Then, the paste was slowly poured into a continuously stirred hydrochloric acid solution with a concentration of 12% by mass, and the reaction was stirred at 0° C. for 1 hour to complete the reaction. Then heated to 95°C for 30min, cooled to 20°C, adjusted to pH 7 with 50% sodium hydroxide solution, heated to 60°C, extracted with ethyl acetate 150ml×5, and combined the organic layers , dried over anhydrous sodium sulfate, filtered, and the filtrate was concentrated under reduced pressure to obtain 18.4 g of a pale yellow solid crude product; then 55 ml of anhydrous ethanol was added, heated to reflux for 1 h, cooled to 2°C, crystallized for 6 h, filtered with suction, and washed with anhydrous ethanol. , and dried at 50° C. for 8 hours to obtain 15.3 g of yellowish crystalline 2-hydroxy-5-picoline, with a yield of 70.2%.
Preparation of raw materials: Weigh 1000g of 5-methyl-3,4-dihydropyridine-2(1H)-one with a content of 95%, put it into a four-necked flask containing 1000g of chlorobenzene, stir to completely dissolve it and wait for it to be completely dissolved. use.
Pyridine phenol synthesis: The reaction process adopts a continuous flow micro-channel reactor, and feeds simultaneously according to the ratio of raw material pyridone chlorobenzene liquid to chlorine gas substance of 1:1.05. The temperature of the first three plates is 50 °C, and the temperature of the last three plates is 160 °C. In the fourth plate, a sodium carbonate aqueous solution (sodium carbonate content of 10%) of the same quality as pyridone was pumped. The residence time of the reaction material is controlled to be 90s by adjusting the flow rate of the pump, the pyridinephenol chlorobenzene liquid is continuously discharged and collected, and DMF (accounting for 12% by weight of pyridine) is added to it for the next reaction.