Introduction | Isonicotinic acid methyl ester, also known as pyridine-4-carboxylic acid methyl ester, is an important organic synthesis intermediate, mainly used in pharmaceutical production, it is also a good industrial solvent. At present, there are few reports on it at home and abroad. Isonicotinic acid and methanol are synthesized by direct esterification under the action of concentrated sulfuric acid. However, concentrated sulfuric acid, as a traditional esterification catalyst, is easy to oxidize and carbonize organic matter, leading to a series of side reactions, serious corrosion of equipment and difficult treatment of three wastes. Therefore, exploring new catalysts to replace concentrated sulfuric acid has become a research hotspot. |
preparation | (1) a mixture of acetonitrile, hydroxylamine hydrochloride and sodium methoxide was stirred at room temperature for 2-4 days, the mixture had a molar ratio of acetonitrile: hydroxylamine hydrochloride: sodium methoxide of 1:1:1, then filtered and the filtrate was concentrated below 20 °c to yield (Z) as a white solid-N'-hydroxyethanamidine;(2) refluxing a mixture of methanol, potassium hydroxide and dimethyl pyridine-2, 4-dicarboxylate for 0.5-2 hours, then evaporated in vacuo to produce 4-(methoxycarbonyl) picolinic acid as a yellow solid;(3) add oxalyl chloride to 4-(methoxycarbonyl) picolinic acid in dichloromethane, keeping the temperature at 25-30 °c for 3 days, the reaction was evaporated in vacuo, To produce methyl 2-(chlorocarbonyl) isonicotinate as a yellow oil;(4) Add (Z)-N'-hydroxyacetamidine and triethylamine to 2-(chlorocarbonyl) A solution of methyl isonicotinate in dichloromethane, maintaining the temperature at 25-30 °c for 0.5-2 days, the reaction was concentrated in vacuo to yield 2-((1-aminoethylaminooxy) carbonyl) Isonicotinic Acid (Z)-methyl ester as a yellow solid;(5) A solution of 2-((1-aminoethylaminooxy) carbonyl) Isonicotinic Acid (Z)-methyl ester in toluene is heated under reflux for 12-36 hours, the resulting mixture was evaporated and purified by silica gel column chromatography to give 2-(3-methyl -1,2, 4-oxadiazolyl-5-yl) Isonicotinic acid methyl ester;(6) lithium hydroxide, ethanol and 2-(3-methyl -1,2, the mixture of methyl 4-oxadiazolyl-5-yl) isonicotinate is stirred at room temperature for 2-10 hours, then the mixture is concentrated in vacuo, water is added and then extracted with ethyl acetate, the aqueous layer was brought to pH 1.5 with 1N aqueous hydrochloric acid and extracted with ethyl acetate;(7) the organic layer was concentrated in vacuo to yield the compound as a white solid, I .e., Isonicotinic acid. 1HNMR(300MHz,DMSO-d6)δppm14.08(brs,1H)9.00-8.98(m,1H)8.50(s,1H)8.09-8.07(m,1H) 2.46(s,3H). (8) preparation of catalyst S2O2-8/ZrO2-SiO2 a certain amount of ZrOCl2 · 8H2O and NaSiO3 · 9H2O were weighed and hydrolyzed with 8% dilute ammonia water to adjust the pH value of the solution to 9; aging was carried out at 0 ° C. For 24h, Suction filtration, and washing with distilled water until Cl-free (checked with 0.1mol/L AgNo3 solution). Drying at 110 ° C, grinding 100 mesh sieve; According to the ratio of 15ml/g, with 0.5mol/L ammonium persulfate solution immersion 8H; Suction filtration, drying under infrared lamp, it was calcined in a muffle furnace at 500 °c for 3H. The solid superacid catalyst S2O2-8/ZrO2-SiO2 was prepared and placed in a desiccator for standby. (9) add 6.2g(0.05mol) of Isonicotinic Acid and 16.2mL(0.4mol) of anhydrous methanol to a 250mL three-necked flask equipped with a water trap, a thermometer and a reflux condenser, 0.5g solid superacid catalyst, heated to reflux on a magnetic stirrer to separate water, The reaction was maintained for about 3H. Stop heating, cool, filter and separate the solid superacid catalyst. After the reaction solution is layered, the reaction solution is neutralized and washed with saturated Na2CO3 solution, and then dried with anhydrous MgSO4, after vacuum distillation, the fraction of 95~100 ℃(2.67KPa) was collected to obtain a slightly brownish yellow transparent liquid, which is methyl isonicotinate after drying. |