Preparation of 1-methyl-1H-pyrazole-4-boric acid

Background and overview.

1-methyl-1H-pyrazole-4-boric acid is an organic intermediate, which can be prepared by the reaction of 1-methyl-4-bromopyrazole with triisopropyl borate. 1-methyl-1H-pyrazole-4-boric acid can react with pinacol to give 1-methyl-4-(4-tetramethyl-5-tetramethyl-1-methylidene-2-yl)-1H-pyrazole, which is an important chemical intermediate.

 

 

Preparation

 

(1) vacuum pumping 580L tetrahydrofuran with 99.9% purity and 0.1% moisture into the cryogenic reactor with stainless steel coil in 1000L jacket with motor power 5.5KW and rotating speed of 80 rpm / min, and then pumping 1-methyl-4-bromopyrazole with 80kg purity of 98.0% into the cryogenic kettle and stirring 20min to make it mix evenly. The reactor is replaced with nitrogen for 3 times to ensure the absence of oxygen. The stirring in the following operation process is always open and cannot be stopped. Then the inner coil is put into liquid nitrogen, the temperature of the reactant is cooled to 70 ℃, and 2.5m n-butyl lithium 163.68kg is slowly dripped at 70 ℃, the dripping speed is controlled at about 8h25min, the dripping speed is too fast, the temperature is difficult to control, the dripping acceleration is too slow, the reaction time is too long, the impurities can not be removed, and the product yield is low and the purity is reduced.

(2) keep the temperature of-80 ℃ at 70 ℃, continue to add 98.0% triisopropyl borate 103.4kg, control the dripping rate when using 1h30min, and continue the reaction at this temperature for 2 hours.

(3) after heating the reaction mixture to-15 ℃, it was neutralized with 15% ammonium chloride aqueous solution of 150ml. Heat the mixture to room temperature and heat to room temperature. Stir for 1 hour. The organic layer is separated and the water layer is extracted with 100ml THF. The merged organic dries the water layer by Na2SO4 and evaporates the solvent. Under decompression. The residue was washed with ether (2 × 50 ml) and dried in vacuum to obtain white 1-methyl-1H-pyrazole-4-boric acid.