Purification method of clevidipine butyrate intermediate

The invention discloses a purification method of 4-(2,3-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3-methyl carboxylate-5-carboxylic acid as an import intermediate for synthesizing clevidipine butyrate. The purification method comprises the following steps of: reacting the 4-(2,3-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3-methyl carboxylate-5-carboxylic acid with alkali to generate alkali metal salt; separating out the alkali metal salt from a solvent to achieve the impurity removal purpose; acidifying the alkali metal salt, and then reacting with n-butyric acid chloroformate to prepare the clevidipine butyrate. The purification method disclosed by the invention obtains high-purity high-yield monocarboxylic acid by effectively removing dicarboxylic acid impurities contained in the monocarboxylic acid intermediate through operation steps which are easy to operate and can obviously reduce the content of principal impurities contained in the clevidipine butyrate by adopting the prepared high-purity monocarboxylic acid intermediate, simplify the purification procedure of the clevidipine butyrate and increase the total yield.