Industrial preparation method of 4,7-dichloroquinoline

The invention relates to a preparation method of a medical intermediate 4,7-dichloroquinoline. The 4,7-dichloroquinoline is an important intermediate of a medicine hydroxychloroquine sulfate for treating discoid lupus erythematosus and systemic lupus erythematosus. The preparation method comprises the following steps: performing hydrolysis and acid adjustment on 4-hydroxyl-7-chlorine-quinoline-3-carboxylic acid ethyl ester by using 10% sodium hydroxide solution to prepare 4-hydroxyl-7-chlorine-quinoline-3-carboxylic acid; performing decarboxylation to produce 4-hydroxyl-7-chloroquinoline; and chlorinating the 4-hydroxyl-7-chloroquinoline by using phosphorus oxychloride to obtain 4,7-dichloroquinoline crude products; and performing one-step refining to obtain the products. The purity of the prepared products is more than or equal to 99% and the total yield of the products is more than or equal to 70%; raw materials are easily available; the process is simple; the yield and the purity are high in each step; and the preparation method is suitable for industrialized production.