Study On The Synthesis Of 4-Chlorophthalic Anhydride

4-Chlorophthalic anhydride is an important chemical intermediate which is broadly used in producing dyes, plastic, medicines, and pesticides. Currently, looking for some industrial potential synthesis routes, in which the technologcial conditions are reasonable and the materials can be easily obtained, has already become the point of research.Two routes that using phthalic anhydride and butadiene respectively as the starting material to synthesize 4-chlorophthalic anhydride are researched in this paper. In the route of using phthalic anhydride as the starting material, 4-chlorophthalic anhydride is synthesized through three consecutive reactions. Phthalic anhydride is firstly nitrified by oil of vitriol and nitric acid. Then the targeted product 4-nitrophthalic acid is separated from 3-nitrophthalic acid through two methods named extraction and esterification-hydrolysis. The optimum reaction conditions of both the two methods are obtained by orthogonal experiments. Under the optimum reaction conditions of the extraction method, the yield and purity of 4-nitrophthalic acid are of 53.4% and 83%, respectively. The relating results of the esterification-hydrolysis method are of 48.3% and more than 99%, respectively. 4-Nitrophthalic anhydride is obtained in 86.2% yield by the dehydration of 4-nitrophthalic acid. Finally, 4-chlorophthalic anhydride is obtained by the chlorination of 4-nitrophthalic anhydride and its acid. 3-chlorophthalic anhydride is found in the chlorination product by the analysis of HPLC/MS. The total yield of both the two isomers is of 89-95%.In the route of using butadiene as the starting material, tetrahydrophthalic anhydride is firstly synthesized by the Diels-Alder reaction of butadiene with maleic anhydride in a yield of as high as 99.1%. Tetrahydrophthalic acid is obtained by the hydrolysis of Tetrahydrophthalic anhydride in 85.9% yield. Then, tetrahydrophthalic anhydride and its acid are treated by chlorine in different solvents. The product of chlorination in water is 4,5-dichlorocyclohexane-1,2-dicarboxylic acid. Finally, the dehydrochlorination and aromatization reactions of 4,5-dichlorocyclohexane-1,2-dicarboxylic acid are explored in this paper.