Chlorobenzene → 4-(4-Chlorophenyl)-2-methyl-4-oxobutanoic acid

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To a solution of 114 g. of methylsuccinic anhydride in 400 ml. of chlorobenzene is added carefully 270 g. of aluminum chloride. The mixture is heated to 65° C. for 11/2 hours, is cooled, quenched with ice and concentrated hydrochloric acid and extracted with benzene. The benzene layer is extracted with aqueous sodium bicarbonate. After adjusting the pH of the bicarbonate solution to 6.3, concentrated hydrochloric acid is added slowly over a period of several hours with stirring. At pH 5.7, 78 g. of white crystals are filtered off. Recrystallization of this material from ethanol-water affords 3-(p-chlorobenzoyl)-2-methylpropionic acid as white crystals. A mixture of 35.50 g. of the preceding compound, 85 ml. of hydrazine hydrate and 400 ml. of ethyl alcohol is allowed to stir at reflux for 18 hours. The reaction mixture is concentrated to about 75% of the original volume, cooled in an ice bath and filtered to yield 26.62 g. of 6-(p-chlorophenyl)-4,5-dihydro-4-methyl-3(2H)-pyridazinone as a yellow solid. An additional 4.7 g. of product is obtained from the filtrate above.

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