Step 1: A methanol (2L) solution of 2,5-dibromobenzoic acid (250 g, 0.90 mol) and concentrated sulfuric acid (18.4 g, 0.19 mol) were added to a 2L round bottom flask. The reaction mixture was heated to reflux overnight and subsequently cooled to room temperature. The resulting precipitate was collected by filtration, washed with cold methanol and dried under vacuum to give 203.6 g of methyl 2,5-dibromobenzoate as a yellow solid. Step 2: To another 2L round-bottomed flask was added a solution of methyl 2,5-dibromobenzoate (198.2 g, 0.68 mol) in anhydrous DMF (1L). Copper cyanide (122 g, 1.36 mol) and sodium iodide (22.8 g, 0.15 mol) were subsequently added. The mixture was stirred at 130 °C overnight under nitrogen protection. Upon completion of the reaction, extraction was carried out with ethyl acetate (500 mL x 3), the organic layer was washed with water (500 mL), and finally purified by silica gel column chromatography (petroleum ether/ethyl acetate = 5/1) to afford 95.2 g of methyl 2,5-dicyanobenzoate as a brown solid in 75.1% yield.
