3,4-Dichlorobenzaldehyde (5.0 g, 28.60 mmol), methyltriphenylphosphonium bromide (20.40 g, 57.20 mmol), and potassium carbonate (9.90 g, 71.50 mmol) were used as raw materials, which were dissolved in 110 mL of a solvent mixture of dioxane and water (V/V = 10:1). The reaction mixture was heated to 95 °C and the reaction was stirred at this temperature for 12 hours. Upon completion of the reaction, the organic phases were combined and washed with saturated sodium chloride solution (50 mL x 3) and subsequently dried over anhydrous sodium sulfate. The dried organic phase was filtered and the filtrate was concentrated under reduced pressure. The resulting residue was purified by column chromatography using eluent system B as eluent, and the target product 1,2-dichloro-4-vinylbenzene (4.0 g, colorless liquid) was finally obtained in 80.9% yield.
