Synthesis
In a 300 ml HC4 autoclave, at 20 bar carbon monoxide pressure and 130°C, a solution of 10 g of 5 g water [278 mmol] and 5 g of N-methylpyrrolidone was added to a solution of 49 g of 2,4-dichlorobenzyl chloride [252.5 mmol] and 18 mg of palladium chloride [0.1 mmol] in 105 g of N-methylpyrrolidone over 1 hour. The pressure was kept constant at 20 bar during the addition. After 16 hours, the mixture was further stirred to constant pressure. After cooling, N-methylpyrrolidone and hydrogen chloride were separated at 150°C and 200 mbar. The residue was added as a melt to water with parallel addition of 50% aqueous sodium hydroxide solution to maintain pH 10. A homogeneous solution was obtained and extracted with 20 ml xylene to remove organic soluble substances. The mixture was then acidified to pH 1 with approximately 30% aqueous hydrochloric acid solution, and 2,4-dichlorophenylacetic acid precipitated as a white solid.
The precipitated product was washed with water until the effluent had a constant pH. The washed product was dried at 100°C under reduced pressure to give 2,4-dichlorophenylacetic acid. Yield: 89%. GC purity: 100%. Melting point: 131-133°C.
