The general procedure for the synthesis of 2,5-dichloro-p-xylene from p-xylene is as follows: In a 500 ml round-bottomed flask, 330 grams of p-xylene (3.1 moles), 0.50 grams (0.003 moles) of ferric chloride, and 0.58 grams (0.003 moles) of dibenzyl sulphide were added and mixed with stirring. The temperature of the mixture was raised to 30°C and 521 g of chlorine gas was slowly passed through the mixture at this temperature over a period of 8 hours. The temperature was gradually raised to about 60°C depending on the cure of the reaction mixture. Upon completion of the chlorination reaction, the crude product was analyzed by gas chromatography, which showed the following composition: degree of chlorination (number of moles of chlorine substituted for 1 mole of p-xylene) 2.21, 2,5-dichloro-p-xylene (2,5-DCPX) 74.5%, 2,3-dichloro-p-xylene (2,3-DCPX) 5.1%, trichloro-p-xylene 19.9%, tetrachloro-p-xylene 0.5%. Subsequently, the crude product was purged with nitrogen and distilled according to the same method as in Example 1 to obtain 255.6 g of crude 2,5-DCPX with a purity of 93.9%. 281.8 g of isopropanol was added thereto, heated to 60° C. to dissolve the crystals, and cooled to 19° C. to crystallize, to ultimately obtain 187 g (53.4% yield) of 2,5-DCPX with a 99.9% purity .
