2,5-Dichlorophenol → Potassium 2,5-dichlorophenolate

A solution of 81.5 gm (0.50 mol) of 2,5-dichloro-phenol in 400 ml of xylene was boiled with 31.8 gm of 88% caustic potash (corresponding to 0.50 mol KOH) in a vessel equipped with an efficient water trap comprising a water-cooled phase separation tube until no more water separated out of the distillate. An anhydrous solution of potassium 2,5-dichlorophenolate in xylene was thus obtained. This solution was filtered and then charged into a shaker autoclave having a capacity of 2 liters, which had been warmed to 40° C. 104 gm (0.75 mol) of finely powdered, anhydrous potassium carbonate were then added to the contents, and the autoclave was flushed with carbon dioxide and then closed. The contents of the autoclave were now shaken for 25 minutes at 40° C. while introducing carbon dioxide at a pressure of 40 bars. Thereafter, the introduction of carbon dioxide was discontinued, and the contents of the autoclave were shaken at 140° C. for 15 hours, whereby the internal pressure rose to 70-80 bars. The contents of the autoclave were now allowed to cool to below 60° C., the pressure was released, and the autoclave was subsequently emptied by first rinsing it with xylene and then with a total of 700 ml of water. The xylene phases, including the solid matter contained therein, were combined. The solid matter was separated from the xylene mother liquor by suction filtration and then dissolved in the aqueous phase. The aqueous solution thus obtained was made strongly acid with concentrated hydrochloric acid, whereupon 3,6-dichloro-salicylic acid precipitated out. The precipitate was collected by suction filtration and, together with three liters of water, subjected to steam distillation. Any dichlorophenol and xylene still present passed over with the steam, whereas the desired product remained in the distillation vessel. When the distillate passing over was clear, the distillation was stopped. The contents of the distillation vessel were now filtered while still hot, and the filtrate was cooled, whereupon the product crystallized out. It was collected by suction filtration and dried (1st product fraction).