Oxygen → 3-Chlorophthalic anhydride

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In a pilot scale reaction 200 kilograms (kg) of chloro-ortho-xylene (a mixture of 3-chloro-ortho-xylene and 4-chloro-ortho-xylene), 780 kg of acetic acid, 3.5 kg (1.0 mol %) cobalt acetate tetrahydrate, 1.7.5 kg (0.5 mol %) manganese acetate tetrahydrate, 0.4 kg (0.05 mol %) zirconium acetate solution, 1.75 kg (1.5 mol %) sodium acetate and varying amounts of sodium bromide were combined. The amount of sodium bromide was varied by example as shown in Table 2. The reactor was filled with nitrogen, pressurized to 1900 Kpa and heated to about 160° C. Air was introduced to the reactor through a dip tube at a flow rate gradually increasing to 200 normal m3/h. Initially, the off gas oxygen concentration was greater than 0 but less than 1 percent. The reaction mixture was agitated throughout the reaction time. After about 1 hour, the reaction temperature was increased to 175° C. After about 3 hours the off gas oxygen concentration increased to greater than 3 percent. The air flow was stopped. Air diluted with nitrogen so as to have an off gas oxygen concentration of about 5 percent was introduced into the reactor and the temperature of the reactor was increased to 190° C. The flow of diluted air was continued for about 3 hours. Final weight of the reactor contents was consistent with high conversions of chloro-o-xylene based on the absorption of 3 moles of O2 to generate the diacid and two moles of water. The majority of water formed by the reaction and the acetic acid were removed under atmospheric distillation. The chlorophthalic acid was dehydrated and any residual water and acetic acid were removed under heat and reduced pressure to form chlorophthalic anhydride. Chlorophthalic anhydride was separated from the catalyst by distillation under vacuum at distillation temperatures near 170° C. The isolated chlorophthalic acid was analyzed by gas chromatography. Results are shown in Table 2.

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