[Cl:1][CH:2]1[CH:12]=[CH:11][CH:5]2[C:6]([O:8][C:9](=[O:10])[CH:4]2[CH2:3]1)=[O:7].BrBr.ClCl.Br>ClC1C=CC=CC=1>[Cl:1][C:2]1[CH:3]=[C:4]2[C:9](=[O:10])[O:8][C:6](=[O:7])[C:5]2=[CH:11][CH:12]=1
A mixture of 93 g (0.5 moles) of 4-chlorotetrahydrophthalic anhydride and 30 g of monochlorobenzene was heated and maintained at 105° C. TO 135° C. while 80 g (0.5 moles) of bromine was added over a three hour period. Simultaneously, chlorine gas (0.5 moles) was added to the vapor space above the organic liquid. As the HBr off-gas from the reaction of bromine with 4-chlorotetrahydrophthalic anhydride exited, it contacted the chlorine gas and the resultant bromine was condensed back into the organic liquid phase for reuse. A total of 36.45 g (0.5 moles) of chlorine were consumed during this time. The reaction mixture was finally heated to 165°-175° C. for an additional 5 hours. The crude reaction mixture was distilled resulting in isolation of 86% of 4-chlorophthalic anhydride.
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