Preparation of 3-chlorophthalic anhydride
AssigneeBASF SE
InventorsKarl Gerhard Baur, Erwin Brunner, Eckhardt Brandt
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Abstract
A process for preparing essentially pure 3-chlorophthalic anhydride from a mixture in which 3-chlorophthalic anhydride is present in addition to 4,5-dichlorophthalic anhydride, which involves first distilling off a mixture of 3-chlorophthalic anhydride and 4,5-dichlorophthalic anhydride, so that the obtained bottoms is essentially free of 4,5-dichlorophthalic anhydride, and then by distillation of the obtained bottoms, recovering 3-chlorophthalic anhydride in a second distillation step. The starting mixture is preferably prepared without solvent in a melt by incomplete chlorination of phthalic anhydride using FeCl.sub.3 as a catalyst.
Claims10
A process for preparing substantially pure 3-chlorophthalic anhydride from a starting chlorination products mixture which contains 4,5-dichlorophthalic anhydride in addition to 3-chlorophthalic anhydride, which comprises first distilling off a mixture of 3-chlorophthalic anhydride and 4,5-dichlorophthalic anhydride from the starting chlorination products mixture in a distillation step (a), so that the bottom obtained is essentially free of 4,5-dichlorophthalic anhydride, and then, by distillation of the bottom obtained, recovering 3-chlorophthalic anhydride from chlorination products in a distillation step (b), wherein the purity of the 3-chlorophthalic anhydride is controlled by reflux ratio during the separation of the mixture of 3-chlorophthalic anhydride and 4,5-dichlorophthalic anhydride in the distillation step (a).
A process for the production of substantially pure 3-chlorophthalic anhydride which comprises chlorinating phthalic anhydride with partial conversion to obtain a chlorination products mixture, distilling off unreacted phthalic anhydride as a top product, distilling off 4-chlorophthalic anhydride as a second top product, then distilling off a mixture of 4,5-dichlorophthalic anhydride and 3-dichlorophthalic anhydride as a third top product to obtain a bottoms product which is essentially free of 4,5-dichlorophthalic anhydride, and recovering by subsequent distillation substantially pure 3-dichlorophthalic anhydride.
Dependencies are inferred from the claim text.