Process for the preparation of halogenated carboxylic anhydrides

Abstract

The present invention relates to a process for the preparation of halogenated carboxylic anhydrides, e.g. for the preparation of trifluoroacetic anhydride. The preparation is achieved by reacting a halogenated carboxylic acid, e.g. trifluoroacetic acid, with sulfuric acid, oleum and/or disulfuric acid.

Claims

1. A process for the preparation of trifluoroacetic anhydride, the process comprising reacting trifluoroacetic acid with oleum.

2. The process of claim 1 wherein the oleum contains from 5 to 95 wt % free SO.sub.3.

3. The process of claim 1 wherein the trifluoroacetic acid is present in molar excess relative to the stoichiometry of the reaction.

4. The process of claim 1 wherein the reaction is performed at a temperature in the reaction mixture from 50 to 150° C.

5. The process of claim 1 wherein the trifluoroacetic anhydride is removed from the reaction mixture by distillation.

6. The process of claim 5 wherein the distillation is performed using a packing column.

7. The process of claim 5 wherein the distillation is performed using a reflux condenser for controlling the rate at which the trifluoroacetic anhydride is removed from the reaction mixture.

8. The process of claim 1 wherein the reaction is performed in a reaction vessel which is at least partially ceramic-lined and/or glass-lined.

9. The process of claim 1 wherein the reaction is performed in a reaction vessel at least partially made of an alloy containing nickel and/or molybdenum.

10. The process of claim 1 wherein the trifluoroacetic acid employed in the process has a purity of equal to or less than 98%.

11. The process of claim 1 wherein the trifluoroacetic acid employed in the process is recycled material.

12. The process of claim 1 wherein the trifluoroacetic acid is employed comprised in a mixture also containing at least one product, one reagent, one solvent and/or one side product from a previous reaction step.

13. The process of claim 2 wherein the oleum contains from 25 to 80 wt % free SO.sub.3.

14. The process of claim 13 wherein the oleum contains from 50 to 70 wt % free SO.sub.3.

15. The process of claim 4 wherein the reaction is performed at a temperature in the reaction mixture from 70 to 115° C.

16. The process of claim 10 wherein the trifluoroacetic acid employed in the process has a purity of less than 95%.

17. The process of claim 16 wherein the trifluoroacetic acid employed in the process has a purity of less than 90%.

Description

EXAMPLES

Production of Trifluoroacetic Anhydride

(1) A 115 l ceramic-lined Pfaundler stirred vessel equipped with a 2.5 m packing column filled with 10 mm glass Raschig rings and equipped with a condenser was filled with 70.5 kg trifluoroacetic acid followed by 19.1165% oleum, i.e. oleum with 65 wt % free SO3. Subsequently, the Pfaundler vessel was heated by means of an oil bath to a temperature of 130° C. The product was removed by distillation at a rate of 7.4 kg/h and directed into PE-lined metal drums. During the distillation the temperature of the reaction mixture changed gradually from 78° C. to 96° C. The yield of trifluoroacetic anhydride was 64.9 kg (99%). The purity of the product was >99.9%. Additionally, 7.8 kg of a tailing fraction was obtained that contained trifluoroacetic anhydride and trifluoroacetic acid next to other not identified side products. This second fraction can be submitted to the reaction mixture of a subsequent batch.