Method for producing acyloxy benzoic acids

1. A process for preparing an acyloxybenzoic acid of the formula (I)

in which

R 1 is a linear or branched, saturated alkyl group having 6 to 30 carbon atoms, a linear or branched, singly or multiply unsaturated alkenyl group having 6 to 30 carbon atoms, or an aryl group having 6 to 30 carbon atoms,

comprising the steps of

a) reacting a carboxylic halide of the formula R 1 COHal, in which R 1 is defined above and Hal is a halide, with para-hydroxybenzoic acid in the presence of base, wherein the base is selected from alkali metal hydroxides, in a solvent mixture comprising water and at least one organic solvent, wherein the organic solvent is isopropanol, at a temperature ≦25° C. and a pH of 9 to 11.5,

b) adjusting the pH of the reaction mixture after step a), at a temperature ≦25° C., to a pH of 6 to 8 by addition of acid, and

c) subsequently heating the reaction mixture after step b) to a temperature of 35 to 80° C. and thereafter adjusting the pH of the reaction mixture to a pH of 1 to 4 by addition of acid.

2. The process as claimed in claim 1 , wherein after step c) the reaction mixture is cooled to a temperature <35° C.

3. The process as claimed in claim 1 wherein the acyloxybenzoic acids of the formula (I) are present in the form of particles having d 50 values of 10 to 150 μm.

4. The process as claimed in claim 3 , wherein the particles have d 10 values of 5 to 30 μm and d 90 values of 30 to 200 μm.

5. The process as claimed in claim 1 , the base in step a) is KOH or NaOH.

6. The process as claimed in claim 1 , the acid in steps b) and c) has a pKa value of less than or equal to 4.0.

7. The process as claimed in claim 1 , the acid in steps b) and c) is H 2 SO 4 or HCl.

8. The process as claimed in claim 1 , wherein the weight ratio of water to the at least one organic solvent in step a) is from 5:1 to 1:5.

9. The process as claimed in claim 1 , wherein the weight ratio of water to para-hydroxybenzoic acid in step a) is from 2:1 to 10:1.

10. The process as claimed in claim 1 , wherein R 1 is a linear or branched, saturated alkyl group having 6 to 30 carbon atoms, or a linear or branched, singly or multiply unsaturated alkenyl group having 6 to 30 carbon atoms.

11. The process as claimed in claim 10 , wherein the radical R 1 is an alkyl group.

12. The process as claimed in claim 10 , wherein a carboxylic acid, R 1 —COOH from which the carboxylic halide R 1 —COHal is derived is selected from the group consisting of octanoic acid, nonanoic acid, 3,3,5-isononanoic acid, decanoic acid and dodecanoic acid.

13. The process as claimed in claim 12 , wherein the carboxylic acid from which the carboxylic halide R 1 —COHal is derived is decanoic acid.

14. The process as claimed in claim 1 , wherein the amount of dimers and trimers of para-hydroxybenzoic acid present in the acyloxybenzoic acid produced is less than 0.3% by weight.

15. The process as claimed in claim 14 , wherein the amount of dimers and trimers of para-hydroxybenzoic acid present in the acyloxybenzoic acid produced is less than 0.1% by weight.

16. The process as claimed in claim 1 , wherein the acyloxybenzoic acid produced is free from unreacted para-hydroxybenzoic acid.

17. The process as claimed in claim 1 , wherein the acyloxybenzoic acid produced is free from acid of the formula R 1 COOH.

18. The process as claimed in claim 1 , wherein the acyloxybenzoic acids of the formula (I) are present in the form of particles having d 50 values of 10 to 150 μm, obtained directly from the process without subsequent treatment.

19. The process as claimed in claim 18 , wherein the particles have d 10 values of 5 to 30 μm and d 90 values of 30 to 200 μm, obtained directly from the process without subsequent treatment.