Method for producing acyloxy benzoic acids

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

wherein

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) admixing para-hydroxybenzoic acid, in a solvent mixture comprising water and at least one organic solvent, with an alkali metal hydroxide, in an alkali metal hydroxide : para-hydroxybenzoic acid molar ratio ≧1.9:1 and only thereafter adding a carboxylic halide of formula R 1 COHal, in which R 1 is defined above and Hal is a halide, at a temperature ≦25° C., and carrying out reaction,

b) adjusting the reaction mixture after step a), at a temperature ≦25° C., to a pH of 6 to 8.5 by addition of acid, if the pH at the end of step a) is not already within this range,

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

e) adding the entire amount of alkali metal hydroxide in step a) before the addition of the carboxylic halide to the reaction mixture, and otherwise adding no further base in the process.

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 alkali metal hydroxide in step a) is KOH or NaOH.

4. The process as claimed in claim 3 , wherein the alkali metal hydroxide in step a) is KOH.

5. The process as claimed in claim 1 , wherein the at least one organic solvent in step a) is selected from the group consisting of linear or branched alcohols, open-chain ethers, or and cyclic ethers.

6. The process as claimed in claim 5 , wherein the at least one organic solvent in step a) has from 1 to 10 carbon atoms.

7. The process as claimed in claim 6 , wherein the at least one organic solvent in step a) is selected from the group consisting of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, diethyl ether, tetrahydrofuran, dioxane, and mixtures thereof.

8. The process as claimed in claim 7 , wherein the organic solvent in step a) is isopropanol.

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

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

11. 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.

12. 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.

13. 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.

14. The process as claimed in claim 13 , wherein the radical R 1 is an alkyl group.

15. The process as claimed in claim 13 , 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.

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

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

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

19. The process as claimed in claim 1 , wherein the reaction mixture is cooled to a temperature of from 5° C. to 25° C. after step c).

20. The process as claimed in claim 1 , wherein step a) is carried out at a temperature of from 0° C. to 15° C.