Process for forming 2-hydroxypyridine-1-oxide or derivatives thereof

1. A process comprising the steps of:

(a) providing a solution comprising:

(i) at least one solvent, wherein the solvent is selected from the group consisting of ethanol, methanol, and mixtures thereof;

(ii) at least one acid;

(iii) at least one compound according to Formula (1)

wherein

R 1 is selected from the group consisting of H, a non-substituted or halogen-substituted, branched or unbranched C 1 -C 20 -alkyl radical, a non-substituted or halogen-substituted C 5 -C 8 -cycloalkyl radical, a non-substituted or halogen-substituted C 8 -C 10 -aryl radical or a non-substituted or halogen-substituted, branched or unbranched C 7 -C 20 -aralkyl radical;

R 2 is either O or S,

R 3 is H or a branched or unbranched C 1 -C 4 -alkyl radical;

A 1 is selected from the group consisting of H, a non-substituted halogen-substituted, branched or unbranched C 1 -C 20 -alkyl radical, a non-substituted or halogen-substituted C 5 -C 8 -cycloalkyl radical, a branched or unbranched hydroxylated C 1 -C 20 -alkyl radical;

A 2 is selected from the group consisting of H, a non-substituted halogen-substituted, branched or unbranched C 1 -C 20 -alkyl radical, a non-substituted or halogen-substituted C 5 -C 8 -cycloalkyl radical, a branched or unbranched hydroxylated C 1 -C 20 -alkyl radical;

A 3 is selected from the group consisting of H, a non-substituted halogen-substituted, branched or unbranched C 1 -C 20 -alkyl radical, a non-substituted or halogen-substituted C 5 -C 8 -cycloalkyl radical, a branched or unbranched hydroxylated C 1 -C 20 -alkyl radical;

(b) heating the solution to at least 35° C.; and

(c) recovering a compound according to Formula (2)

wherein

R 1x is selected from the group consisting of H, an unsubstituted or halogen-substituted, branched or unbranched C 1 -C 20 -alkyl radical, an unsubstituted or halogen-substituted C 5 -C 8 -cycloalkyl radical, an unsubstituted or halogen-substituted C 8 -C 10 -aryl radical or an unsubstituted or halogen-substituted, branched or unbranched C 7 -C 20 -aralkyl radical;

R 2x is either O or S,

R 3x is H or a branched or unbranched C 1 -C 4 -alkyl radical.

2. The process according to claim 1 , wherein the molar ratio of the compound according to Formula (1) to the acid is from 1:1 to 1:5.

3. The process according to claim 1 , wherein the solution is prepared by mixing at least one compound according to Formula (1) with the at least one solvent, followed by gradually adding the at least one acid.

4. The process according to claim 1 , wherein during step (b), the compound according to Formula (1) is dissolved in the solution.

5. The process according to claim 1 , wherein the cation in Formula (1) is selected from the group consisting of monoethanolamine, diethanolamine, triethanolamine, methylamine, dimethylamine, trimethylamine, ethyl amine, diethylamine, trimethylamine, diisopropylethylamine, and combinations thereof.

6. The process according to claim 1 , wherein the acid is selected from the group consisting of hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, HNO 3 , acetic acid, formic acid, and mixtures thereof.

7. The process according to claim 1 , wherein in step (b) the solution is heated to a temperature of between 35° C. and 80° C.

8. The process according to claim 1 , wherein the weight ratio of compound according to Formula (1) to the solvent is from 1:0.7 to 1:1.3.

9. The process according to claim 1 , wherein in step (b) the solution is heated for at least 30 minutes.

10. The process according to claim 1 , wherein step (c) comprises cooling the solution.

11. The process according to claim 1 , wherein R 2 and R 2x are both O.

12. The process according to claim 1 , wherein R 3 and R 3x are methyl and R 1 and R 1x are either cyclohexyl or 2,4,4-trimethylpentyl.

13. The process according to claim 1 , wherein the compound according to Formula (1) is selected from the group consisting of a monoethanolamine salt of 4-methyl-6-(2,4,4-trimethylpentyl) hydroxy-2-pyridone and a diethanolamine salt of 4-methyl-6-(2,4,4-trimethylpentyl)-1-hydroxy-2-pyridone.

14. The process according to claim 1 , wherein the compound according to Formula (2) is selected from the group consisting of 2-hydroxypyridine-1-oxide and 1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)-2(1H)-pyridone.

15. The process according to claim 1 , wherein the cation in Formula (1) is selected from the group consisting of monoethanolamine, diethanolamine, and combinations thereof.

16. The process according to claim 1 , wherein step (c) comprises pouring the solution onto ice, filtering off solid material, and subsequently drying the solid material.