Process for the oxidation of secondary amines into the corresponding nitroxides

1. A process for the preparation of secondary nitroxide radicals from their corresponding secondary amines by oxidation with an organic peracid, comprising the steps of:

a) forming a reaction mixture by adding to a reaction vessel a secondary amine and in one batch either

an amount of water together with solid NaHCO 3 , KHCO 3 , or a mixture thereof; or

an aqueous slurry of NaHCO 3 , KHCO 3 , or a mixture thereof; and

b) dosing a peracid to the reaction mixture in an amount of 1.0 to 2.5 mol per mol of secondary amine.

2. The process according to claim 1 further comprising adding an organic solvent immiscible with water to the reaction mixture prior to dosing said peracid.

3. The process according to claim 1 wherein the peracid is peracetic acid.

4. The process according to claim 1 wherein the NaHCO 3 , KHCO 3 , or mixture thereof is added in an amount of from 0.1 to 1.5 equivalents per 1 equivalent of all acids present.

5. The process according to claim 1 wherein the reaction temperature is between 0° C. and 40° C.

6. The process according to claim 1 wherein dosing the peracid is carried out from 10 minutes to 5 hours.

7. The process according to claim 1 wherein the nitroxide radical is of formula (I)

wherein

R p and R q are independently tertiary bound C 4 -C 28 alkyl groups or C 3 -C 17 secondary bound alkyl groups which are unsubstituted or by one or more electron withdrawing groups or by phenyl; or

R p and R q together form a 5, 6 or 7 membered heterocyclic ring which is substituted at least by 4 C 1 -C 4 alkyl groups and which may be interrupted by a further nitrogen or oxygen atom.

8. The process according to claim 1 wherein the nitroxide radical is within a structural element of formula (X)

wherein

G 1 , G 2 , G 3 , G 4 are independently C 1 -C 6 alkyl; or

G 1 and G 2 or G 3 and G 4 , or G 1 and G 2 and G 3 and G 4 together form a C 5 -C 12 cycloalkyl group;

*denotes a valence; and

G 5 , G 6 independently are H or C 1 -C 6 alkyl.

9. A process for the preparation of secondary nitroxide radicals from their corresponding secondary amines by oxidation with an organic peracid, said process comprising the steps of:

a) forming a reaction mixture by adding to a reaction vessel a secondary amine and in one batch solid NaHCO 3 , KHCO 3 , or a mixture thereof; and

b) dosing a peracid to the reaction mixture in an amount of 1.0 to 2.5 mol per mol of secondary amine;

wherein said forming and said dosing are done in the absence of water.

10. The process according to claim 9 further comprising adding an organic solvent immiscible with water to the reaction mixture prior to dosing said peracid.

11. The process according to claim 9 wherein the peracid is peracetic acid.

12. The process according to claim 9 wherein the NaHCO 3 , KHCO 3 , or mixture thereof is added in an amount of from 0.1 to 1.5 equivalents per 1 equivalent of all acids present.

13. The process according to claim 9 wherein the reaction temperature is between 0° C. and 40° C.

14. The process according to claim 9 wherein dosing the peracid is carried out from 10 minutes to 5 hours.

15. The process according to claim 8 , wherein the radical is of formula (X):

wherein

G 1 , G 2 , G 3 , G 4 are independently C 1 -C 6 -alkyl;

*denotes a valence; and

G 5 , G 6 independently are H or C 1 -C 6 -alkyl;

from its corresponding secondary amine by oxidation with an organic peracid, comprising the steps

a) forming a reaction mixture by adding to a reaction vessel a secondary amine, optionally together with an organic solvent and in one batch either an amount of water together with solid NaHCO 3 , KHCO 3 , or a mixture thereof or an aqueous slurry of NaHCO 3 , KHCO 3 , or a mixture thereof;

b) dosing a peracid under stirring to the reaction mixture in an amount of 1.0 to 2.5 mol per mol of secondary amine; and

c) isolating the organic phase.

16. The process according to claim 1 , wherein the secondary nitroxide radicals are selected from secondary nitroxide radicals of formula (I):

wherein

R p and R q together form a heterocyclic ring which is substituted at least by four C 1 -C 4 -alkyl groups or

wherein

G 5 and G 6 are independently hydrogen or C 1 -C 4 -alkyl, and

G 1 and G 3 are methyl and G 2 and G 4 are ethyl or propyl or G 1 and G 2 are methyl and G 3 and G 4 are ethyl or propyl, or

17. A process according to claim 1 , wherein the secondary nitroxide radical is chosen from:

2,6-diethyl-2,3,6-trimethyl-piperidine-4-one;

2,6-diethyl-2,3,6-trimethyl-piperidine;

2,2,6,6-tetramethylpiperidin-4-one; and

octadecanoic acid 3,8,10-triethyl-7,8,10-trimethyl-1,5-dioxa-9-aza-spiro[5.5]undec-3-ylmethyl ester.