Process for preparing dithiine-tetracarboximides

1. A process for preparing a compound of formula (I)

in which

R 1 and R 2 are identical or different and are hydrogen; C 1 -C 8 -alkyl which is optionally substituted with one or more halogen, —OR 3 , or —COR 4 ; C 3 -C 7 -cycloalkyl which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; or aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 , or sulphonylamino,

R 3 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkylcarbonyl, or aryl, wherein the aryl is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl,

R 4 is hydroxyl, C 1 -C 4 -alkyl, or C 1 -C 4 -alkoxy,

comprising:

(1) reacting succinic monoamides of formula (VI)

in which R is R 1 or R 2 with an excess of thionyl chloride, optionally in the presence of a diluent;

(2) removing thionyl chloride to form a product mixture; and

(3) adding an organic solvent to the product mixture and after a reaction time of between 5 minutes and 24 hours converting,

into a compound of formula (I).

2. The process according to claim 1 , wherein in (1), between 2 and 100 moles of thionyl chloride are used per mole of succinic monoamide of formula (VI).

3. The process according to claim 1 , wherein (1) is carried out without diluent.

4. The process according to claim 1 , wherein the organic solvent in (3) is at least partly miscible with water.

5. The process according to claim 1 , wherein the organic solvent in (3) is water, dimethyl sulphoxide, sulpholane, an alcohol, a hydrocarbon, an ester, an ether, a nitrile, a carboxylic acid, or mixtures thereof.

6. The process according to claim 1 , wherein (3) is carried out with heating.

7. A process for preparing a mixture comprising:

(1) a compound of formula (IX),

in which

R 1 and R 2 are identical or different and are hydrogen; C 1 -C 8 -alkyl which is optionally substituted with one or more halogen, —OR 3 , or —COR 4 ; C 3 -C 7 -cycloalkyl which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; or aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 , or sulphonylamino,

R 3 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkylcarbonyl, or is aryl, wherein the aryl is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl,

R 4 is hydroxyl, C 1 -C 4 -alkyl, or C 1 -C 4 -alkoxy,

n is 0, 1, or 2, and

(2) a compound of formula (VIII)

in which R is R 1 or R 2 and X is chlorine or hydroxyl,

comprising reacting a compound of formula (VI)

in which R is R 1 or R 2 with an excess of thionyl chloride, optionally in the presence of a diluent.

8. A compound of formula (IX),

in which

R 1 and R 2 are identical or different and are hydrogen; C 1 -C 8 -alkyl which is optionally substituted with one or more halogen, —OR 3 , or —COR 4 ; C 3 -C 7 -cycloalkyl which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; or aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 , or sulphonylamino,

R 3 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkylcarbonyl, or aryl, wherein the aryl is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl,

R 4 is hydroxyl, C 1 -C 4 -alkyl, or C 1 -C 4 alkoxy,

n is 0, 1, or 2.

9. A compound of formula (VIII)

in which

R is hydrogen; C 1 -C 8 -alkyl which is optionally substituted with one or more halogen, —OR 3 , or —COR 4 ; C 3 -C 7 -cycloalkyl which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; or aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 , or sulphonylamino,

R 3 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkylcarbonyl, or aryl, wherein the aryl is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl,

R 4 is hydroxyl, C 1 -C 4 -alkyl, or C 1 -C 4 -alkoxy;

X is chlorine or hydroxyl.

10. The process of claim 1 , wherein in (1), between 4 and 50 moles of thionyl chloride are used per mole of the succinic monoamide of formula (VI).

11. The process of claim 1 , wherein in (1), between 10 and 40 moles of thionyl chloride are used per mole of the succinic monoamide of formula (VI).

12. The process of claim 1 , wherein the organic solvent in (3) is selected from water, dimethyl sulphoxide, methanol, ethanol, propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, tertiary-butanol, 1-pentanol, cyclopentanol, cyclohexanol, ethylene glycol, ethylene glycol monomethyl ether, hexane, heptane, cyclohexane, methylcyclohexane, toluene, xylenes, mesitylene, chlorobenzene, dichlorobenzene, nitrobenzene, methyl acetate, ethyl acetate, formamide, N,N-dimethylformamide, dimethylacetamide, N-methylpyrrolidone, methyl tert-butyl ether, tetrahydrofuran, 1,4-dioxane, acetonitrile, propionitrile, butyronitrile, benzonitrile, acetone, methyl ethyl ketone, methyl isobutyl ketone, pinacolone, formic acid, acetic acid, propionic acid, or mixtures thereof.

13. The process of claim 1 , wherein the organic solvent in (3) is selected from water, methanol, ethanol, propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol, methyl acetate, tetrahydrofuran, 1,4-dioxane, acetonitrile, acetone, acetic acid, or mixtures thereof.

14. The process of claim 1 , wherein the succinic monoamide is N-methylsuccamide, N-butylsuccinamide, N-cyclohexylsuccinamide, or N-propylsuccinamide.

15. The process of claim 1 , wherein the compound of formula (I) is selected from:

2,6-dimethyl-1H,5H-[1,4]dithiino[2,3-c:5,6-c′]dipyrrole-1,3,5,7(2H,6H)-tetrone;

2,6-di-tert-butyl-1H,5H-[1,4]dithiino[2,3-c:5,6-c′]dipyrrole-1,3,5,7(2H,6H)-tetrone;

2,6-dicyclohexyl-1H,5H-[1,4]dithiino[2,3-c:5,6-c′]dipyrrole-1,3,5,7(2H,6H)-tetrone;

or

2,6-dipropyl-1H,5H-[1,4]dithiino[2,3-c:5,6-c′]dipyrrole-1,3,5,7(2H,6H)-tetrone.

16. The compound of claim 8 , selected from:

3,3′-trisulphane-1,3-diylbis(4-chloro-1-methyl-1H-pyrrole-2,5-dione);

3,3′-disulphanediylbis(4-chloro-1-methyl-1H-pyrrole-2,5-dione);

3,3′-disulphanediylbis(1-tert-butyl-4-chloro-1H-pyrrole-2,5-dione);

3,3′-trisulphane-1,3-diylbis(1-tert-butyl-4-chloro-1H-pyrrole-2,5-dione); or

3,3′-trisulphane-1,3-diylbis(4-chloro-1-cyclohexyl-1H-pyrrole-2,5-dione).

17. The process of claim 1 , wherein the thionyl chloride is removed by distillation.

18. The process of claim 1 , wherein (3) is carried out at a temperature between 30° C. and 130° C.

19. The process of claim 1 , wherein in (3) the reaction time is between 30 minutes and 12 hours.