Method for preparation of alpha, beta-unsaturated cyclic ketones by dehydrogenation of secondary allylic cyclic alcohols
View Patent ↗A process for the manufacture of an alpha, beta-unsaturated cyclic ketone, such as carvone, comprises the dehydrogenation of a secondary allylic cyclic alcohol, such as carveol, in the presence of at least one metal carboxylate. The process can be performed in a batchwise or continuous mode. Examples of suitable metal carboxylates include magnesium stearate, calcium 2-ethylhexanoate, and zinc 2-ethylhexanoate.
1. A process for the manufacture of an alpha, beta-unsaturated cyclic ketone, comprising the dehydrogenation of a secondary allylic cyclic alcohol having the general structure:
in the presence of at least one metal carboxylate, in a reaction environment under conditions effective to provide an alpha, beta-unsaturated cyclic ketone of the general structure:
wherein R 1 and R 2 are independently selected from among straight chain or branched C 1 -C 5 alkyl groups, C 1 -C 5 alkenyl groups, or C 6 -C 10 aryl groups.
2. The process of claim 1 , wherein the secondary allylic cyclic alcohol is carveol and has the structure:
3. The process of claim 1 , wherein the alpha, beta-unsaturated cyclic ketone is carvone and has the structure:
4. The process of claim 1 , wherein the at least one metal is selected from Groups 2 and 12 of the periodic table.
5. The process of claim 1 , wherein the at least one metal is magnesium, calcium, zinc, or any combination thereof.
6. The process of claim 1 , wherein the at least one metal is zinc.
7. The process of claim 1 , wherein the at least one metal carboxylate is magnesium stearate, calcium 2-ethylhexanoate, zinc 2-ethylhexanoate or any combination thereof.
8. The process of claim 1 , wherein the at least one metal carboxylate is zinc 2-ethylhexanoate.
9. The process of claim 1 , wherein the reaction environment comprises at least one solvent.
10. The process of claim 9 , wherein the at least one solvent comprises an aliphatic hydrocarbon.
11. The process of claim 9 , wherein the at least one solvent comprises an ether.
12. The process of claim 9 , wherein the at least one solvent comprises cis-pinane, dodecane, pentadecane, mineral oil, diphenyl ether, tetraethylene glycol dimethyl ether or any combination thereof.
13. The process of claim 9 , wherein the at least one solvent is present in an amount of from about from 0.5 wt. % to about 400 wt. % based on the secondary alcohol.
14. The process of claim 1 , wherein the at least one metal carboxylate is present in an amount of from approximately 0.5% by weight to approximately 100% by weight relative to the secondary alcohol.
15. The process of claim 1 , wherein the conditions effective to provide an alpha, beta-unsaturated cyclic ketone comprise heating the reaction environment.
16. The process of claim 15 , wherein the reaction environment is heated to a temperature within the range of from approximately 210° C. to approximately 260° C.
17. The process of claim 1 , wherein the conditions effective to provide an alpha, beta-unsaturated cyclic ketone comprise maintaining the reaction environment at or below atmospheric pressure.
18. The process of claim 1 , wherein the condition effective to provide an alpha, beta-unsaturated cyclic ketone comprise refluxing the reaction environment.
19. The process of claim 1 , wherein the process is carried out in a batchwise mode.
20. The process of claim 19 , wherein the at least one metal carboxylate is present in an amount of 1-4 wt. % based on starting secondary alcohol.
21. The process of claim 19 , wherein the at least one metal carboxylate is present in an amount of 0.5-2 wt. % based on total reaction mixture.
22. The process of claim 1 , wherein the process is carried out in a continuous mode.
23. The process of claim 22 , wherein the at least one metal carboxylate is present in the reaction environment, based on throughput, of 0.01-1 g of secondary alcohol per 1 g catalyst per hour.
24. The process of claim 22 , wherein the alpha, beta-unsaturated cyclic ketone is continuously removed from the reaction environment.
25. The process of claim 1 , wherein the process further comprises removing water from the reaction environment.
26. The process of claim 1 , wherein the process further provides a beta, gamma-unsaturated cyclic ketone.
27. The process of claim 26 , wherein the beta, gamma-unsaturated cyclic ketone is spicatone.
28. The process of claim 26 , wherein the process further comprises an isomerization step to isomerize beta, gamma-unsaturated cyclic ketone to an alpha, beta-unsaturated cyclic ketone.
29. The process of claim 26 , wherein the isomerization step is performed thermally by heating beta, gamma-unsaturated cyclic ketone to a temperature in the range of from approximately 200° C. to approximately 240°.
30. The process of claim 26 , wherein the isomerization step is performed by treating beta, gamma-unsaturated cyclic ketone with a sodium hydroxide solution.