Process for preparing terpinene-4-ol

Abstract

The present invention relates to a process for preparing terpinene-4-ol from limonene-4-ol via a hydrogenation reaction in the presence of a nickel catalyst.

Claims

1. A process for preparing terpinene-4-ol of formula (II) ##STR00006## said process comprising contacting limonene-4-ol of formula (I) ##STR00007## with hydrogen in the presence of at least one nickel catalyst and at least one inert organic solvent selected from carboxylic acid esters.

2. The process of claim 1, wherein the nickel catalyst comprises Raney nickel.

3. The process of claim 1, wherein the carboxylic acid ester is selected from esters of the general formula R.sup.1COOR.sup.2 wherein R.sup.1 is hydrogen or selected from the group consisting of C.sub.1-C.sub.4-alkyl, C.sub.3-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl and C.sub.6-C.sub.10-aryl-C.sub.1-C.sub.4-alkyl and R.sup.2 is selected from the group consisting of C.sub.1-C.sub.4-alkyl, C.sub.3-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl and C.sub.6-C.sub.10-aryl-C.sub.1-C.sub.4-alkyl, each of the aforementioned groups optionally being substituted with one or more substituents selected from C.sub.1-C.sub.4-alkoxy.

4. The process of claim 1, wherein the carboxylic acid ester is selected from C.sub.1-C.sub.4-alkyl acetates.

5. The process of claim 1, wherein the carboxylic acid ester is ethyl acetate.

6. The process of claim 1, wherein the temperature is from 35 to 70 C.

7. The process of claim 1, wherein the hydrogen overpressure is from 10 mbar to 3 bar.

8. The process of claim 1, wherein limonene-4-ol of formula (I) is prepared by isomerization of terpinolene epoxide of the formula (III) ##STR00008##

9. The process of claim 8, wherein terpinolene epoxide of the formula (III) is further subjected to hydrogenation.

10. The process of claim 8, wherein the isomerization and/or hydrogenation are carried out in the presence of at least one copper catalyst.

11. The process claim 8, wherein the isomerization and/or hydrogenation are carried out in the presence of at least one inert organic solvent selected from carboxylic acid esters.

12. The process of claim 11, wherein a mixture comprising limonene-4-ol of the formula (I), terpinene-4-ol of the formula (II) and the at least one inert organic solvent selected from carboxylic acid esters is obtained.

13. The process of claim 1, wherein terpinene-4-ol of the formula (II) is further converted into ()-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof.

Description

EXAMPLE 1

(1) 6 g (0.102 mol) Raney-nickel (previously washed with ethanol and ethyl acetate) and 71 g ethyl acetate were placed in the reaction vessel. 318.7 g of a solution containing 27.93 w/w % limonene-4-ol (0.5848 mol) and 6.07 w/w % terpinene-4-ol (0.1254 mol) in ethyl acetate were added. The reactor was purged with nitrogen and hydrogen (very slow stirring). Then reaction mixture was pressurized with 100 mbar H.sub.2 under vigorous stirring and heated to 50 C. The temperature of the reaction mixture was held between 50 C. and 58 C. with cooling. Hydrogen adsorption was competed after 2 h. Then reaction mixture was cooled to 25 C. and the pressure was released. The catalyst was filtered off through a layer of diatomaceous earth. The remaining catalyst was washed with ethyl acetate. Filtrate and wash ethyl acetate were combined and ethyl acetate was distilled off at reduced pressure (distillation residue: 145.8 g). Quantitative gas chromatography (GC) (GC with internal standard) of the distillation residue showed a terpinene-4-ol concentration of 69.2% and 0% for limonene-4-ol. This corresponds to a yield of 90.4% for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol). Additional terpinene-4-ol was found in the distillate (1.35% yield). The total yield for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol) was 91.95%.

EXAMPLE 2

(2) Another hydrogenation experiment was performed under the same reaction conditions as in Example 1 but starting with 629.9 g of a solution containing 11.81 w/w % limonene-4-ol (0.4888 mol) and 2.53 w/w % terpinene-4-ol (0.1033 mol). 113.7 g of distillation residue were obtained. Quantitative GC (GC with internal standard) of the distillation residue showed a terpinene-4-ol concentration of 75.24% and 0% for limonene-4-ol. This corresponds to a yield of 93.85% for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol).

EXAMPLE 3

(3) 16.7 g Raney-nickel (water wet, 34% water; 0.188 mol) were purged in the reaction vessel with 5 g of water. 1297 g of a solution containing 32.0 w/w % limonene-4-ol (2.728 mol) and 7.1 w/w % terpinene-4-ol (0.60 mol) in ethyl acetate were added. The reactor was purged with nitrogen and hydrogen (very slow stirring). Then reaction mixture was pressurized with 100 mbar H.sub.2 under vigorous stirring and heated to 50 C. The temperature of the reaction mixture was held at 50 C. with cooling. Hydrogen adsorption was completed after 5 h. Then reaction mixture was cooled to 25 C. and the pressure was released. The catalyst was filtered off through a filter cloth. The remaining catalyst was washed with ethyl acetate. Filtrate and wash ethyl acetate were combined and ethyl acetate was distilled off at reduced pressure (distillation residue: 854.6 g). Quantitative gas chromatography (GC) (GC with internal standard) of the distillation residue showed a terpinene-4-ol concentration of 58.5% and 0% for limonene-4-ol. This corresponds to a yield of 96.76% for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol). Additional terpinene-4-ol was found in the distillate (1.04% yield). The total yield for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol) was 97.8%.

COMPARATIVE EXAMPLE 1

(4) 16.7 g Raney-nickel (water wet, 34% water; 0.188 mol) were purged in the reaction vessel with 5 g of water. 1297 g of a solution containing 31.8 w/w % limonene-4-ol (2.712 mol) and 7.0 w/w % terpinene-4-ol (0.59 mol) in ethanol were added. The reactor was purged with nitrogen and hydrogen (very slow stirring). Then reaction mixture was pressurized with 100 mbar H.sub.2 under vigorous stirring and heated to 50 C. The temperature of the reaction mixture was held at 50 C. with cooling. Hydrogen adsorption was completed after 7.5 h. Then reaction mixture was cooled to 25 C. and the pressure was released. The catalyst was filtered off through a filter cloth. The remaining catalyst was washed with ethanol. Filtrate and wash ethanol were combined and ethanol was distilled off at reduced pressure (distillation residue: 802.5 g). Quantitative gas chromatography (GC) (GC with internal standard) of the distillation residue showed a terpinene-4-ol concentration of 59.5% and 0% for limonene-4-ol. This corresponds to a yield of 92.41% for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol). Additional terpinene-4-ol was found in the distillate (3.05% yield). The total yield for terpinene-4-ol (referred to the limonene-4-ol in the starting mixture, without the pre-existing terpinene-4-ol) was 95.46%.

(5) The results of Example 3 and Comparative Example 1 demonstrate that the use of a carboxylic acid ester (i.e. ethyl acetate) as reaction solvent according to this invention gives a higher yield of terpinene-4-ol at a shorter reaction time (yield: 97.8%, reaction time: 5 h) as compared to the known use of ethanol (yield: 95.46%, reaction time: 7.5 h). The improvement of 2.34% in the yield at an even shorter reaction time is significant in view of the fact that the process of this invention is intended for the production of terpinene-4-ol on a large industrial scale.