Process for making monomenthyl esters
View Patent ↗A process for making monomenthyl esters of dicarboxylic acids is disclosed. Menthol reacts with a saturated, cyclic anhydride in the presence of a base catalyst under conditions effective to produce a mixture of mono- and bis-menthyl esters in which the molar ratio of mono- to bis-menthyl esters is enhanced compared with the ratio of esters produced in a similar uncatalyzed process.
1. A process which comprises reacting menthol with a saturated, cyclic anhydride in the presence of a base catalyst selected from the group consisting of alkali metal or alkaline earth metal salts, oxides, hydroxides, and mixtures thereof, under conditions effective to produce a mixture of mono- and bis-menthyl esters, wherein the molar ratio of cyclic anhydride to menthol is less than 2:1, and wherein the molar ratio of mono- to bis-menthyl esters is enhanced compared with a similar uncatalyzed process.
2. The process of claim 1 wherein the anhydride is selected from the group consisting of succinic anhydride, glutaric anhydride, and adipic anhydride.
3. The process of claim 1 wherein the catalyst is selected from the group consisting of alkali metal acetates, bicarbonates, carbonates, oxides, hydroxides, succinates, glutarates, and adipates.
4. The process of claim 1 performed at a temperature within the range of about 20° C. to about 150° C.
5. The process of claim 1 wherein the catalyst is used in an amount within the range of about 0.001 to about 10 wt. % based on the amount of menthol used.
6. The process of claim 1 wherein the molar ratio of mono- to bis-menthyl esters is at least 100% greater than the molar ratio obtained from the uncatalyzed process.
7. The process of claim 1 wherein the molar ratio of mono- to bis-menthyl esters is greater than 10.
8. The process of claim 1 wherein the monomenthyl ester has the structure:
in which n has a value from 2 to 4.