Synthesis And Thermal Stability Of Three Menthol Esters

Menthol ester is an important component of flavors,which is mainly produced by esterification of menthol with aromatic acids and fatty acids.It is a very important perfume and pharmaceutical intermediates.It can be used as natural or non-natural drug precursors,as well as for the synthesis of compounds with biological activity.The synthesis of menthol esters and their derivatives has attracted much attention.In this paper,menthol syringate,menthol vanillate and menthol veratrate were synthesized.The synthesis route was optimized and the corresponding structures were characterized by IR,UV,GC-MS and NMR.Finally,the thermal stability of menthol ester was studied.The synthetic route of menthol syringate was as follows: Syringic acid was synthesized from eugenol aldehyde in concentrated sulfuric acid at 100? for 3h in water with yield of85.1%.Acetylsyringic acid was synthesized by the reaction of syringic acid with triethylamine as catalyst in acetic anhydride at 50? for 5h with yield of 95.4%.Then,using acetylsyringic acid and menthol as raw materials,4-dimethylaminopyridine as catalyst,N,N'-dicyclohexylcarbodiimide as absorbent,menthol acetylsyringate was synthesized from dichloroethane at room temperature for 5h in yield of 77.8%.Finally,menthol syringate was synthesized from menthol acetylsyringate by adding sodium metal and reacting in methanol for 2h with yield of 99.1%.The synthetic route of menthol vanillate was as follows: vanillin was used as raw material and potassium permanganate as catalyst to react in water at 40? for 1.5h to produce vanillic acid with yield of 81.3%.Acetylvanillic acid was synthesized from vanillic acid with1.3 times triethylamine as catalyst in acetic anhydride at 60? for 5h with yield of 96.5%.Then,acetylvanillic acid and menthol were used as raw materials,4-dimethylaminopyridine as catalyst,N,N'-dicyclohexylcarbodiimide as absorbent,and menthol acetylvanillate was synthesized from dichloroethane at room temperature for 5h with yield of 76.2%.Finally,menthol vanillate was synthesized from menthol acetylvanillate by adding sodium metal and reacting in methanol for 2h with yield of 98.9%.The synthetic route of menthol veratrate is: using vanillin as raw material,dimethyl sulfate as catalyst,reacting in 20% sodium hydroxide boiling water solution for 1.5h to produce veratraldehyde with yield of 83.3%.Then veratraldehyde was used as raw material and potassium permanganate was used as catalyst to react in water at 20? for 4h to produce veratric acid with yield of 96.8%.Finally,menthol veratrate was synthesized from resveratric acid and menthol,using 4-dimethylaminopyridine as catalyst,N,N'-dicyclohexylcarbodiimideas absorbent,and reacted in dichloroethane at room temperature for 5h with yield of 89.1%.TG-DTG-DSC thermogravimetric analysis of three kinds of menthol esters was carried out at 20-600? in air atmosphere.The main weightlessness zones of menthol syringate,menthol vanillate and menthol veratrate were respectively as follows: 215.3-345.4?,215.4-356.9? and 150.1-311.4?.The temperatures at 50% weightlessness are 308.5?,313.1? and 252.4?.The temperatures at the fastest weightlessness rate are 268.6?,328.5? and 289.7?.So it can be judged that the thermal stability of three menthol esters is good.In this thesis,the route of synthesizing menthol ester with aromatic acid containing phenolic hydroxyl group and phenolic methoxy group was discussed,and the method of synthesizing menthol ester containing phenolic hydroxyl group and phenolic methoxy group was preliminarily mastered.Its research laid the foundation for the application of menthol esters in flavors and pharmaceuticals.