Phenolic acid with catechol structure(eg. Caffeic acid) has strong antioxidant activity. However, phenolic acid exhibits low solubility and stability in hydrophobic systems, which limits its application. Therefore, combining phenolic acid with some fat-soluble molecules can not only keep its antioxidant activity and improve its lipophicity but also expand the scope of its application. This article studied the synthesis of propyl caffeate and hexanol ester of dihydrocaffeic acid using inexpensive p-toluenesulfonic acid as catalyst, the factors of substrate molar ratio、reaction temperature、catalyst loading、the amount of molecule sieves and water content in this system which influenced the esterification of caffeic acid and dihydrocaffeic acid were investigated. Acidic ionic liquid as a kind of green solvent received much attention in many fields. So, this article also studied the synthesis of propyl caffeate using acidic ionic liquid as catalyst, the factors of kinds of acidic ionic liquid、substrate molar ratio、reaction temperature、catalyst loading、the amount of molecule sieves and so on which influenced the esterification of caffeic acid were investigated. Based on the previous reaction conditions, a series of propyl phenolic ester were synthesized, the relationship between antioxidant activity and molecule structure was also studied.Using inexpensive p-toluenesulfonic acid as catalyst, propyl caffeate was synthesized. The highest conversion(97.64±0.98%) of caffeic acid and the highest yield(95.98±1.23%) of propyl caffeate were achieved under the optimum conditions as follows: molar ratio of caffeic acid to propanol was 1:10, reaction temperature was 90℃, the amount of catalyst was 0.1%, the amount of molecular sieve was 300mg/m L. The yield of propyl caffeate(white powder) was 90% isolated by column chromatography.Using acidic ionic liquid as catalyst, propyl caffeate was synthesized. The highest conversion(98.35±0.21%) of caffeic acid and the highest yield(97.87±0.33%) of propyl caffeate were obtained under the optimum conditions as follows: the optimal catalyst was [BSO3HMIM]TS, the molar ratio of caffeic acid to propanol was 1:20, reaction temperature was 90℃, the amount of catalyst was 40%(calculated by the total quality of reactant), additional molecular sieve was not needed. In addition, the reaction system can conduct efficiently in the condition of water content below 5%.Hexanol ester of dihydrocaffeic acid was synthesized using p-toluenesulfonic acid as catalyst. The highest conversion(99.38±0.11%) and the highest yield(99.21±0.31%) was acquired under the the optimum conditions as follows: the amount of catalyst was 1%(calculated by the total quality of reactant), the molar ratio of dihydrocaffeic acid to hexanol was 1:30, reaction temperature was 80℃, additional molecular sieve was not needed.Based on the previous reaction conditions, a series of propyl phenolic ester were synthesized, the relationship between antioxidant activity and molecule structure was also studied. The results showed that phenolic acid which has catechol structure and double bond connected with benzene ring had more strong antioxidant activity. At the same time, the antioxidant activity of propyl phenolic ester and phenolic acid was not the same due to the cut-off effect. |