Lipophilic antioxidant dodecyl caffeate preparation by the esterification of caffeic acid with dodecanol using ionic liquid [Hnmp]HSO4 as a catalyst

Synthesis of lipophilic antioxidant tyrosol laurate using imidazolium ionic liquid [Bmim]HSO4 as a catalyst

Tyrosol is a natural phenolic compound with potent antioxidant properties in the field of food manufacturing. However, the low lipophilicity of tyrosol limited its application. Therefore, the construction of tyrosol laurate (Tyr-L) could effectively overcome the limitations of tyrosol. In this work, four ionic liquids (ILs) were applied for TYr-L preparation. Among them, the 1-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]HSO4) showed the best catalytic performance. The maximum TYr-L yield was achieved (94.24 ± 1.23 %) under the optimal conditions (reaction temperature 119 °C, substrate ratio 1:6.7, IL dosage 9.2 %, and reaction time 12 h). The kinetic and thermodynamic parameters were also evaluated and it was found that Ea, ΔH, ΔS, and ΔG were 80.81 kJ·mol-1, 77.63 kJ·mol-1, -82.08 J·(mol·K)-1, and 109.89 kJ·mol-1, respectively. The acidic [Bmim]HSO4 demonstrated excellent reusability and stability, even after 6 cycles. Furthermore, TYr-L showed superior ABTS radical scavenging ability, which could be further applied in various industrial processes.

Lipophilic alkyl caffeate synthesis using a novel green binuclear ionic liquid 1,1-bis(2-pyrrolidinone) sulfate ([C3(Hnhp)2][HSO4]2) catalyst

Caffeic acid (CA), as a potential green antioxidant, plays an important role in food processing. However, the low liposolubility of CA limits its applications. To overcome this issue, CA is normally modified by introducing a lipophilic group, such as alkyl alcohols, resulting in the formation of alkyl caffeate, which can significantly enhance the liposolubility of CA. In this study, a binuclear ionic liquid, 1,1-bis(2-pyrrolidinone) sulfate ([C3(Hnhp)2][HSO4]2), is successfully synthesized and characterized by FT-IR and 1H NMR. The physico-chemical properties of [C3(Hnhp)2][HSO4]2, including the density, viscosity, thermal stability and Brønsted acidity, were analyzed. As a novel catalyst for the esterification of CA with model dodecanol, its catalytic performance was investigated and optimized by response surface methodology. Under the optimal conditions, a 95.42 ± 1.01% yield of dodecanol caffeate was achieved. Moreover, the [C3(Hnhp)2][HSO4]2 exhibits excellent stability and reusability, making it a highly promising catalyst for the synthesis of various lipophilic alkyl caffeates.