Synthesis of Lipophilic Caffeoyl Alkyl Ester Using a Novel Natural Deep Eutectic Solvent

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.

Catalytic Routes to Produce Polyphenolic Esters (PEs) from Biomass Feedstocks

Polyphenolic esters (PEs) are valuable chemical compounds that display a wide spectrum of activities (e.g., anti-oxidative effects). As a result, their production through catalytic routes is an attractive field of research. The present review aims to discuss recent studies from the literature regarding the catalytic production of PEs from biomass feedstocks, namely, naturally occurred polyphenolic compounds. Several synthetic approaches are reported in the literature, mainly bio-catalysis and to a lesser extent acid catalysis. Immobilized lipases (e.g., Novozym 435) are the preferred enzymes thanks to their high reactivity, selectivity and reusability. Acid catalysis is principally investigated for the esterification of polyphenolic acids with fatty alcohols and/or glycerol, using both homogeneous (p-toluensulfonic acid, sulfonic acid and ionic liquids) and heterogeneous (strongly acidic cation exchange resins) catalysts. Based on the reviewed publications, we propose some suggestions to improve the synthesis of PEs with the aim of increasing the greenness of the overall production process. In fact, much more attention should be paid to the use of new and efficient acid catalysts and their reuse for multiple reaction cycles.

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

Caffeic acid (CA) is widely found in nature, and has a broad spectrum of biological activities. However, the low hydrophilicity and lipophilicity of CA limited its application. Dodecyl caffeate (DC) is the lipophilic ester of caffeic acid (CA), and also has high antioxidant activity. In this work, CA, used as a substrate, and three ionic liquids with different acidities and H₂SO₄ were used as economic catalysts for DC preparation. The effects of variables on DC yield were investigated and optimized by response surface methodology (RSM). And the kinetic and thermodynamic parameters of the esterification of CA and dodecanol were evaluated. Results showed that lipophilic DC was successfully synthesized using ionic liquid ([Hnmp]HSO₄) as a catalyst. And the optimal conditions by RSM were substrate ratio of 10.2 : 1, IL dosage of 9.8% at 87 °C for 118 min. Under the optional conditions, the maximum DC yield was 94.67 ± 1.32%. The k₀, E_a, ΔH, ΔS, and ΔG were 7.18 × 10⁷ mol (L min)⁻¹, 65.77 kJ mol⁻¹, 63.10 kJ (mol K)⁻¹, −103.80 J (mol K)⁻¹, and 99.78 kJ mol⁻¹ at 363 K, respectively. DC prepared in this work showed a good DPPH radical scavenging activity, which indicated that DC can be used as a potential antioxidant in food and cosmetics.

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

Enhancement of the hydrophilic feruloyl glycerol synthesis using A-35 as a catalyst and its functional characteristics

Feruloyl glycerol (FG) is the hydrophilic ester of ferulic acid (FA), which has a high solubility in water and a strong ability to resist ultraviolet (UV) radiation. In this work, several solid acids were used as novel economical catalysts and FA was used as a cheap substrate for FG preparation. The effects of reaction variables on the esterification of FA with glycerol were investigated and optimized by response surface methodology (RSM). Results showed that a cheap solid acid cation exchange resin A-35 showed the best performance for esterification. The reaction conditions were optimized by RSM as follows: 15 : 1 (glycerol/FA) substrate molar ratio and 14% catalyst loading at 90 °C for 7 h. The maximum FG yield (98.50 ± 0.58%) was achieved under the optimized conditions. The activation energy of the esterification was 53.71 kJ mol^-1. The results of UV absorbance showed that FG had good anti-UV activity and photostability, which can be used as a potential antioxidant and UV absorber in food and sunscreen products.

Choline Chloride-Based DES as Solvents/Catalysts/Chemical Donors in Pharmaceutical Synthesis

DES are mixtures of two or more compounds, able to form liquids upon mixing, with lower freezing points when compared to the individual constituents (eutectic mixtures). This attitude is due to the specific hydrogen-bond interactions network between the components of the mixture. A notable characteristic of DES is the possibility to develop tailor-made mixtures by changing the components ratios or a limited water dilution, for special applications, making them attractive for pharmaceutical purposes. In this review, we focused our attention on application of ChCl-based DES in the synthesis of pharmaceutical compounds. In this context, these eutectic mixtures can be used as solvents, solvents/catalysts, or as chemical donors and we explored some representative examples in recent literature of such applications.

Lipase-catalysed synthesis of mono- and di-acyl esters of glyceryl caffeate in propylene carbonate and their antioxidant properties in tuna oil

Development of new non-toxic antioxidants with diverse hydrophobic properties is important due to growing concerns about the toxicity of artificial oil-soluble antioxidants, the comparatively low effectiveness of natural options, and the complex role hydrophobicity plays in antioxidant effectiveness. Using caffeic acid, a naturally occurring phenolic acid with potent antioxidant activity, a range of glyceryl caffeate esters (decanoate and palmitate) were prepared using lipase-catalysed esterification reactions. Glyceryl-1-caffeate (GC) was prepared from ethyl caffeate and glycerol (acting as both the solvent and the substrate), catalysed by immobilised Candida Antarctica lipase B (Novozym-435) at 80 °C under vacuum. Esterification of GC with decanoic acid using immobilised Thermomyces lanuginosus lipase (TLIM) or Novozym-435 was found to be selective towards mono-acylated or di-acylated products, respectively. The reaction was performed in an unconventional solvent, propylene carbonate (PC), which has many of the attributes of a green solvent. Product conversions in PC were comparable to the best performing conventional solvents. In contrast to conventional volatile solvents, the low volatility of PC allowed the reaction to be performed under vacuum, without the need for molecular sieves for removal of water produced during the reaction. Diisopropyl ether was effective at extracting the more lipophilic products from PC. Both the lipase (Novozym-435) and PC were reused four times with only a small loss in conversion efficiency. Glyceryl caffeate esters performed much better than α-tocopherol at protecting bulk tuna oil from oxidation (analysed using Rancimat). A comparison of glyceryl caffeate esters (decanoate/palmitate and mono-/di-acylated) showed that their antioxidant effectiveness in bulk tuna oil was not affected by chain-length, but compounds containing only one fatty ester were slightly more effective than those containing two fatty esters.