Search Results (19)

Novel lipophilic hydroxyalkyl esters were synthetized by Fischer esterification in good to excellent yields (60–96%) from a panel of hydroxyphenylacetic acids and increasing chain length (2 to 8 carbon atoms) α,ω-diols. The in vitro antioxidant activity of these compounds was evaluated by DPPH and ABTS assays. Hydroxybutyl esters and hydroxyphenylacetic acids were used as starting materials for the synthesis of novel lipophilic diesters (butyl diarylacetates) using Mitsunobu reaction. The final products were isolated in moderate to good yields (40–78%), and their structure–antioxidant activity relationships are discussed. Compounds bearing the catechol moiety on one of the two aromatic rings and high lipophilicity proved to be the strongest antioxidants and were selected for testing as antibacterials against Staphylococcus aureus and Escherichia coli, obtaining preliminary and promising results. Full article

A novel monomer, 9-bis[4-(2-hydroxyethoxy)phenyl]fluorene di(mercaptopropionate), with a highly refractive index, purity, and excellent UV-curable properties, is synthesized through an optimized Fischer esterification process, reacting 9,9-bis[4-(2-hydroxyethoxy)phenyl]fluorene with 3-mercaptopropionic acid. The structural characterization of this monomer is performed using Fourier-transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and liquid chromatography-mass spectrometry. The synthesis conditions are optimized using a design-of-experiments approach. UV-curable resins are obtained by incorporating the synthesized monomer as the thiol component. The effects of thiol content on the UV-curing behavior, refractive index, shrinkage, adhesion to the polyethylene terephthalate (PET) foil, and viscoelastic recovery are examined. The thermal properties are assessed using differential scanning calorimetry and thermogravimetric analysis. Field-emission scanning electron microscopy confirms the successful replication of the prism film. In edge-lit light-emitting diode (LED) backlight units, the prism film showed increased luminance with higher thiol monomer content in the UV-curable resin while maintaining stable color coordinates. This novel highly refractive index monomer can be utilized in luminance-enhancing prism films, thereby contributing to future innovations in the display film industry. Full article

Over the past 130 years, Fischer-Speier esterification has been established as the benchmark method for synthesizing esters from organic acids and alcohols. The reaction’s versatility, arising from the vast combinations of starting materials and the numerous catalytic alternatives to the traditional H₂SO₄, has maintained its relevance, with a steady flow of publications addressing new developments. This review highlights the most significant contributions to Fischer-Speier esterification over the past five years, with a particular emphasis on mechanistic advancements and innovative catalytic systems. Both homogeneous and heterogeneous catalytic approaches are discussed, including novel catalysts leveraging hydrogen-bonding interactions and systems offering fresh insights into specific reaction mechanisms and atypical methodologies. Some of these catalytic systems, as ionic liquids or sulfonated heterogeneous catalytic precursors, reached excellent yields (>90%), e.g., in the synthesis of fatty acids methyl esters. Also, classic catalysts such as H₂SO₄ and para-toluen sulfonic acid were optimized for quantitative conversions (e.g., in the esterification of trans-cinnamic acid with methanol). A consistent number of catalysts was studied with model substrates (as benzoic acid in combination with methanol, ethanol, and ethylene glycol), and new activation pathways were presented. Full article

The main goal of this work is to evaluate the ability of sulfonated carbon nanoparticles (SCNs) to induce photothermal catalysis of the biodiesel synthesis reaction (transesterification of natural triglycerides (TGs) with alcohols). Carbon nanoparticles (CNs) are produced by the carbonization of cross-linked resin nanoparticles (RNs). The RNs are produced by condensation of a phenol (resorcinol or natural tannin) with formaldehyde under ammonia catalysis (Stober method). The method produces nanoparticles, which are carbonized into carbon nanoparticles (CNs). The illumination of CNs increases the temperature proportionally (linear) to the nanoparticle concentration and exposure time (with saturation). Solid acid catalysts are made by heating in concentrated sulfuric acid (SEAr sulfonation). The application of either light or a catalyst (SCNs) (at 25 °C) induced low conversions (<10%) for the esterification reaction of acetic acid with bioethanol. In contrast, the illumination of the reaction medium containing SCNs induced high conversions (>75%). In the case of biodiesel synthesis (transesterification of sunflower oil with bioethanol), conversions greater than 40% were observed only when light and the catalyst (SCNs) were applied simultaneously. Therefore, it is possible to use sulfonated carbon nanoparticles as photothermally activated catalysts for Fischer esterification and triglyceride transesterification (biodiesel synthesis). Full article

Antimicrobial resistance has emerged as a significant danger to global health, and the need for more effective antimicrobial resistance (AMR) control has been highlighted. Cinnamic acid is abundant in plant products and is a potential starting material for further modification, focusing on the development of new antimicrobial compounds. In the following review, we describe the classification of critical antibacterial-guided reactions applied to the main skeleton structure of cinnamic acid derivatives over the last decade. Of all of the main parts of cinnamic acids, the phenyl ring and the carboxylic group significantly affect antibacterial activity. The results presented in the following review can provide valuable insights into considerable features in the organic modification of cinnamic acids related to antibacterial medication development and the food industry. Full article

Diisoamyl (1R,4S)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate (2) was prepared by reacting exo-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride (1) with isoamyl alcohol in the presence of a sulfuric acid catalyst under sonication conditions. Compound 2 was characterized by ¹H, ¹³C NMR, DEPT-135, infrared, and UV-vis spectroscopy. Gas chromatography–mass spectrometry, elemental analysis, and melting point determination were used to assess purity. The structure of compound 2 was also determined by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group P2₁/c (14) with cell values of a = 15.5647(3) Å, b = 12.8969(2) Å, c = 9.0873(2) Å; β= 99.3920(10)°. Full article

The development of photothermal catalysts for biodiesel synthesis reaction (transesterification) requires the production of light-absorbing nanoparticles functionalized with catalytic (acid) groups. Using Stöber method, it is possible to produce resorcinol/formaldehyde resin (RF) nanoparticles, which can be carbonized (pyrolysis in an inert atmosphere) and sulfonated. In this work, vegetable tannins are used as a replacement for synthetic resorcinol in the Stöber synthesis of resin (TF) nanoparticles. The nanoparticles are characterized using DLS, FESEM, TEM and N₂ adsorption-desorption isotherms. Both resin and carbon nanoparticles are sulfonated by reaction with concentrated sulfuric acid. The attachment of sulfonic groups is verified by FTIR and EDX. The number of sulfonic groups is measured by acid/base titration and TGA. All sulfonated nanoparticles show catalytic activities towards Fischer esterification of ethanoic acid with ethanol, and high (up to 70%) conversion is obtained. The conversion is lower with TF-based nanoparticles, but the turnover numbers are similar in the RF- and TF-based materials. Sulfonated carbon and resin nanoparticles show higher catalytic activity compared to commercial acidic catalysts (e.g., Nafion^®). Photothermal heating of carbon nanoparticles is observed. In Part II, sunflower oil transesterification, catalyzed by sulfonated nanoparticles, is observed. Photothermal catalysis of acetic acid esterification and sunflower oil transesterification is demonstrated. Full article

Cancer is a principal cause of death in the world, and providing a better quality of life and reducing mortality through effective pharmacological treatment remains a challenge. Among malignant tumor types, squamous cell carcinoma-esophageal cancer (EC) is usually located in the mouth, with approximately 90% located mainly on the tongue and floor of the mouth. Piplartine is an alkamide found in certain species of the genus Piper and presents many pharmacological properties including antitumor activity. In the present study, the cytotoxic potential of a collection of piplartine analogs against human oral SCC9 carcinoma cells was evaluated. The analogs were prepared via Fischer esterification reactions, alkyl and aryl halide esterification, and a coupling reaction with PyBOP using the natural compound 3,4,5-trimethoxybenzoic acid as a starting material. The products were structurally characterized using ¹H and ¹³C nuclear magnetic resonance, infrared spectroscopy, and high-resolution mass spectrometry for the unpublished compounds. The compound 4-methoxy-benzyl 3,4,5-trimethoxybenzoate (9) presented an IC₅₀ of 46.21 µM, high selectively (SI > 16), and caused apoptosis in SCC9 cancer cells. The molecular modeling study suggested a multi-target mechanism of action for the antitumor activity of compound 9 with CRM1 as the main target receptor. Full article

Eight gallic acid alkyl esters (1–8) were synthesized via Fischer esterification and evaluated for their trypanocidal and leishmanicidal activity using bloodstream forms of Trypanosoma brucei and promastigotes of Leishmania major. The general cytotoxicity of the esters was evaluated with human HL-60 cells. The compounds displayed moderate to good trypanocidal but zero to low leishmanicidal activity. Gallic acid esters with alkyl chains of three or four carbon atoms in linear arrangement (propyl (4), butyl (5), and isopentyl (6)) were found to be the most trypanocidal compounds with 50% growth inhibition values of ~3 μM. On the other hand, HL-60 cells were less susceptible to the compounds, thus, resulting in moderate selectivity indices (ratio of cytotoxic to trypanocidal activity) of >20 for the esters 4–6. Modeling studies combining molecular docking and molecular dynamics simulations suggest that the trypanocidal mechanism of action of gallic acid alkyl esters could be related to the inhibition of the T. brucei alternative oxidase. This suggestion is supported by the observation that trypanosomes became immobile within minutes when incubated with the esters in the presence of glycerol as the sole substrate. These results indicate that gallic acid alkyl esters are interesting compounds to be considered for further antitrypanosomal drug development. Full article

Pyrano [3,4-b]indol-1(9H)-ones and indolo [2,3-c]coumarins are important classes of heterocyclic compounds with versatile biological activities. Herein, we describe a straightforward and scalable synthesis of 3,6-dihydro-5H-pyrazolo [4′,3′:5,6]pyrano [3,4-b]indol-5-one, a pyrazolo-fused pyrano [3,4-b]indolone, via a three step approach including Fischer-indole synthesis and intramolecular esterification. The compound is fully characterized by means of ¹H and ¹³C NMR spectra, using direct and long-range heteronuclear correlation experiments (HMBC and HMQC). Full article

Fluorescent cellulose nanofibers (FCNFs), with a high yield, were prepared via one-pot hydrolysis and the grafting reaction of cellulose with thiazolipyridine carboxylic acid (TPCA). The hydrolysis and Fischer esterification of cellulose were conducted under microwave-hydrothermal conditions; meanwhile, TPCA formation was induced by the dehydration reaction between L-cysteine and citric acid. The effects of the reaction temperature and reaction time on the yield and performance of FCNF were investigated. The morphology and size, surface chemical property, crystal structure, thermostability, and fluorescent performance of FCNF were characterized. The results revealed that the yield of FCNF reached 73.2% under a microwave power of 500 W, reaction temperature of 110 °C, and reaction time of 5 h. The FCNF obtained presents a short rod-like morphology. The crystallinity of the FCNFs is 80%, and their thermal stability did not decline significantly. Additionally, the fluorescent performance of the FCNFs is excellent, which results in them having good sensitivity to chloride ions. The good fluorescent performance and significant responsiveness to chloride ions of FCNFs lead to them having broad prospects in bio-labeling, biosensing, information storage, chloride ion detection, among others. Full article

The title compound, propyl gallate (III), is an important substance popularly used in the food, cosmetic and pharmaceutical industries. Current chemical syntheses of this compound are based on the acylation supported by thionyl chloride, DIC/DMAP or Fischer esterification using a range of homogenous and heterogenous catalysts. In this paper, an efficient, green, straightforward, and economical method for synthesizing propyl gallate using potassium hydrogen sulfate, KHSO₄, as the heterogenous acidic catalyst has been developed for the first time. In addition, this paper provides a comprehensive spectral dataset for the title compound, especially the new data on DEPT and 2D NMR (HSQC and HMBC) spectra which are not currently available in the literature. Full article

An effective method for levulinic acid esters synthesis by the enzymatic Fischer esterification of levulinic acid using a lipase B from Candida antarctica (CALB) immobilized on the advanced material consisting of multi-wall carbon nanotubes (MWCNTs) and a hydrophobic polymer—polytetrafluoroethylene (Teflon, PTFE)—as a heterogeneous biocatalyst, was developed. An active phase of the biocatalyst was obtained by immobilization via interfacial activation on the surface of the hybrid material MWCNTs/PTFE (immobilization yield: 6%, activity of CALB: 5000 U∙L∙kg⁻¹, enzyme loading: 22.5 wt.%). The catalytic activity of the obtained biocatalyst and the effects of the selected reaction parameters, including the agitation speed, the amount of PTFE in the CALB/MWCNT-PTFE biocatalyst, the amount of CALB/MWCNT-PTFE, the type of organic solvent, n-butanol excess, were tested in the esterification of levulinic acid by n-butanol. The results showed that the use of a two-fold excess of levulinic acid to n-butanol, 22.5 wt.% of CALB on MWCNT-PTFE (0.10 wt.%) and cyclohexane as a solvent at 20 °C allowed one to obtain n-butyl levulinate with a high yield (99%) and selectivity (>99%) after 45 min. The catalyst retained its activity and stability after three cycles, and then started to lose activity until dropping to a 69% yield of ester in the sixth reaction run. The presented method has opened the new possibilities for environmentally friendly synthesis of levulinate esters. Full article

In this work, a sustainable chemical process was developed through the Fischer esterification of Protobind^® lignin, a wheat straw soda lignin, and phloretic acid, a naturally occurring phenolic acid. It aimed at increasing the reactivity of lignin by enhancing the number of unsubstituted phenolic groups via a green and solvent-free chemical pathway. The structural features of the technical and esterified lignins were characterized by complementary spectroscopic techniques, including ¹H, ¹³C, ³¹P, and two-dimensional analysis. A substantial increase in p-hydroxyphenyl units was measured (+64%, corresponding to an increase of +1.3 mmol g⁻¹). A full factorial design of the experiment was employed to quantify the impact of critical variables on the conversion yield. The subsequent statistical analysis suggested that the initial molar ratio between the two precursors was the factor predominating the yield of the reaction. Hansen solubility parameters of both the technical and esterified lignins were determined by solubility assays in multiple solvents, evidencing their high solubility in common organic solvents. The esterified lignin demonstrated a better thermal stability as the onset of thermal degradation shifted from 157 to 220 °C, concomitantly to the shift of the glass transition from 92 to 112 °C. In conclusion, the esterified lignin showed potential for being used as sustainable building blocks for composite and thermoset applications. Full article

This study evaluates a novel handheld sensor technology coupled with pattern recognition to provide real-time screening of several soybean traits for breeders and farmers, namely protein and fat quality. We developed predictive regression models that can quantify soybean quality traits based on near-infrared (NIR) spectra acquired by a handheld instrument. This system has been utilized to measure crude protein, essential amino acids (lysine, threonine, methionine, tryptophan, and cysteine) composition, total fat, the profile of major fatty acids, and moisture content in soybeans (n = 107), and soy products including soy isolates, soy concentrates, and soy supplement drink powders (n = 15). Reference quantification of crude protein content used the Dumas combustion method (AOAC 992.23), and individual amino acids were determined using traditional protein hydrolysis (AOAC 982.30). Fat and moisture content were determined by Soxhlet (AOAC 945.16) and Karl Fischer methods, respectively, and fatty acid composition via gas chromatography-fatty acid methyl esterification. Predictive models were built and validated using ground soybean and soy products. Robust partial least square regression (PLSR) models predicted all measured quality parameters with high integrity of fit (R_Pre ≥ 0.92), low root mean square error of prediction (0.02–3.07%), and high predictive performance (RPD range 2.4–8.8, RER range 7.5–29.2). Our study demonstrated that a handheld NIR sensor can supplant expensive laboratory testing that can take weeks to produce results and provide soybean breeders and growers with a rapid, accurate, and non-destructive tool that can be used in the field for real-time analysis of soybeans to facilitate faster decision-making. Full article