Direct dehydrative esterification of alcohols and carboxylic acids with a macroporous polymeric acid catalyst

Highly efficient esterification of carboxylic acids with O-H nucleophiles through acid/iodide cooperative catalysis

The esterification of carboxylic acids is an important reaction for preparing esters which find wide applications in various research fields. In this manuscript, we report an acid/iodide cooperative catalytic method which enables highly efficient esterification of carboxylic acids with a wide range of equivalent O-H nucleophiles including both alcohols and weak nucleophilic phenols. Under the reaction conditions, both aromatic and aliphatic carboxylic acids including those bearing functional groups work well, furnishing the corresponding esters in good to high yields. Moreover, this reaction is scalable and applicable to the modification of bioactive molecules. These results demonstrate the synthetic value of this new reaction in organic synthesis.

Microwave Assisted Esterification of Aryl/Alkyl Acids Catalyzed by N-Fluorobenzenesulfonimide

The susceptibility of the carbonyl group towards nucleophilic attack affords the construction of various organic compounds. Thus, investigations of carbonyl activation applying greener methodologies are highly important. In the present work, among the investigated N-halo compounds, N-fluorobenzenesulfonimide (NFSi) has been found as an efficient and selective catalyst in the reaction of direct esterification of aryl and alkyl carboxylic acids supported by microwave (MW) irradiation. The comprehensive esterification of different benzoic acids and mono-, di- and tri-carboxy alkyl derivatives was performed, whereby significant reaction time reductions were achieved. The presented method used NFSi as an easily manipulatable, non-metal, water- and air-tolerant catalyst, allowing simple synthetic and isolation procedures and energy saving, compared to conventional methodologies. Importantly, in contrast to esterification under thermal conditions, where N-halo compounds behave as pre-catalysts, in the MW-supported protocol, a distinct reaction mechanism has been proposed that assumes NFSi as a sustainable catalyst. Moreover, a scale-up of the industrially important derivative was performed.

Insight into the Mechanism of the Acylation of Alcohols with Acid Anhydrides Catalyzed by Phosphoric Acid Derivatives

Insight into the mechanism of a safe, simple, and inexpensive phosphoric acid (H₃PO₄)-catalyzed acylation of alcohols with acid anhydrides is described. The corresponding in situ-generated diacylated mixed anhydrides, unlike traditionally proposed monoacylated mixed anhydrides, are proposed as the active species. In particular, the diacylated mixed anhydrides act as efficient catalytic acyl transfer reagents rather than as Brønsted acid catalysts simply activating acid anhydrides. Remarkably, highly efficient phosphoric acid (1-3 mol %)-catalyzed acylation of alcohols with acid anhydrides was achieved and a 23 g scale synthesis of an ester was demonstrated. Also, phosphoric acid catalyst was effective for synthetically useful esterification from carboxylic acids, alcohols, and acid anhydride. Moreover, with regard to recent developments in chiral 1,1'-bi-2-naphthol (BINOL)-derived phosphoric acid diester catalysts toward asymmetric kinetic resolution of alcohols by acylation, some phosphate diesters were examined. As a result, a ³¹P NMR study and a kinetics study strongly supported not only the acid-base cooperative mechanism as previously proposed by other researchers but also the mixed anhydride mechanism as presently proposed by us.

Catalytic Reductive Alkylation of Amines in Batch and Microflow Conditions Using a Silicon-Wafer-Based Palladium Nanocatalyst

We describe the development of the catalytic reductive alkylation of amines with aldehydes under the atmospheric pressure of H2 using a brush-like silicon-nanostructure-supported palladium nanoparticle composite (SiNS-Pd) as a silicon-wafer-based reusable heterogeneous catalyst. The present reaction of primary and secondary amines with various aliphatic and aromatic aldehydes in the presence of the catalyst (0.02-0.05 mol % Pd) gave the corresponding secondary and tertiary amines including Lomerizine and Aticaprant in a 68% quantitative yield without overalkylation. We also designed and fabricated a flow device equipped with SiNS-Pd for microflow reactions, which was applied to the gas-liquid-solid triphasic reaction system (i.e., H2 gas, a substrate solution, and a solid catalyst). A multigram-scale reaction of aniline and benzaldehyde was demonstrated to obtain N-benzylaniline (ca. 4 g/day), in which the internal volume of the flow channel was 43 μL, the residence time was approximately 1 s, and the turnover number (TON) reached 4.0 × 104 in a continuous 24 h run (1.7 × 103 h-1; 0.50 s-1).

Cycloaddition of CO2 with epoxides and esterification reactions using the porous redox catalyst Co-POM@MIL-101(Cr)

The catalytic activity of the Co-POM@MIL-101(Cr) composite in solvent-free cycloaddition of CO₂ to epoxides and esterification of acetic acid with alcohols is due to an outer-sphere electron transfer mechanism using the Co(iii)/Co(ii) redox pair.

Long-Lasting Complex Reaction Behavior in a Closed Ferroin-Bromate-Hydroxybenzenesulfonate System

The bromate-phenolsulfonate reaction was found to exhibit spontaneous oscillations in a batch reactor, where the addition of small amounts of ferroin would result in nonoscillatory behavior. As the ferroin concentration was increased, the system produced very rich nonlinear behavior, including three isolated oscillatory regimes that were separated by as long as 48 h nonoscillatory period. The long-lasting nonlinear behavior may be attributed to the slow desulfonation of phenolsulfonate in an acidic solution, forming phenol-like intermediates. However, unlike the bromate-phenol oscillator, oxygen was found to greatly influence the reaction, and various complex oscillations could be observed by tuning the oxygen concentration. Mechanistic studies performed through employing ¹H NMR spectroscopy and mass spectrometry to measure intermediate species at different stages of the reaction were able to identify 1,4-benzoquinone, 2-bromo-1,4-benzoquinone, 2,6-dibromo-1,4-benzoquinone, and 2,4,6-tribromophenol as major components during the reaction.

Esterification of Aryl/Alkyl Acids Catalysed by N-bromosuccinimide under Mild Reaction Conditions

N-halosuccinimides (NXSs) are well-known to be convenient, easily manipulable and low-priced halogenation reagents in organic synthesis. In the present work, N-bromosuccinimide (NBS) has been promoted as the most efficient and selective catalyst among the NXSs in the reaction of direct esterification of aryl and alkyl carboxylic acids. Comprehensive esterification of substituted benzoic acids, mono-, di- and tri-carboxy alkyl derivatives has been performed under neat reaction conditions. The method is metal-free, air- and moisture-tolerant, allowing for a simple synthetic and isolation procedure as well as the large-scale synthesis of aromatic and alkyl esters with yields up to 100%. Protocol for the recycling of the catalyst has been proposed.

Synthesis, Crystal Structure, and Biological Activity of Ethyl 4-Methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylate Polymorphic Forms

Continuing the search for new potential analgesics among the derivatives of 4-methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylic acid, the possibility of obtaining its esters by the alkylation of the corresponding sodium salt with iodoethane in dimethyl sulfoxide (DMSO) at room temperature was studied. It was found that under such conditions, together with the oxygen atom of the carboxyl group, a heteroatom of nitrogen is also alkylated. Therefore, the product of the reaction studied is a mixture of ethyl 4-methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylate (major) and its 1-ethyl-substituted analog (minor). A simple but very effective method of preparative separation of these compounds was proposed. Moreover, the heterogeneous crystallization from ethanol was revealed to result in a monoclinic polymorphic form of ethyl 4-methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylate, while the homogeneous crystallization results in its orthorhombic form. The molecular and crystal structures of both forms were confirmed by X-ray diffraction analysis, and the phase purity by powder diffraction study. The pharmacological tests carried out on the model of a carrageenan edema showed that the screening dose of 20 mg/kg of 1-ethyl-substituted ester and the orthorhombic form of its analog unsubstituted in position 1 exhibited weak anti-inflammatory and moderate analgesic effects. At the same time, the monoclinic form of ethyl 4-methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylate appeared to be both a powerful analgesic and an anti-inflammatory agent that exceeded Piroxicam and Meloxicam in the same doses by these indicators. A detailed comparative analysis of the molecular and crystal structures of two polymorphic forms of ethyl 4-methyl-2,2-dioxo-1H-2λ⁶,1-benzothiazine-3-carboxylate was carried out using quantum chemical calculations of the energies of pairwise interactions between molecules. An explanation of the essential differences of their biological properties based on this was offered.

Efficient synthesis of esters through oxone-catalyzed dehydrogenation of carboxylic acids and alcohols

An environmentally friendly oxone (20 mol%) catalyzed esterification of carboxylic acids with alcohols has been developed, providing an attractive alternative to the construction of valuable carbonyl esters.

Development and Application of a Recyclable High-Load Magnetic Co/C Hybrid ROMP-Derived Benzenesulfonyl Chloride Reagent and Utility of Corresponding Analogues

The development and application of high-load, recyclable magnetic Co/C hybrid ROMP-derived benzenesulfonyl chloride and analogues is reported. The regeneration and utility of these reagents in the methylation/alkylation of various carboxylic acids is demonstrated via efficient retrieval of the magnetic reagent with a neodymium magnet. Additional reactions employing the analogue sulfonic acid and in situ generated magnetic benzenesulfonyl azide are also reported.

Advances in Organic and Organic-Inorganic Hybrid Polymeric Supports for Catalytic Applications

In this review, the most recent advances (2014-2016) on the synthesis of new polymer-supported catalysts are reported, focusing the attention on the synthetic strategies developed for their preparation. The polymer-supported catalysts examined will be organic-based polymers and organic-inorganic hybrids and will include, among others, polystyrenes, poly-ionic liquids, chiral ionic polymers, dendrimers, carbon nanotubes, as well as silica and halloysite-based catalysts. Selected examples will show the synthesis and application in the field of organocatalysis and metal-based catalysis both for non-asymmetric and asymmetric transformations.

In-Water and Neat Batch and Continuous-Flow Direct Esterification and Transesterification by a Porous Polymeric Acid Catalyst

A porous phenolsulphonic acid—formaldehyde resin (PAFR) was developed. The heterogeneous catalyst PAFR was applied to the esterification of carboxylic acids and alcohols, affording the carboxylic acid esters in a yield of up to 95% where water was not removed from the reaction mixture. Surprisingly, the esterification in water as a solvent proceeded to afford the desired esters in high yield. PAFR provided the corresponding esters in higher yield than other homogeneous and heterogeneous catalysts. The transesterification of alcohols and esters was also investigated by using PAFR, giving the corresponding esters. PAFR was applied to the batch-wise and continuous-flow production of biodiesel fuel FAME. The PAFR-packed flow reactor that was developed for the synthesis of carboxylic acids and FAME worked for four days without loss of its catalytic activity.

Novel access to carbonyl and acetylated compounds: the role of the tetra-n-butylammonium bromide/sodium nitrite catalyst

A novel aerobic oxidation of alcohols without the use of any oxidants was developed.

Biomass derived β-cyclodextrin-SO3H as a solid acid catalyst for esterification of carboxylic acids with alcohols

A novel b-cyclodextrin-SO₃H carbon based solid acid catalyst was prepared and proved highly efficient in solvent free esterification of carboxylic acids with alcohols. The catalyst was easily recovered and reused without any impact on the yields.

SO3H and NH2+ functional carbon-based solid acid catalyzed transesterification and biodiesel production

A SO₃H and NH₂⁺ functional carbon-based solid acid was used as a highly active heterogeneous catalyst for the transesterification of various carboxylic methyl esters with alcohols under mild conditions.

On the understanding of BF3·Et2O-promoted intra- and intermolecular amination and oxygenation of unfunctionalized olefins

BF₃·Et₂O was found to be effective for the amination and oxygenation of unfunctionalized olefins. In the presence of 3 equiv. of BF₃·Et₂O, intra- and intermolecular amination and oxygenation reactions could be realized in up to 99% isolated yields.

PMoA/MCM-41 catalyzed aza-Michael reaction: special effects of mesoporous nanoreactor on chemical equilibrium and reaction rate through surface energy transformation

Nanoreactors as catalysts can affect not only speed but also the chemical equilibrium of the reaction under investigation.

New amino butenolides from the bulbs of Fritillaria unibracteata

Five new amino γ-butenolides, fritenolide A (1), B (2), C (3), D (4), and E (5), along with four known compounds, were isolated from the bulbs of Fritillaria unibracteata. Their structures were determined by spectroscopic analysis, including 1D NMR, 2D NMR, HRESIMS, HRESIMS/MS, IR, and CD techniques. All isolates were evaluated for the protective activity on injured hepatocytes and cytotoxic activity on human cancer cells in vitro. The unusual amino butenolides were isolated from the Liliaceae family for the first time.