Highly efficient heterogeneous acylations of aromatic compounds with acid anhydrides and carboxylic acids by montmorillonite-enwrapped titanium as a solid acid catalyst

Montmorillonite-enwrapped titanium hydroxide species (Ti⁴⁺-mont) acted as a highly efficient heterogeneous acid catalyst for the acylation of aromatic compounds with acid anhydrides or carboxylic acids. The catalytic activity of the Ti⁴⁺-mont was higher than those of other acid catalysts such as zeolites, SO ₄ ^2? /ZrO₂ and p-toluenesulfonic acid. For example, the reaction of anisole with dodecanoic acid in the presence of the Ti⁴⁺-mont catalyst gave 1-(4-methoxyphenyl)-1-dodecanone in 97% yield. Furthermore, the Ti⁴⁺-mont catalyst was easily separated from the reaction mixture and was recyclable.     

Highly efficient esterification of carboxylic acids with alcohols by montmorillonite-enwrapped titanium as a heterogeneous acid catalyst

Montmorillonite-enwrapped titanium catalyst was found to efficiently promote the esterification of carboxylic acids with alcohols. In comparison to other catalysts reported to date, this heterogeneous catalyst offers a remarkably simple workup procedure, and is reusable without any appreciable loss in its activity and selectivity.     

Fe-exchanged montmorillonite K10--the first heterogeneous catalyst for acylation of sulfonamides with carboxylic acid anhydrides

Fe-exchanged montmorillonite K10 catalyzes a highly efficient reaction between sterically and electronically diverse sulfonamides and carboxylic acid anhydrides to furnish N-acylsulfonamides in excellent yield and high selectivity. The catalyst can also be reused several times.     

Tf2O as a rapid and efficient promoter for the dehydrative Friedel-Crafts acylation of aromatic compounds with carboxylic acids

The Friedel-Crafts acylation of aromatic compounds with carboxylic acids was investigated in the presence of Tf₂O. The reaction was carried out efficiently and very rapidly under mild reaction conditions without the need of any catalyst.     

Copper-catalyzed synthesis of aromatic carboxylic acids from arylboronic acids and acetyl acetate

A simple and efficient copper-catalyzed method for the synthesis of aromatic carboxylic acids in moderate to high yields with great functional-group compatibility in the substrates has been developed. The new method uses readily available arylboronic acids and acetyl acetate as the starting materials and inexpensive CuI as the catalyst.     

The optimized separation of aromatic carboxylic acids by HPLC

The optimization of the separation of eight aromatic carboxylic acids, using Hypersil SAS and MOS reverse phase columns, with respect to eluent (methanol : water) composition, pH, and temperature, is described. Window diagram techniques are used and the pH of the aqueous buffer and elution temperature are shown to be more critical than eluent composition.     

Adsorption and self-assembly of aromatic carboxylic acids on Au/electrolyte interfaces

The adsorption and self-assembly of benzoic acid (BA), isophthalic acid (IA), and trimesic acid (TMA) on Au(111) single crystals and on Au(111-25 nm) quasi-single crystalline film electrodes have been investigated in 0.1 M HClO₄ by combining in situ surface-enhanced infrared reflection absorption spectroscopy (SEIRAS) and scanning tunneling microscopy (STM) with cyclic voltammetry. All three acids are physisorbed on the electrode surface in a planar orientation at negative charge densities. Excursion to positive charge densities (or more positive potentials) causes an orientation change from planar to perpendicular. Chemisorbed structures are formed through the coordination of a deprotonated carboxyl group to the positively charged electrode surface. The three acid molecules assemble in different ordered patterns, which are controlled by π-stacking (BA) or intermolecular hydrogen bonds between COOH groups (IA, TMA). A detailed analysis of the potential and time dependencies of the ν_(C=O), ν_s(OCO), and ν_(C–OH) vibration modes shows that the strength of lateral interactions increases upon chemisorption with an increasing number of COOH groups in the sequence of BA<IA<TMA. The vibration bands shift to higher wavenumbers due to dipole–dipole coupling, Stark tuning, and electron back donation from the electrode to COO⁻. In addition, an “indirect” electron donation to the COOH groups takes place via the conjugated molecular skeleton superimposed on the intermolecular hydrogen bonding. Figure In-situ STM images of the physisorbed and chemisorbed adlayers of isophthalic acid on Au(111)-(1 × 1), the corresponding cyclic voltammogram and principle of the ATR-SEIRAS set-up     

Conversion of municipal solid waste into carboxylic acids by anaerobic countercurrent fermentation

Municipal solid waste (MSW) and sewage sludge (SS) were combined and anaerobically converted into carboxylate salts by using a mixed culture of acid-forming microorganisms. MSW is an energy source and SS is a source of nutrients. In this study, MSW and SS were combined, so they complemented each other. Four fermentors were arranged in series for a countercurrent fermentation process. In this process, the solids and liquid were transferred in opposite directions, with the addition of fresh biomass to fermentor 1 and fresh liquid media to fermentor 4. An intermediate lime treatment of solids exiting fermentor 3 before entering fermentor 4 was applied to improve the product acid concentration from the untreated MSW/SS fermentations. All fermentations were performed under anaerobic conditions at 40°C. Calcium carbonate was added to neutralize the carboxylic acids and to control the pH. Iodoform was used as a methanogen inhibitor. Carboxylic acid concentration and gas composition were determined by gas chromatography. Substrate conversion was measured by volatile solids loss, and carboxylic acid productivity was calculated as the function of the total carboxylic acids produced, the amount of liquid in all fermentors, and time. The addition of intermediate lime treatment increased product concentration and conversion by approx 30 and 15%, respectively. The highest carboxylic acid concentrations for untreated MSW/SS fermentations with and without intermediate lime treatment were 22.2 and 17.7 g of carboxylic acid/L of liquid, respectively. These results confirm that adding a treatment step between fermentor 3 and fermentor 4 will increase the digestibility and acid productivity of the fermentation.     

Photophysical properties of praseodymium complexes with aromatic carboxylic acids: double light conversion both in ultraviolet and visible region

A series of luminescent praseodymium complexes with different aromatic carboxylic acids have been synthesized and characterized. The photophysical properties of these complexes have been studied with ultraviolet spectra, phosphorescence spectra and fluorescence spectra. Ultraviolet absorption spectra show that the praseodymium complexes systems with aromatic carboxylate form the more extensive conjugated systems to be suitable for the distribution of electron in the whole coordination environment, resulting in the energy decrease and red-shifts of ultraviolet spectral bands. Phosphorescence spectra suggest that excited triplet state of aromatic carboxylic acids, which can indicate the energy match and intermolecular energy transfer process between the excited triplet state of ligands and the resonant emissive energy level of Pr ions. The emission spectra of all praseodymium complexes show two emission peaks under the excitation band of 245 nm at about 395 and 595 nm, respectively, while one peak at about 595 nm under 415 nm excitation, which attributed to be 1S0-->1I6 (395 nm) transition and the characteristic emission 1D2-->3H4 (595 nm) transition of Pr3+ ion. The 1S0-->1I6 transition can be speculated to belong to the transition of charge transfer state, and the 1D2-->3H4 can be further proved that there exists an antenna effect in the luminescence of praseodymium with aromatic carboxylic acids. In conclusion, the praseodymium complexes systems can realize the double proton light conversion both in the ultraviolet and visible region, which can be further studied to have potential application.     

3,4,5-Trifluorobenzeneboronic acid: a mild and versatile catalyst for the one-pot synthesis of acyl azides from carboxylic acids

Acyloxyboron intermediates generated from carboxylic acids and 3,4,5-trifluorobenzeneboronic acid react with sodium azide to furnish the corresponding acyl azides in moderate to good yields.     

Repurposing n-butyl stannoic acid as highly efficient catalyst for direct amidation of carboxylic acids with amines

This is the first-time report on the repurposing n-butyl stannoic acid as a catalyst for direct amidation of carboxylic acids with amines. Notably, efficient amidation observed in comparison with all other catalytic methods reported up until now. The protocol has successfully applied to the synthesis of a variety of amides. Moderate reaction parameters, clean amidation with excellent yields of desired amides, ability to tolerate a variety of functional groups, easy product isolation; commercial availability and recyclability of the catalyst are key advantages of the current protocol.     

Rapid and mild sulfonylation of aromatic compounds with sulfonic acids via mixed anhydrides using Tf2O

An efficient and direct sulfonylation of aromatic compounds with sulfonic acids is described via mixed anhydrides in short reaction times using Tf₂O in nitromethane at room temperature.     

Silica sulfuric acid as a highly efficient catalyst for the synthesis of diarylacetic acids

An efficient heterogeneous method for the synthesis of diarylacetic acids was developed utilizing silica sulfuric acid as a catalyst. The reaction is highly efficient with a small amount of catalyst for the combination of a variety of electron-neutral to electron-rich arenes with glyoxylic acid. The reaction can also be utilized to synthesize unsymmetric derivatives from activated mandelic acids in good to excellent yields.     

Highly efficient ring opening reactions of epoxides with deactivated aromatic amines catalyzed by heteropoly acids in water

Heteropoly acid was found to be an effective and efficient catalyst for the ring opening reaction of epoxides with various aromatic amines to produce the corresponding β-amino alcohols in moderate to excellent yields in water. This method provides a new and efficient protocol in terms of mild reaction conditions, clean reaction profiles, small quantity of catalyst, and simple work-up procedure.     

Advances in self-assembly and regulation of aromatic carboxylic acid derivatives at HOPG interface

Aromatic carboxylic acid self-assembly has been a hot research field for many scientists due to its strong coordination ability and flexible coordination mode.The hydrogen bond formed between aromatic carboxylic acids is a strong intermolecular force and has directionality and saturation,which plays a very important role in the self-assembly and regulation of aromatic carboxylic acids.In this review,we introduce surface organization formed by aromatic carboxylic acids with the aid of scanning tunneling microscopy(STM).These two-dimensional structures include molecular templates,host-guest systems,and photo-isomerization structures.We also emphasize the thermodynamics and dynamics,which are important research topics of current and future study.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids II. Separation of aliphatic carboxylic acids with pyromellitic acid as eluent and with suppressed conductimetric detection

The application of zirconium-modified silica gels (Zr-Silica) as stationary phases for ion-exclusion chromatography with conductimetric detection (IEC–CD) for C₁–C₈ aliphatic carboxylic acids (formic, acetic, propionic, butyric, valeric, caproic, heptanoic and caprylic acids) was carried out using pyromellitic acid as the eluent. Zr-Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. An ASRS-Ultra anion self-regenerating suppressor in the K⁺ form was used for the enhancement of conductimetric detector response of these aliphatic carboxylic acids. A Zr-Silica adsorbed on 10 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in IEC–CD for the separation of these aliphatic carboxylic acids. Excellently simultaneous separation and highly sensitive detection for these aliphatic carboxylic acids were achieved in 25 min by IEC–CD with the Zr-Silica column (250×4.6 mm I.D.) and a 0.2 mM pyromellitic acid containing 0.15% heptanol as the eluent.     

Use of beta-cyclodextrin bonded phase with s-triazine moiety in the spacer for separation of aromatic carboxylic acid isomers by high-performance liquid chromatography

The separation and retention behavior of five aromatic carboxylic acid isomers was investigated by means of high-performance liquid chromatography (HPLC) using a β-cyclodextrin bonded phase with s-triazine ring in the spacer. The influence of mobile phase pH on the retention was examined. The presence of s-triazine moiety in the spacer enhances greatly the selectivity of the isomers of aromatic carboxylic acids. Baseline separations of the five aromatic carboxylic acid isomers were achieved. In particular, the isomers of toluic, aminobenzoic, nitrobenzoic and hydroxybenzoic acid were successfully and effectively separated. The chromatographic results indicate that, in addition to inclusion complexation, π-π interaction and hydrogen bonding interaction between the bonded phase and analytes play significant roles in the retention of these acid isomers. Different elution orders were observed for these acidic solutes with different substituents. Possible retention mechanisms are discussed.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids I. Separation of benzenecarboxylic acids with tartaric acid as eluent and with UV-photometric detection

The application of zirconium-modified silica gels (Zr–Silicas) as stationary phases for ion-exclusion chromatography with UV-photometric detection (IEC–PD) for mono-, di-, tri- and tetrabenzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, salicylic and benzoic acids) and phenol was carried out using tartaric acid as the eluent. Zr–Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. The effect of the amount of zirconium adsorbed on silica gel on chromatographic behavior of these benzenecarboxylic acids and phenol was investigated. As a result, Zr–Silica adsorbed on 20 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in the IEC–PD for the simultaneous separation of these benzenecarboxylic acids and phenol. Excellent simultaneous separation and highly sensitive UV detection at 254 nm for these benzenecarboxylic acids and phenol were achieved in 20 min by the IEC–PD using the Zr–Silica column (250×4.6 mm I.D.) and a 10 mM tartaric acid at pH 2.5 as eluent.     

Polymeric ionic liquid as additive for the high speed and efficient separation of aromatic acids by co-electroosmotic capillary electrophoresis

A simple and reliable co-electroosmotic capillary electrophoresis system for the fast determination of aromatic acids has been developed by employing poly (1-vinyl-3-butylimidazolium bromide) as the background electrolyte modifier. The polymeric ionic liquid was synthesized by the conventional radical polymerization. The reversed electroosmotic flow was obtained by adding a small amount of the polymeric ionic liquid (0.0006%, w/v) to the electrolyte. To further improve the resolution of aromatic acids, conditions including the concentration of polymeric ionic liquid and pH of background electrolytes were optimized. All eight aromatic acids were baseline resolved in one measurement in a short time (less than 3.5 min) under optimized conditions, 100 mM NaH₂PO₄ buffer containing 0.006% (w/v) polymeric ionic liquid, pH 6.0. Separation efficiencies were in the range from 355,000 to 943,000 (plates/m). Satisfactory reproducibility on the basis of the migration time of analytes was achieved. RSDs (n = 3) were less than 0.33% except the p-aminobenzoic acid (0.9%). The applicability of the present method has been demonstrated for the determination of water-soluble aromatic acids in a common drug for external use.