Showing papers on "Benzoic acid published in 2016"

Pd(II)-catalysed meta -C–H functionalizations of benzoic acid derivatives

Abstract: Benzoic acids are highly important structural motifs in drug molecules and natural products. Selective C-H bond functionalization of benzoic acids will provide synthetically useful tools for step-economical organic synthesis. Although direct ortho-C-H functionalizations of benzoic acids or their derivatives have been intensely studied, the ability to activate meta-C-H bond of benzoic acids or their derivatives in a general manner via transition-metal catalysis has been largely unsuccessful. Although chelation-assisted meta-C-H functionalization of electron-rich arenes was reported, chelation-assisted meta-C-H activation of electron-poor arenes such as benzoic acid derivatives remains a formidable challenge. Herein, we report a general protocol for meta-C-H olefination of benzoic acid derivatives using a nitrile-based sulfonamide template. A broad range of benzoic acid derivatives are meta-selectively olefinated using molecular oxygen as the terminal oxidant. The meta-C-H acetoxylation, product of which is further transformed at the meta-position, is also reported.

A General Method for Aminoquinoline-Directed, Copper-Catalyzed sp2 C–H Bond Amination

Abstract: An operationally simple and general method for copper-catalyzed, aminoquinoline-assisted amination of β-C(sp2)-H bonds of benzoic acid derivatives is reported. The reaction employs Cu(OAc)2 or (CuOH)2CO3 catalysts, an amine coupling partner, and oxygen from air as a terminal oxidant. Exceptionally high generality with respect to amine coupling partners is observed. Specifically, primary and secondary aliphatic and aromatic amines, heterocycles, such as indoles, pyrazole, and carbazole, sulfonamides, as well as electron-deficient aromatic and heteroaromatic amines are competent coupling components.

Ru-Catalyzed C–H Arylation of Fluoroarenes with Aryl Halides

Abstract: Although the ruthenium-catalyzed C–H arylation of arenes bearing directing groups with haloarenes is well-known, this process has never been achieved in the absence of directing groups. We report the first example of such a process and show that unexpectedly the reaction only takes place in the presence of catalytic amounts of a benzoic acid. Furthermore, contrary to other transition metals, the arylation site selectivity is governed by both electronic and steric factors. Stoichiometric and NMR mechanistic studies support a catalytic cycle that involves a well-defined η6-arene-ligand-free Ru(II) catalyst. Indeed, upon initial pivalate-assisted C–H activation, the aryl-Ru(II) intermediate generated is able to react with an aryl bromide coupling partner only in the presence of a benzoate additive. In contrast, directing-group-containing substrates (such as 2-phenylpyridine) do not require a benzoate additive. Deuterium labeling and kinetic isotope effect experiments indicate that C–H activation is both reve...

Charge-Transfer-Induced Fluorescence Quenching of Anthracene Derivatives and Selective Detection of Picric Acid.

Abstract: 2,6-Divinylpyridine-appended anthracene derivatives flanked by two alkyl chains at the 9,10-position of the core have been designed, synthesized, and characterized by NMR, MALDI-TOF, FTIR, and single-crystal XRD. These anthracene derivatives are able to recognize picric acid (2,4,6-trinitrophenol, PA) selectively down to parts per billion (ppb) level in aqueous as well as nonaqueous medium. Fluorescence emission of these derivatives in solution is significantly quenched by adding trace amounts of PA, even in the presence of other competing analogues, such as 2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (NP), nitrobenzene (NB), benzoic acid (BA), and phenol (PH). The high sensitivity of these derivatives toward PA is considered as a combined effect of the proton-induced intramolecular charge transfer (ICT) as well as electron transfer from the electron-rich anthracene to the electron-deficient PA. Moreover, visual detection of PA has been successfully demonstrated in the solid state by using different substrates.

Thermokinetic stability of phycocyanin and phycoerythrin in food-grade preservatives

Abstract: Phycocyanin (PC) and phycoerythrin (PE) are the main phycobiliproteins (PBPs) with application as colorants in food industries. In the present study, the thermokinetic stability of PBPs extracted and purified from a hot spring cyanobacterium, Nostoc sp. strain HKAR-2, was investigated. The individual components of PC and PE were isolated with a high purity ratio of 3.18 (A615/A280) and 7.2 (A563/A280), respectively. The thermokinetic stability of purified PC and PE was studied in the presence of edible preservatives such as benzoic acid, citric acid, sucrose, ascorbic acid, and calcium chloride over 30 days of incubation at 4, 25, and 40 °C. The rate of degradation (k value) of PC/PE was increased in the control (without preservative), while it declined in the presence of preservatives. The k value (day−1) was found to be the lowest for benzoic acid-treated PC/PE in comparison to the control at 4 °C. The rate of degradation also declined in benzoic acid-treated PC (0.008 day−1) and PE (0.012 day−1) at 40 °C in comparison with the control. Citric acid and sucrose were also found to maintain the stability of both PC and PE at the same temperature. Calcium chloride and ascorbic acid were shown to be the preservatives that support the least stability of PC and PE in comparison to the other preservatives studied. Overall, benzoic acid was found to be the best preservative for both PC and PE at 4 °C.

Functional Group Adsorption on Calcite: I. Oxygen Containing and Nonpolar Organic Molecules

Abstract: Considerable interest in calcite crystallization has prompted many studies on organic molecule adsorption. However, each study has explored only a few compounds, using different methods and conditions, so it is difficult to combine the results into a general model that describes the fundamental mechanisms. Our goal was to develop a comprehensive adsorption model from the behavior of a range of organic compounds by exploring how common functional groups interact with calcite and the effects of various side groups and hydrogen on adsorption. We used density functional theory, with semiempirical dispersion corrections (DFT-D2), to determine adsorption energy on calcite {10.4} for nonpolar (benzene, ethane, and carbon dioxide) and oxygen containing polar molecules (water, methanol, ethanol, phenol, formic acid, acetic acid, propanoic acid, benzoic acid, formaldehyde, acetaldehyde, propionaldehyde, benzaldehyde, dimethyl ether, acetone, and furan). From the adsorption energies, within the transition state theo...

Generation of hydrogen peroxide and hydroxyl radical resulting from oxygen-dependent oxidation of l-ascorbic acid via copper redox-catalyzed reactions

Abstract: The generation of hydrogen peroxide (H2O2) and hydroxyl radical (HO˙) during the oxidation of L-ascorbic acid (L-AA) by oxygen with copper as a catalyst was investigated to set up the O2/Cu/L-AA process with benzoic acid (BA) as a probe reagent. The high concentration of H2O2 that is generated undergoes an intramolecular two-electron transfer and is further activated by the intermediate cuprous copper [Cu(I)] to yield HO˙ as a product, resulting in significant degradation of BA. Dehydroascorbic acid, 2,3-diketogulonic acid, and L-xylosone were the predominant detected products of the oxidation of L-AA. However, the generation of H2O2 and degradation of BA were regulated by variations in pH, which results from the contradiction between protonated L-AA that is difficult to chelate with Cu(II) via electron transfer and hydrogen ions (H+), which are indispensable for the generation of H2O2. Furthermore, the concentration of H2O2 and degradation of BA increased with an increase in the dosage of L-AA. Trace amounts of Cu(II) are effective for catalyzing the oxidation of L-AA, whereas the generation of H2O2 and degradation of BA increased with an increase in the dosage of Cu(II). Owing to the formation of Cu(I) chloride complexes or Cu(II) chloride complexes, the addition of chloride (Cl−) could inhibit the generation of H2O2 and degradation of BA.

Selective hydrogenation of aromatic carboxylic acids over basic N-doped mesoporous carbon supported palladium catalysts

Abstract: Mesoporous carbon nitride (MCN) has been prepared through a simple polymerization reaction between ethylenediamine (EDA) and carbon tetrachloride (CTC) by a nano hard-templating approach. The obtained MCN possesses high surface area (166.3 m 2 /g), average pore size of 9.2 nm and high N content (up to 18.5 wt%). The negative charge and the basicity on MCN surface are originated from its rich carbon nitride heterocycles, which notably improves the surface hydrophilicity and the adsorption of acidic molecules. Furthermore, MCN can be adopted as the proper support for highly dispersed Pd NPs with well-controlled size distribution. Compared with microporous N-doped active carbon with low N-content, the MCN-supported Pd catalyst shows an enhanced activity in water phase for the selective ring hydrogenation of benzoic acid, benzamide and phenol, in which 11.3 times higher activity in comparison to undoped catalyst is achieved. Wide characterizations reveal that big pore size, selective adsorption for acid substrate and strong interaction between N and Pd may lead to the high activity of Pd/MCN.

Oxidation of benzyl alcohol catalyzed by gold nanoparticles under alkaline conditions: weak vs. strong bases

Abstract: Gold nanoparticles have shown excellent catalytic properties in selective oxidation of alcohols in the presence of base; however, the influence of the nature and concentration of the base on gold catalyst activity and selectivity is not completely understood. We here present a study of the effect of using weak and strong bases on the conversion and selectivity of PVA-stabilized gold nanoparticles supported on titania (AuPVA/TiO2) for benzyl alcohol oxidation. The increase in the concentration of base had little effect on conversion when a weak base was used (K2CO3, Na2B4O7 and Na(CH3COO)), due to the buffer effect, but strongly affected selectivity. The bases with higher pKa values provided higher conversions and increased production of benzoic acid. For the strong base NaOH, benzoic acid was always the major product, although conversion decreases in excess of base. The formation of benzoic acid is avoided by using K2CO3 in non-aqueous media; benzaldehyde is the main product in cyclohexane whereas benzyl benzoate is also formed in significant amounts in solvent-free conditions. The promotion effect observed in the presence of base was discussed in terms of reaction mechanism.

Selectivity Control in Palladium-Catalyzed Alcohol Oxidation through Selective Blocking of Active Sites

Abstract: Stabilized metal nanoparticles (NPs) have received wide interest in a number of liquid-phase catalytic transformations, but the role of the capping/protective agent is still debated. Operando attenuated total reflection infrared (ATR-IR) spectroscopy enabled us to obtain unprecedented molecular level insights into the selectivity issue induced by the presence of the protective agent by following the liquid-phase benzyl alcohol oxidation on Pd/Al2O3. Supported Pd NPs protected by poly(vinyl alcohol) (PVA) showed a lower rate of benzaldehyde decarbonylation compared to unprotected Pd nanoparticles and, as a result, an improved selectivity toward the aldehyde. In addition, also the further oxidation of benzaldehyde to benzoic acid was reduced by the presence of PVA. In combination with considerations on adsorption site occupancy from CO adsorption, we ascribed this behavior to a selective blocking operated by PVA especially of Pd(111) facets, which are active in the decarbonylation process of benzaldehyde du...

Application of nanoparticle-immobilized thermostable β-glucosidase for improving the sugarcane juice properties

Abstract: β-glucosidases are among the key enzymes for juice and beverage industries. They are responsible for the release of aromatic compounds in fruits and fermentation products. In this study, β-glucosidase was isolated, purified, and characterized from an indigenously developed Bacillus subtilis mutant PS-5CM-UM3. It is a 56 kDa protein monomer (isoelectric point of 5.6) belonging to 1 glycosyl hydrolase family. The purified β-glucosidase was immobilized on SiO 2 nanoparticles (with 52% efficiency and 14.1% yield) to improve the thermostability and Michaelis constant (K m ) value of β-glucosidase from 0.9 to 1.1 mM. The immobilized enzyme showed improved storage stability and was reusable for up to 10 cycles with 70% residual activity. β-glucosidase treatment in sugarcane juice elevated the phenolics content with about 2.6 folds and 2.4 folds increase in p-hydroxy benzoic acid (PHBA) and gallic acid, respectively. The results show that recyclable immobilized enzyme system is a novel green approach for improving the sugarcane juice properties. Industrial relevance In this study, β-glucosidase originally isolated and purified from an indigenously developed Bacillus subtilis mutant was immobilized on SiO 2 nanoparticles. The immobilization has improved the thermostability, storage stability, and Michaelis constant (K m ) value of the β-glucosidase. The immobilized β-glucosidase is now reusable for 10 cycles with 70% residual activity. Further, β-glucosidase treatment in sugarcane juice elevated the phenolics content with about 2.6 folds and 2.4 folds increase in p-hydroxy benzoic acid (PHBA) and gallic acid, respectively. Hence, this study provides a green and sustainable approach for the food industry to efficiently enhance the juice properties.

Solar thermoelectric field plus photocatalysis for efficient organic synthesis exemplified by toluene to benzoic acid

Abstract: The solar thermal electrochemical process synthesis of benzoic acid is an efficient way for organic synthesis based upon solar energy utilization. Graphite and platinum anodes have been developed with high yield and selectivity of benzoic acid. In this article, we present the first demonstration of the solar thermal-electro-photo field for efficient benzoic acid synthesis by using TiO2 nanotubes electrode. By adjusting the three-solar field process, toluene is oxidized at the surface of the photoactive, electrically driven, heat activated TiO2 nanotubes electrode. Results showed that, the synergistic effect of the three fields was found for enhancement of toluene oxidation at TiO2 electrode. The yield of benzoic acid and conversion of toluene is greatly improved with temperature, and arriving to 26.1% and 62.6% at 90 °C, respectively. In this process, solar thermal decreases the electrolysis potential of toluene oxidation. Hydroxyl, carboxyl and OOH groups, as well as the emergence of TiOC bond at the surface of the TiO2 nanotubes electrode, lead to an increased UV and visible absorption and a significant enhancement of TiO2 photocatalytic properties to increase the yield of benzoic acid. Simultaneously, an applied solar electric potential promotes the separation of photogenerated electrons and holes. As a result the efficiency of TiO2 photocatalysis enhanced.

Microkinetic Modeling of Benzyl Alcohol Oxidation on Carbon‐Supported Palladium Nanoparticles

Abstract: Six products are formed from benzyl alcohol oxidation over Pd nanoparticles using O2 as the oxidant: benzaldehyde, toluene, benzyl ether, benzene, benzoic acid, and benzyl benzoate. Three experimental parameters were varied here: alcohol concentration, oxygen concentration, and temperature. Microkinetic modeling using a mechanism published recently with surface intermediates was able to produce all 18 trends observed experimentally with mostly quantitative agreement. Approximate analytical equations derived from the microkinetic model for isothermal conditions reproduced the isothermal trends and provided insight. The most important activation energies are Ea2=57.9 kJ mol₋1, Ea5=129 kJ mol₋1, and Ea6=175 kJ mol₋1, which correspond to alcohol dissociation, alkyl hydrogenation, and the reaction of alkyl species with alkoxy species. Upper limits for other activation energies were identified. The concepts of a sticking coefficient and steric factor in solution were applied.

Degradation of organic contaminants by activated persulfate using zero valent copper in acidic aqueous conditions

Abstract: Recently, persulfate (PS) has fascinated practitioners of water treatment as a promising oxidant for in situ chemical oxidation. In this study, zero valent copper (nZVC) particles were employed as an activator for PS to degrade organic contaminants. Benzoic acid (BA) was almost completely degraded in 25 min, and the nZVC/PS process exhibited a ubiquitous oxidizing capacity on various organic contaminants (including acid orange 7, nitrobenzene, dimethyl phthalate, diethylstilbestrol, bisphenol A, and 2,4-dichlorophenol). The mechanism investigation showed that PS can accelerate the corrosion of nZVC to release Cu+ in acidic aqueous conditions, and the reactive radicals were generated through the further activation of PS by intermediate Cu+ via a Fenton-like reaction. Both sulfate radical (SO4−˙) and hydroxyl radical (˙OH) were considered as the primary reactive radicals in the nZVC/PS process due to the intense inhibition with the addition of methanol (MA) and tert-butyl alcohol (TBA). Moreover, the degradation rate of BA increased gradually with an increase of nZVC dosage, and the decrease of the initial pH range from 5.4 to 2.0.

Enzymatic Acylation of Anthocyanin Isolated from Black Rice with Methyl Aromatic Acid Ester as Donor: Stability of the Acylated Derivatives

Abstract: The enzymatic acylation of anthocyanin from black rice with aromatic acid methyl esters as acyl donors and Candida antarctica lipase B was carried out under reduced pressure. The highest conversion of 91% was obtained with benzoic acid methyl ester as acyl donor; cyanidin 3-(6″-benzoyl)-glucoside, cyanidin 3-(6″-salicyloyl)-glucoside, and cyanidin 3-(6″-cinnamoyl)-glucoside were successfully synthesized. This is the first report on the enzymatic acylation of anthocyanin from black rice with methyl aromatic esters as acyl donors and lipase as biocatalyst. Furthermore, the acylation with aromatic carboxylic acids enhanced both the thermostability and light resistivity of anthocyanin. In particular, cyanidin 3-(6″-cinnamoyl)-glucoside was the most stable among the three acylated anthocyanins synthesized.

2,3-Butanediol dehydration catalyzed by silica-supported sodium phosphates

Abstract: Catalytic gas phase dehydration of 2,3 butanediol (BDO) was studied in the fixed bed reactor over silica-supported sodium phosphates for a wide range of Na/P ratios (Na/P = 0–3) and variable content of phosphates. Major products were 1,3-butadiene (BD) and methyl ethyl ketone (MEK) for long contact times. 3-Buten-2-ol (3B2OL) and MEK are major products for the short contact times. Achieved yields of elimination products (BD + 3B2OL) were over 60% per pass at Na/P = 1.8–1.9 which is the optimum combination of acidic and basic components for the long term production of BD or 3B2OL from BDO. Minor products detected at short contact times (2,3-epoxybutane, 2,3-butanedione and acetoin) imply that hydrogen transfer and dehydrative epoxidation are minor pathways. Mass transport limitations are more apparent for BDO → 3B2OL → BD route (elimination) than for BDO → MEK route (rearrangement). This leads to the lower selectivity of elimination products at long contact time and/or insufficient flow rate of the carrier gas. 2-butanol dehydration using the same catalysts shows considerable selectivity to 1-butene (1-BT) providing evidence for E 1cB elimination mechanism that requires concerted action of acid-base pairs. NH 3 and CO 2 TPD studies confirmed existence of weak acid and basic sites for the sodium phosphates supported on silica. High affinity adsorption of pyridine (Py) and benzoic acid (BA) shows maximum of acid/base ratio at Na/P∼1.5–2. According to XRD and 31 P MAS NMR data the catalysts providing the best performance are composed of pyrophosphates and tripolyphosphates finely dispersed on the surface of silica. XPS shows considerable migration of surface sodium cations into the bulk when Na/P ratio exceeds 1.4.

Electrochemical oxidation of RB-19 dye using a highly BDD/Ti: Proposed pathway and toxicity

Abstract: In this work, the electrolysis of Reactive Blue 19 (RB-19, a toxic textile dye with a high half-life) using a highly non-commercial boron-doped diamond film on titanium substrate (BDD/Ti) was studied. The BDD film with a B/C ratio of 15,000 ppm, a doping level around 10 19 cm −3 and higher content of sp 3 (diamond) than sp 2 (graphite) was produced with high quality and stability. Under appropriate conditions, the electrode promoted complete decolorization of RB-19, together with 99% of TOC removal and a significant decrease in toxicity against V. fischeri . Furthermore, benzene rings, aromatic amines and naphthalene could be removed also during the electrodegradation. The decay in dye concentration followed pseudo-first order kinetics and the values of the apparent rate constant increased with increasing current density applied. In addition, the main intermediates compounds of RB-19 degradation on BDD/Ti based on HPLC–MS analysis were amino-anthraquinone, tautomers keto-enolic, hydroquinone and benzoquinone, benzoic acid, phenol and acid aliphatic, such as oxalic acid. It is concluded that electrochemical oxidation using a BDD/Ti anode represents a satisfactorily method for the removal of RB-19 in aqueous solutions.

Novel aluminium exchanged dodecatungstophosphoric acid supported on K-10 clay as catalyst: benzoylation of diphenyloxide with benzoic anhydride

Abstract: A series of (20% w/w) aluminium exchanged dodeca-tungstophosphoric acids (DTP) (Alx-DTP, x = 0.33–1) supported on montmorillonite K-10 clay were synthesized and completely characterized by sophisticated techniques. These catalysts were used for the selective benzoylation of diphenyl oxide with benzoic anhydride to a mono acylated product. Al0.66-DTP/K-10 catalyst showed the best activity amongst other aluminium substituted catalysts and Cs2.5H0.5PW12O40 (Cs-DTP)/K-10. Different supports such as ZrO2, SnO2 and K-10 were used to study the effect of support on the acidic property and activity of Al0.66-DTP supported catalysts in the benzoylation reaction. The order of activity was Al0.66-DTP/K-10 > Al0.66-DTP/SnO2 > Al0.66-DTP/ZrO2. The effect of benzoylating agents such as benzoic anhydride, benzoyl chloride and benzoic acid on the conversion and rate was also studied. Benzoic anhydride showed the highest reactivity. Eley–Rideal mechanism was found to be consistent with the data. The activation energy for benzoylation of DPO was calculated as 22 kcal mol−1, which further supports that the reaction is kinetically controlled. Al0.66-DTP/K-10 was an active and robust catalyst.