Oxidation Of Carboxylic Acids Research Articles

G‐C3N4 Photocatalyzed Decarboxylative Oxidation of Carboxylic Acids and the Oxidation of Alkenes and Alkanes

AbstractThe decarboxylative oxygenation of readily available carboxylic acids as well as the oxidation of alkenes and alkanes has been accomplished through visible light using g‐C3N4 as a robust and recyclable catalyst. The scalable protocol furnishes an array of aldehydes and ketones under mild reaction conditions, requiring only molecular oxygen as an oxidant. Notably, no addition of stochiometric amounts of base is required, and furthermore, the reaction proceeds efficiently open to the air.

Decarboxylative Oxidation of Carboxylic Acids Using Photocatalysis and Copper Catalysis

AbstractA decarboxylative oxidation of carboxylic acids was developed through visible-light-induced photocatalysis with molecular oxygen as a green oxidant and copper as a co-catalyst. This reaction worked smoothly on various type of acids, and could potentially be used in modifications of natural products. The high efficiency of this transformation was demonstrated on over 40 substrates.

Anodically‐Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes

AbstractElectrochemically driven C−C coupling has the potential to reduce the cost and environmental impact of some organic syntheses currently accomplished through thermochemical methods. Here, we use electrochemical oxidation of carboxylic acids as a source of reactive carbon‐centered radicals that enable radical addition to alkenes in the anode boundary layer. We demonstrate an optimization of reaction conditions to suppress the thermodynamically favored, but synthetically undesirable radical self‐coupling in favor of radical addition to styrene. In methanol solvent, 88 % selectivity and 72 % Faradaic efficiency for targeted functionalized benzenes are achieved. For low current densities, iridium anodes outperform platinum, gold, palladium, and glassy carbon anodes. With constant potential or constant current electrolyses, the deposition of organic by‐products on the catalyst surface leads to anode passivation. We show that periodic cathodic current pulses effectively regenerate the catalyst. Lastly, we confirm the role of free radicals in the reaction mechanism with a radical trap.

Secondary organic aerosol formation in China from urban-lifestyle sources: Vehicle exhaust and cooking emission.

An increasing number of people tend to live in cities, where they suffer from serious air pollution from anthropogenic sources. Vehicle exhaust and cooking emission are closely related to daily life of urban residents, and could be defined as "urban-lifestyle sources". The primary emissions of urban-lifestyle sources tend to form abundant secondary organic aerosols (SOA) through complicated atmospheric chemistry processes. The newly formed SOA is a kind of complex mixture and causes considerable health effects with high uncertainty. Most studies focus on formation pathway, mass growth potential and chemical feature of urban-lifestyle SOA under simple laboratory conditions. Few studies have measured the urban-lifestyle SOA in ambient air, let alone verified laboratory findings under complicated atmospheric conditions. In this work, we established a new method that combined laboratory simulation and field observation, which quantified the urban-lifestyle SOA with high time resolution under the real atmospheric condition. The complex SOA was measured and resolved by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). The multilinear engine model (ME-2) and multilinear correction methods were used to apply laboratory results into ambient SOA apportionment. It was found that the vehicle source dominated the SOA formation during the diurnal photochemical process, and the SOA:POA ratio of vehicle source was about 1.4 times larger than that of cooking source. The vehicle emission may undergo an alcohol/peroxide & carboxylic acid oxidation pathway and form higher oxidized SOA, while the cooking emission may undergo an alcohol/peroxide oxidation pathway and form relatively lower oxidized SOA. The vehicle SOA and cooking SOA contributed 45.6 % and 24.8 % of OA during a local episode in 2021 winter of downtown Beijing. Our findings could not only provide a new way to quantify urban SOA but also demonstrate some laboratory hypotheses, conducing to understand its ambient contributions, chemical features, and environmental effects.

Chemically Oscillating Reactions during the Diagenetic Formation of Ediacaran Siliceous and Carbonate Botryoids

Chemically oscillating reactions are abiotic reactions that produce characteristic, periodic patterns during the oxidation of carboxylic acids. They have been proposed to occur during the early diagenesis of sediments that contain organic matter and to partly explain the patterns of some enigmatic spheroids in malachite, phosphorite, jasper chert, and stromatolitic chert from the rock record. In this work, circularly concentric self-similar patterns are shown to form in new chemically oscillating reaction experiments with variable mixtures of carboxylic acids and colloidal silica. This is carried out to best simulate in vitro the diagenetic formation of botryoidal quartz and carbonate in two Ediacaran-age geological formations deposited after the Marinoan–Nantuo snowball Earth event in South China. Experiments performed with alkaline colloidal silica (pH of 12) show that this compound directly participates in pattern formation, whereas those with humic acid particles did not. These experiments are particularly noteworthy since they show that pattern formation is not inhibited by strong pH gradients, since the classical Belousov–Zhabotinsky reaction occurs in solution with a pH around 2. Our documentation of hundreds of classical Belousov–Zhabotinsky experiments yields a number of self-similar patterns akin to those in concretionary structures after the Marinoan–Nantuo snowball Earth event. Morphological, compositional, and size dimensional comparisons are thus established between patterns from these experiments and in botryoidal quartz and carbonate from the Doushantuo and Denying formations. Selected specimens exhibit circularly concentric layers and disseminations of organic matter in quartz and carbonate, which also occurs in association with sub-micron-size pyrite and sub-millimetre iron oxides within these patterns. X-ray absorption near edge structure (XANES) analyses of organic matter extracted from dolomite concretions in slightly younger, early Cambrian Niutitang Formation reveal the presence of carboxylic and N-bearing molecular functional groups. Such mineral assemblages, patterns, and compositions collectively suggest that diagenetic redox reactions take place during the abiotic decay of biomass, and that they involve Fe, sulphate, and organic matter, similarly to the pattern-forming experiments. It is concluded that chemically oscillating reactions are at least partly responsible for the formation of diagenetic siliceous spheroids and concretionary carbonate, which can relate to various other persistent problems in Earth and planetary sciences.

Hydrothermal One-Electron Oxidation of Carboxylic Acids in the Presence of Iron Oxide Minerals

Hydrothermal One-Electron Oxidation of Carboxylic Acids in the Presence of Iron Oxide Minerals

Modeling the photocatalytic oxidation of carboxylic acids on aqueous TiO2 suspensions and on immobilized TiO2-chitosan thin films in different reactor geometries irradiated by UVA or UVC light sources

Photocatalytic reactor models incorporating radiation transport parameters and intrinsic kinetic parameters of photocatalytic decomposition of single-compound and mixtures of oxalic (OA) and formic acid (FA), in both slurry suspensions and immobilized photocatalytic thin films, were validated in two well-mixed annular photoreactors geometries irradiated with either UVA or UVC radiation. The six-flux absorption scattering model (SFM) predicted the radiation field in a titanium dioxide (TiO2 P25) catalyst suspension, the local volumetric rate of photon absorption (LVRPA) at each point of the reactor and, after volumetric integration, the lumped VRPA. The model combining the lumped VRPA, the kinetics models describing the adsorption and photocatalytic decomposition of OA and FA and the material balance of the reacting species was fitted to the experimental results of photocatalytic decomposition of OA and FO in a slurry TiO2 suspension, to determine the OA and FA intrinsic reaction kinetics parameters. Such intrinsic parameters were then used with the average surface rate of photon absorption (SRPA) to model and predict the photocatalytic oxidation of OA and FA on non-porous TiO2–chitosan films immobilized on glass plates immersed in the photoreactor. The models for both slurry suspensions and immobilized photocatalysts predicted the degradation and mineralization of OA and FA and of a mixture of them under diverse experimental conditions. This study demonstrates a systematic methodology for determining intrinsic reaction kinetics rate parameters of water contaminants that can also be used to represent the photocatalytic oxidation of such contaminants in irradiated slurries and in immobilized photocatalytic thin films and in any photoreactor geometry.

Organic synthesis via Kolbe and related non-Kolbe electrolysis: an enabling electro-strategy

Herein, the electrolysis process, where the anodic oxidation of carboxylic acids leads to decarboxylation, has been discussed to synthesize organic molecules.

Catalytic enantioselective synthesis of 1,4-dihydropyridines via the addition of C(1)-ammonium enolates to pyridinium salts.

The regio- and stereoselective addition of C(1)-ammonium enolates – generated in situ from aryl esters and the isothiourea catalyst (R)-BTM – to pyridinium salts bearing an electron withdrawing substituent in the 3-position allows the synthesis of a range of enantioenriched 1,4-dihydropyridines. This represents the first organocatalytic approach to pyridine dearomatisation using pronucleophiles at the carboxylic acid oxidation level. Optimisation studies revealed a significant solvent dependency upon product enantioselectivity, with only toluene providing significant asymmetric induction. Using DABCO as a base also proved beneficial for product enantioselectivity, while investigations into the nature of the counterion showed that co-ordinating bromide or chloride substrates led to higher product er than the corresponding tetrafluoroborate or hexafluorophosphate. The scope and limitations of this process are developed, with enantioselective addition to 3-cyano- or 3-sulfonylpyridinium salts giving the corresponding 1,4-dihydropyridines (15 examples, up to 95 : 5 dr and 98 : 2 er).

N-Alkylation of Hetarenes through Electrochemical Oxidation of Carboxylic Acids

N-Alkylation of Hetarenes through Electrochemical Oxidation of Carboxylic Acids

Photo-NHC Catalysis: Accessing Ketone Photochemistry with Carboxylic Acid Derivatives

AbstractExcitation of carbonyl groups is one of the most widely employed activation modes in photochemistry. Many synthetically important transformations, however, are successful only with aldehydes and ketones; substrates at the carboxylic acid oxidation level remain underrepresented. We have developed a conceptually novel strategy for enabling ‘ketone-like’ photochemistry with carboxylic acid derivatives that employs an N-heterocyclic carbene (NHC) organocatalyst. Using this ‘Photo-NHC’ catalysis approach, a proof-of-concept photoenolization/Diels–Alder (PEDA) reaction between acid fluorides and trifluoroacetophenones was developed. Stoichiometric studies and TD-DFT calculations supported a mechanistic scenario in which the NHC influences the absorption wavelength and inherent photochemical reactivity of the carbonyl group during the catalytic cycle.1 Introduction2 Photo-NHC Catalysis3 Conclusions

Synthesis of CdS Nanoparticles by Electrochemical Method: Correlation for Photodegradation of Trichloroacetic Acid, Chloroacetic Acid, Acetic Acid and Antibacterial Efficiency

Cadmium sulfide (CdS) nanoparticle has been successfully synthesized by electrochemical method which is simple and inexpensive method. The synthesized CdS nanoparticles were used as a catalyst for the photodegradation of trichloroacetic acid, chloroacetic acid and acetic acid under various experimental conditions by volumetric method. The CdS nanoparticles were characterized by various techniques such as SEM-EDAX, UV-Visible spectroscopy, FTIR-IR spectrum and X-ray diffraction studies. The study of UV-Visible spectroscopy revealed that the CdS nanoparticles showed that the maximum intensity peak at 253.64 nm in the UV-region and the band gap energy is found to be 2.39 nm which was calculated using Tauc-plot. The SEM results showed that the CdS nanoparticles have spherical shape. The EDAX spectra revels the presence of Cd and S in the nanoparticles. From XRD data, the structure of CdS nanoparticles was found to be cubic structure and crystallite size was found to be 16.10 nm. The photocatalytic activity of the synthesized CdS nanoparticles was investigated by the kinetics of photodegradation of carboxylic acids by volumetric method by using NaOH solution. Taft LFER was tested, the isokinetic temperature β was calculated for oxidation of carboxylic acids. The antibacterial activity of CdS nanoparticles was investigated by using gram positive (<i>Bacillus subtilis </i>MTCC 2763) and gram negative (<i>Escherichia coli </i>MTCC 40) bacteria by disc diffusion Kirby-Bauer method in Mueller Hinton Agar Plate by determining the ZOI.<div><br></div>

Electrosynthesis Using Carboxylic Acid Derivatives: New Tricks for Old Reactions.

Electrosynthetic organic chemistry is an old discipline that takes its root in Faraday's seminal works. The field has a rich history and is in the midst of a renaissance, due to the growing impetus of the chemical community to develop greener, more economical, and more efficient synthetic methodologies. Indeed, electrosynthesis relies on one of the greenest and cheapest reagents in the world: the electron itself. In this Account, the recent developments in the use of carboxylic acid derivatives in electrosynthesis are summarized. Until lately, the fate of the monoelectronic reduction of aromatic esters in nonprotic solvents remained unclear. Recent investigations have shown that aromatic esters are reduced and form surprisingly long-lived radical anions. Under the right conditions, these radical anions decompose into the corresponding carboxylates and alkyl radicals. These principles have been used to develop a novel electrochemical alcohol deoxygenation reaction using aromatic esters as stable and versatile radical precursors. In contrast to esters, the electrochemistry of carboxylic acids has been intensively studied. Pioneering works by Faraday and Kolbe in the late 1800s have revealed that the anodic oxidation of carboxylic acids leads to a radical decarboxylation. Interestingly, radical recombination is observed due to the very high concentration of radicals in the vicinity of the electrode. Such radical recombination is rarely observed during classical homogeneous radical reactions. The "Kolbe" reaction and its carbocationic variation have been intensively used across the fields due to their versatility. As we will develop in this Account, almost two hundred years after its discovery, the anodic decarboxylation of carboxylic acids is still relevant to modern organic chemists. For instance, we will examine how the non-decarboxylate Kolbe reaction of aromatic acids forms aroyloxy radicals and how oxycarbonyl radicals could be generated from hemioxalates. Finally, the carbocationic variant of the Kolbe reaction, known as the Hofer-Moest reaction, will be examined in the context of two newly developed reactions: a green MOM-type ether formation and the use of malonic acid derivatives as carbonyl synthons. Electrosynthesis is a powerful synthetic tool. Even if it might still be underutilized at the moment, there is little doubt that it will become one of the "classic" methods to activate small organic molecules in a very near future.

Correlation for Photocatalytic Degradation Kinetics of Carboxylic Acids using Electrochemically Synthesized Al2S3 Nanoparticles and Study of Antibacterial Activity

Aluminium sulfide (Al2S3) nanoparticles were successfully synthesized by electrochemical method. Further, the synthesized nanoparticles were used as a photocatalyst for degradation of trichloroacetic acid, chloroacetic acid, acetic acid and degradation kinetics was studied by volumetric method using NaOH under various experimental conditions. The Al2S3 nanoparticles were characterized by UV-visible spectroscopy, X-ray diffraction and SEM-EDAX. The study of UV-visible spectroscopy indicates that Al2S3 nanoparticles shows maximum intensity peak at 222 nm in the UV region and there is no absorption peak in the visible region, therefore the synthesized nanoparticles is active under UV light and band gap energy was found to be 3.07 eV, which was calculated using Tauc plot. The structure of Al2S3 was found to be tetragonal structure and average crystal size was found to be 25.76 nm, which was calculated using Debye-Scherrer′s formula. The SEM results showed that Al2S3 appears as nanoflakes with agglomerated. The presence of aluminium and sulfur was confirmed using EDAX spectra. The photocatalytic activity of the synthesized Al2S3 nanoparticles was examined by taking three carboxylic acids by volumetric method. Taft LFER was tested, the isokinetic temperature β was calculated for oxidation of carboxylic acids. The antibacterial activity was investigated for synthesized nanoparticles by using Bacillus subtilis MTCC 2763 and Escherichia coli MTCC 40 of different bacteria.

Synthesis of Cadmium Oxide Nanoparticles by Electrochemical Method: Its Photodegradative Effects on Carboxylic Acids and Antibacterial Behaviours

Cadmium oxide (CdO) nanomaterial has been synthesized by electrochemical method which is simple and inexpensive method. The synthesized cadmium oxide nanomaterial was used as a catalyst for the photocatalytic degradation of acetic acid, formic acid and oxalic acids under varies experimental conditions by volumetric method. The synthesized nanomaterials were characterized by various techniques such as UV-Visible spectroscopy, SEM-EDAX, FT-IR spectrum and X-ray diffraction studies. The UV-VIS spectroscopy study revealed that the band gap energy of cadmium oxide nanomaterials to be 2. 85 eV Tauc plot. The structure of cadmium oxide was found to be cubic structure and crystal size was found to be 32 nm which was confirmed from XRD data. SEM reports showed that the cadmium oxide nanomaterials have regular spherical shape and uniform size. The presence of cadmium and oxygen in the nanomaterial is confirmed from the EDAX spectrum. FT-IR spectra reveal the presence of characteristic band corresponds to Cd-O mode. The photocatalytic activity of the synthesized cadmium oxide nanomaterial was examined by the kinetics of photodegradation of carboxylic acids by volumetric method by using NaOH solution. Taft LFER was tested the isokinetic temperature β was calculated for oxidation of carboxylic acids. The antibacterial activity of cadmium oxide nanomaterial was investigated.<div><br></div>

A first evaluation of butanoic and pentanoic acid oxidation kinetics

Despite the recent interest in large carboxylic acid oxidation due to their presence in pyrolysis bio-oils, their kinetics of pyrolysis and oxidation has not been experimentally addressed. For the first time, this paper reports a new set of experimental data for the oxidation in a jet-stirred reactor of two high molecular weight carboxylic acids: butanoic (butyric) and pentanoic (valeric) acids. This work was performed at 106.7 kPa (800 Torr) over a range of temperatures from 800 to 1100 K. The experiments were carried out under highly diluted conditions (inlet fuel mole fraction of 0.005) for three equivalence ratios: 0.5, 1 and 2. During this study a wide range of products has been identified and quantified from CO and CO2 to C5 species: 36 for pentanoic acid and 18 for butanoic acid. An interpretative kinetic model has been developed based on a recent theoretical study on the pyrolysis and oxidation of acetic acid (Cavalotti et al. PROCI, 37 (2019) 539–546) and on alkane rate rules (Ranzi et al. Combust. Flame, 162 (2015) 1679–1691). This new kinetic subset has been implemented in the CRECK kinetic framework covering the pyrolysis and oxidation of molecules from syngas up to heavy fuels, including PAHs formation. The mole fractions of fuel and product species were compared with results from model simulations over the experimental temperature range, providing reasonable agreement. A flow rate analysis allowed a better understanding of the most important degradation pathways of these acids, including a small contribution of low-temperature oxidation channels.

Decarboxylative Cyanation of Aliphatic Carboxylic Acids via Visible-Light Flavin Photocatalysis.

An operationally simple method is disclosed for the decarboxylative cyanation of aliphatic carboxylic acids at room temperature. Riboflavin tetraacetate, which is an inexpensive organic photocatalyst, promotes the oxidation of carboxylic acids upon visible-light activation. After decarboxylation, the generated radicals are trapped by TsCN, yielding the desired nitriles without any further additive, in a redox-neutral process. Importantly, this protocol can be adapted to flow conditions.

Amine hemilability enables boron to mechanistically resemble either hydride or proton.

Tetracoordinate MIDA (N-methyliminodiacetic acid) boronates have found broad utility in chemical synthesis. Here, we describe mechanistic insights into the migratory aptitude of the MIDA boryl group in boron transfer processes, and show that the hemilability of the nitrogen atom on the MIDA ligand enables boron to mechanistically resemble either a hydride or a proton. The first case involves a 1,2-boryl shift, in which boron migrates as a nucleophile in its tetracoordinate form. The second case involves a neighbouring atom-promoted 1,4-boryl shift, in which boron migrates as an electrophile in its pseudo-tricoordinate form. Density functional theory studies and in situ NMR measurements all suggest that MIDA can act as a dynamic switch. These findings encouraged the development of novel migration processes involving boron that exploit the chameleonic behaviour of boron by acting as both a nucleophile and an electrophile, including the first report of a compound with a boronate functionality bound to carbon in the carboxylic acid oxidation state.

Molecular control of gene expression by Brucella BaaR, an IclR-type transcriptional repressor

The general stress response sigma factor σE1 directly and indirectly regulates the transcription of dozens of genes that influence stress survival and host infection in the zoonotic pathogen Brucella abortus Characterizing the functions of σE1-regulated genes therefore would contribute to our understanding of B. abortus physiology and infection biology. σE1 indirectly activates transcription of the IclR family regulator Bab2_0215, but the function of this regulator remains undefined. Here, we present a structural and functional characterization of Bab2_0215, which we have named B rucella adipic acid-activated regulator (BaaR). We found that BaaR adopts a classic IclR-family fold and directly represses the transcription of two operons with predicted roles in carboxylic acid oxidation. BaaR binds two sites on chromosome II between baaR and a divergently transcribed hydratase/dehydrogenase (acaD2), and it represses transcription of both genes. We identified three carboxylic acids (adipic acid, tetradecanedioic acid, and ϵ-aminocaproic acid) and a lactone (ϵ-caprolactone) that enhance transcription from the baaR and acaD2 promoters. However, neither the activating acids nor caprolactone enhanced transcription by binding directly to BaaR. Induction of baaR transcription by adipic acid required the gene bab2_0213, which encodes a major facilitator superfamily transporter, suggesting that Bab2_0213 transports adipic acid across the inner membrane. We conclude that a suite of structurally related organic molecules activate transcription of genes repressed by BaaR. Our study provides molecular-level understanding of a gene expression program in B. abortus that is downstream of σE1.

Aerosol Fragmentation Driven by Coupling of Acid-Base and Free-Radical Chemistry in the Heterogeneous Oxidation of Aqueous Citric Acid by OH Radicals.

A key uncertainty in the heterogeneous oxidation of carboxylic acids by hydroxyl radicals (OH) in aqueous-phase aerosol is how the free-radical reaction pathways might be altered by acid-base chemistry. In particular, if acid-base reactions occur concurrently with acyloxy radical formation and unimolecular decomposition of alkoxy radicals, there is a possibility that differences in reaction pathways impact the partitioning of organic carbon between the gas and aqueous phases. To examine these questions, a kinetic model is developed for the OH-initiated oxidation of citric acid aerosol at high relative humidity. The reaction scheme, containing both free-radical and acid-base elementary reaction steps with physically validated rate coefficients, accurately predicts the experimentally observed molecular composition, particle size, and average elemental composition of the aerosol upon oxidation. The difference between the two reaction channels centers on the reactivity of carboxylic acid groups. Free-radical reactions mainly add functional groups to the carbon skeleton of neutral citric acid, because carboxylic acid moieties deactivate the unimolecular fragmentation of alkoxy radicals. In contrast, the conjugate carboxylate groups originating from acid-base equilibria activate both acyloxy radical formation and carbon-carbon bond scission of alkoxy radicals, leading to the formation of low molecular weight, highly oxidized products such as oxalic and mesoxalic acid. Subsequent hydration of carbonyl groups in the oxidized products increases the aerosol hygroscopicity and accelerates the substantial water uptake and volume growth that accompany oxidation. These results frame the oxidative lifecycle of atmospheric aerosol: it is governed by feedbacks between reactions that first increase the particle oxidation state, then eventually promote water uptake and acid-base chemistry. When coupled to free-radical reactions, acid-base channels lead to formation of low molecular weight gas-phase reaction products and decreasing particle size.