Presence Of Carboxylic Acids Research Articles

Addition of triphenylphosphine to electron-deficient alkenes in mixed binary solvents: Overcoming the problem of preferential solvation to determine the reaction order with respect to protic solvent

Kinetics of addition of PPh3 to electron-deficient alkenes has been studied in aprotic solvent+carboxylic acid binary mixtures as a function of the alkene and carboxylic acid concentrations. For ethyl acetate+acetic acid, ethyl acetate+propionic acid, butyl acetate+acetic acid, butyl acetate+propionic acid mixtures, the reactions of PPh3 with acrylic acid and methyl acrylate show no preferential solvation and follow third-order kinetics, first order in the phosphine, the activated alkene, and acetic (propionic) acid. Other alkene/solvent combinations tested also displayed acceleration in the presence of carboxylic acid, but the total effect of the acidic solvent concentration on the reaction rate was nonlinear due to occurrence of preferential solvation. The acid dependence gives the direct evidence for the rate-determining protonation of intermediate phosphonium enolate zwitterion under acidic solvent condition. Since proton transfers from protic solvents are typically fast, the kinetic data obtained give a new mechanistic insight into chemistry of phosphonium enolates: their decomposition to the reactants proceeds much faster than proton transfer step in acidic media. This unexpected finding emphasizes very short lifetime of phosphonium enolates, key intermediates of synthetically useful phosphine-catalyzed reactions.

Effect of Carboxylic Acid (Benzene Crystallable) in Cement Concrete and Geopolymer Concrete

The present study appraises the recitals of carboxylic acid- based admixture to increase concrete water tightness and self-sealing capacity of the cement and geopolymer concrete. Outcomes of the previous studies in particular, adding 1% by cement mass of the carboxylic polymer reasons for reduction in the water dispersion under pressure of 7-day wet cured concrete by 50% associated to that of the conforming reference concrete. At 7 days, M4 mix compressive strength is about 43.5% less than M3 mix. The compressive strength of M4 increases and is about 37.6% less than M3 mix at 28 days of curing. At 7 days, M4 mix split tensile strength is about 17.5% less than M3 mix (cement concrete with 0.45 w/c ratio). The split tensile strength of M4 declines and is about 42.3% less than M3 mix at 28 days of curing. The strength of the geopolymer concrete tends to increase as the time period increases due to the presence of fly ash in it. So it is expected that geopolymer concrete will give more strength than cement concrete in long term with the presence of carboxylic acid.

Methyl ketones from carboxylic acids as valuable target molecules in the biorefinery

For the preparation of methyl ketones, cross Ketonic Decarboxylation, i.e., the formation of a ketone from two different carboxylic acids, and the reketonization, i.e., the transformation of a carboxylic acid into a ketone employing a ketone as alkyl transfer agent, may be interesting alternatives to classical pathways involving metal-organic reagents.The fine chemical 2-undecanone was chosen as model compound and ketonic decarboxylation and reketonization evaluated by Green Chemistry matrices, namely the carbon atom efficiency and the e-factor. The e-factor of the reaction of decanoic acid with acetic acid was less than five and, therewith, in the acceptable range for bulk chemicals, when valorizing acetone (e.g., as a solvent) and considering a 90% solvent recycling. The reketonization of decanoic acid with acetone provided a different main product, namely 10-nonadecanone, with a detrimental effect on atom efficiency.By means of labeling experiments it was shown that ketonic decarboxylation is significantly faster than the reketonization reaction. The transformation of acetic acid into acetone was studied by in-situ and operando IR spectroscopy. Thereby it was found that the surface was covered by acetic acid. The lack of adsorption of acetone is a clear drawback for the reketonization of carboxylic acids. To improve the reaction outcome, and therewith, its sustainability a possibility has to be found to stabilize the ketone molecules on the surface in the presence of carboxylic acids.

The efficient synthesis of 3‐[6‐(substituted)‐[1,2,4]triazolo[3,4‐b][1,3,4]thiadiazol‐3‐yl]‐1H‐indazole

AbstractThis study presents an efficient synthesis of 3‐[6‐(substituted‐phenyl)‐[1,2,4]triazolo[3,4‐b][1,3,4] thiadiazol‐3‐yl]‐1H‐indazole via dehydrative condensation with cyclization of 4‐amino‐5‐(1H‐indazol‐3‐yl)‐4H‐[1,2,4]triazole‐3‐thiol and fluorinated or nonfluorinated carboxylic acids in presence of phosphorous oxychloride. The multistep reaction pathway proceeds through different compounds. Present synthesis has the advantages of easily accessible starting materials, convenient synthesis, simple reaction condition, wider substrate scope, and higher yield (75% to 90% isolated).

The Unified Mechanism of Corrosion in Aqueous Weak Acids Solutions: A Review of the Recent Developments in Mechanistic Understandings of Mild Steel Corrosion in the Presence of Carboxylic Acids, Carbon Dioxide, and Hydrogen Sulfide

The recent developments in mechanistic understandings of mild steel corrosion in the presence of carboxylic acids, carbon dioxide, and hydrogen sulfide, when place side by side, reveal a simple, universal mechanism despite all the differences conventionally presumed for these corroding systems. These findings are recast into a generic mechanistic view of corrosion in aqueous weak acid solutions herein. In this mechanism, the buffering effect resulting from the chemical dissociation reaction inside the boundary layer, is highlighted as an inherent property of all weak acids. The validity of this mechanism was further examined through mathematical experimentation based on a comprehensive mechanistic model. It is shown that this mechanism is able to account for a wide range of characteristic behavior of cathodic currents, including those previously associated with the direct reduction reactions. The results are ultimately presented as a simple and generic categorization of weak acids based on their pKa values to serve as a basis to assess the detrimental effect of any weak acid on mild steel corrosion in aqueous acidic solutions.

High-Spin Mn(V)-Oxo Intermediate in Nonheme Manganese Complex-Catalyzed Alkane Hydroxylation Reaction: Experimental and Theoretical Approach.

Mononuclear nonheme manganese complexes are highly efficient catalysts in the catalytic oxidation of hydrocarbons by hydrogen peroxide in the presence of carboxylic acids. Although high-valent Mn(V)-oxo complexes have been proposed as the active oxidants that afford high regio-, stereo-, and enantioselectivities in the catalytic oxidation reactions, the importance of the spin state (e.g., S = 0 or 1) of the proposed Mn(V)-oxo species is an area that requires further study. In the present study, we have theoretically demonstrated that a mononuclear nonheme Mn(V)-oxo species with an S = 1 ground spin state is the active oxidant that effects the stereo- and enantioselective alkane hydroxylation reaction; it is noted that synthetic octahedral Mn(V)-oxo complexes, characterized spectroscopically and/or structurally, possess an S = 0 spin state and are sluggish oxidants. In an experimental approach, we have investigated the catalytic hydroxylation of alkanes by a mononuclear nonheme Mn(II) complex, [(S-PMB)MnII]2+, and H2O2 in the presence of carboxylic acids; alcohol is the major product with high stereo- and enantioselectivities. A synthetic Mn(IV)-oxo complex, [(S-PMB)MnIV(O)]2+, is inactive in C-H bond activation reactions, ruling out the Mn(IV)-oxo species as an active oxidant. DFT calculations have shown that a Mn(V)-oxo species with an S = 1 spin state, [(S-PMB)MnV(O)(OAc)]2+, is highly reactive and capable of oxygenating the C-H bond via oxygen rebound mechanism; we propose that the triplet spin state of the Mn(V)-oxo species results from the consequence of breaking the equatorial symmetry due to the binding of an equatorial oxygen from an acetate ligand. Thus, the present study reports that, different from the previously reported S = 0 Mn(V)-oxo species, Mn(V)-oxo species with a triplet ground spin state are highly reactive oxidants that are responsible for the regio-, stereo-, and enantioselectivities in the catalytic hydroxylation of alkanes by mononuclear nonheme manganese complexes and terminal oxidants.

On the impact of a phosphoryl group in the recognition capabilities of 2-aminopyridines toward carboxylic acids

Inspired by natural molecular recognition processes, many research efforts have been routed in recent years toward the design of new host–guest molecular systems based on non-covalent interactions. Within this field, 2-aminopyridines (2APs) have been widely studied due to their tunable spectroscopic response in the presence of carboxylic acids. Herein, we present and analyze a novel family of 2AP core compounds based on 2-phosphorylamidopyridine (2PAP). Linear response time-dependent density functional theory (TD-DFT) has been used to characterize and model several spectroscopic properties of 2PAP. Our results, validated through experiments, show that TD-DFT can provide a reliable description of the electronic excited states of these aromatic systems. In addition, we have also studied the amino–imino tautomerization of 2AP and 2PAP in light of TD-DFT tools. We show that the presence of a carboxylic acid has a catalytic effect on the tautomerization reaction, which otherwise does not occur spontaneously at room temperature. These results suggest that this low-cost computational approach can be applied to more complex organic systems derived from 2-aminopyridine, paving the way for the development of potentially useful sensing materials and organic species for molecular recognition.

Extraction of Monocarboxylic Acids from Diluted Solutions with Polyethylene Glycol

An aqueous two-phase system based on polyethylene glycol-1500 and sodium sulfate for the extraction of a number of monocarboxylic acids from aqueous solutions has been studied. The influence of the phase contact time, system composition, the molecular weight of the polymer, and temperature on the quantitative characteristics of the interphase distribution of a number of aliphatic monocarboxylic acids has been investigated. Based on the results, it is concluded that these systems are effective for solving problems of the extraction, separation, and purification of carboxylic acids and they are promising as extraction systems for the extraction of metal salts in the presence of carboxylic acids.

N‐Doped Carbon Wrapped Polyoxometalate Derived from POM‐IL Hybrid: A Heterogeneous Catalyst for the Synthesis of Coumarin Derivatives under Solvent‐Free Conditions

Vanadium substituted Keggin type polyoxometalate loaded N‐doped carbon was prepared from polyoxometalate ionic liquid hybrid by carbonization process. The decomposition of organic part generates various functional groups leaving polyoxometalate part intact. The catalyst was characterized by elemental analysis, FTIR, MAS 13C NMR, XPS and electron microscopy studies. The presence of carboxylic acids, aromatic and hetero‐aromatic groups in the catalyst was confirmed by 13C NMR. The high resolution C1s and O1s XPS analysis further confirmed the presence of these groups. Various oxidation states of nitrogen were confirmed by deconvoluted N1s XPS spectra. Pyridine adsorption study confirms the presence of Bronsted and Lewis acid sites in the catalyst. Layered structure of the catalyst was confirmed by HR TEM analysis. The hybrid material displayed excellent catalytic activity towards the synthesis of coumarin derivatives under solvent‐free conditions.

Immunoregulatory activity of polysaccharides from Tanyang Congou black tea on H22 tumor-bearing mice

In this paper, the polysaccharides from Tanyang Congou black tea were extracted, and their preliminary structural characteristics and in vivo antitumor activity were further investigated. Component and monosaccharides analysis showed that the polysaccharides contained 76.26% of total sugar and 30.24% of uronic acid, and were composed of arabinose, galacturonic acid, galactose, rhamnose, glucose and fucose with their ratio of 34.41:29.68:13.23:4.11:13.68:4.89. FTIR results also indicated the presence of carboxylic acid and pyranose rings. The in vivo antitumor results showed that the black tea polysaccharides could significantly inhibit the growth of H22 tumors with the inhibitory ratios of 50.3% (500 mg/kg) and 66.3% (1000 mg/kg), and effectively protect the thymus and spleen of tumor-bearing mice, promote the immunoregulatory activities of macrophagocytes, NK cells and lymphocytes, and improve IL-2, IFN-γ and TNF-α levels, finally leading to the inhibitory effects on the growth of H22 solid tumors. These results support potential uses of black tea polysaccharides as natural anti-tumor agents and provide a theoretical basis for further development and application of Tanyang Congou black tea in functional food and nutra-pharmaceutical industries.

Metal-Ligand Cooperative C-H Bond Formation by Cyclopentadienone Platinum Complexes.

C-H bond cleavage and formation is one of the most essential elementary reactions in organic chemistry. Herein, a heterolytic sp3 C-H bond reductive elimination from hydroxyCp dimethylplatinum(IV) B is reported. Protonation of cyclopentadienone dimethylplatinum(II) A afforded B via the protonation of the ligand. Successive C-H bond formation from the C anion of the methyl group and the H cation of the hydroxyCp group was observed in the presence of carboxylic acids or hydrogen chloride. The reaction was accompanied by the concurrent reduction of Pt(IV) to Pt(II). Experimental and theoretical investigations suggested that the mechanism for the C-H bond formation was acid-mediated metal-ligand cooperative outer-sphere reductive elimination.

Chemo-enzymatic oxidation of tall oil fatty acids as a precursor for further polyol production

A second generation renewable raw material – tall oil, which is a by-product of the cellulose pulping, was valorised for polyol precursor synthesis. Tall oil fatty acids were epoxidized by in-situ generation of peroxy carboxylic acids in presence of immobilized lipase catalyst – Novozym® 435. The described epoxidation was carried out at milder conditions (40 °C) than typical epoxidation. No organic solvents and no additional carboxylic acids were used for proposed process. Relatively high yields of epoxide oxygen content were achieved (i.e. 4.49–6.00%). The influence of molar ratios between ethylenic unsaturation and hydrogen peroxide (1.0/1.0–1.2), Novozym® 435 catalyst content (1.5–4.5%) and hydrogen peroxide concentration (15–35%) on the epoxidation process were investigated. The epoxidation process was monitored by the change of the relative oxirane conversion and ethylenic unsaturation. The change of the chemical structure of the epoxidized tall oil was investigated using FTIR spectroscopy.

Facile preparation of fluorescent carbon dots for label-free detection of Fe3+

Cellulose is the most abundant biomass resource and use of cellulose in the synthesis of novel nanomaterials like carbon dots (CDs) has gained attention over the years. However, the photoluminescence yield of cellulose-based CDs is low in the absence of modification additives. Durian shell waste (DSW) is a cellulose rich source and is used for the first time in a one-pot process without any modification agent to produce CDs. The presence of carboxylic acids, esters and amino compounds in durian shell was crucial to improving the CD surface and resulting in a mass yield of 13.9% and quantum yield of 6.2%. This was two times higher compared to that of CDs derived from pure cellulose precursors. The blue-green emitting CDs showed stability over a wide range of pH and chloride concentration and was resistant to photobleaching. Further, the CDs showed high selectivity towards Fe3+ by forming a non-fluorescent ground complex with the oxygen functional groups. Based on the linear relationship between normalized fluorescence intensity and concentration of Fe3+ ions, the synthesised CDs may be used as a fluorescent probe to detect Fe3+ over a concentration range of 0–20 μM with a detection limit of 128 nM. The method was successfully applied in sensing Fe3+ in actual water systems.

Bioinspired manganese complexes catalyzed epoxidation for the synthesis of the epoxyketone fragment of carfilzomib

We report herein an efficient catalytic epoxidation reaction for the synthesis of epoxyketone (tert-butyl ((S)-4-methyl-1-((R)-2-methyloxiran-2-yl)-1-oxopentan-2-yl)carbamate), which is an important synthetic intermediate of carfilzomib. A series of bioinspired manganese complexes bearing N4 ligands are carefully investigated in the epoxidation of enone precursor with H2O2 as oxidant in the presence of carboxylic acid (e.g., acetic acid).

(Invited) Hydrogen Bonding Effects at the Organic-Water Interface of Aqueous Toluene Droplets Investigated By Particle Collision Electrochemistry

This work reports on the hydrogen bonding effects induced by water solvation in aqueous toluene droplets studied by Particle Collision Electrochemistry (PCE). The latter approach is an emerging methodology employed to characterize microscopic particles that collide with the surface of an ultramicroelectrode as a result of Brownian motion. The ability of PCE to yield in-situ kinetic and thermodynamic information from single collision events has led to fundamental studies of nanoparticle electrochemistry which now is recognized as a sub-field in electrochemistry dubbed as single entity electrochemistry, due to the wide range of probes that can be investigated. Herein, the reversal of hydrogen bonding affinity between quinone phenolate di-anions (Q2-) and carboxylic acids, induced by water in micrometer-size droplets of toluene is reported. Such an effect is revealed by the two-electron reduction of the hydrophobic quinone (Q) tetrachoro-1,4-benzoquinone to Q2- inside the toluene droplets, when performed in the presence of carboxylic acids that partition differently between the aqueous and organic phases. In bulk toluene, the hydrogen bonding affinity of Q2- for acetic acid (pKa = 4.8) is higher than for oleic acid (pKa = 9.9). However, such trend is reversed in emulsified toluene droplets due to preferential solvation of acetic acid by the surrounding water. The goal of this work is two-fold: first, to illustrate a subtle yet consequential water effect that arises from heterogeneous micro-confinement of organic-water phases, and second, to demonstrate how mechanistic information in such interfaces can be extracted from PCE.

Purification and Characterization of Colophony Extracted of Pinus elliottii (Engelm, var. elliottii)

This study reports the purification and characterization of the colophony. The method involves the step of water washing and solubilization of the extracted resin of Pinus elliottii Emgelm, elliottii variety on ethanol to the filtration for removal of solid residues (sand, leaves, pieces of the branch, etc.). After purification, the colophony and turpentine were separated using a soxhlet extractor. The thermal decomposition of colophony was investigated using thermogravimetric analysis-differential thermogravimetric-differential scanning calorimetry (TG-DTG-DSC). The resin was also characterized using the technique of infrared spectroscopy (ATR-FTIR). The TG curves revealed three decomposition steps, in which a total degradation occurred after 500 °C, indicating a good thermic stability. The FTIR spectrum showed bands in 1694 cm -1 , (stretch C=O) and 3362 cm -1 (stretch O-H) indicating the presence of carboxylic acid, have also been found bands corresponding to the aromatic ring. The presence of resinous acids can be confirmed. DOI: http://dx.doi.org/10.17807/orbital.v10i3.1100

Electrodegradation of naphthalenic amines: Influence of the relative position of the substituent groups, anode material and electrolyte on the degradation products and kinetics

The electrodegradation of the 4-aminonaphthalene-1-sulfonic acid (4AN1S), 5-aminonaphthalene-2-sulfonic acid (5AN2S) and 8-aminonaphthalene-2-sulfonic acid (8AN2S) was studied, using two electrode materials as anode, BDD and Ti/Pt/PbO2, and two different electrolytes, sodium sulfate and sodium chloride. The highest COD removal rates were obtained at BDD: for 5AN2S and 8AN2S results were similar in both electrolytes; for 4AN1S, results were better in sodium chloride. The lowest COD removal rates were obtained at the system Ti/Pt/PbO2-sodium sulfate, for all the studied amines. The dissolved organic carbon (DOC) removal was much higher at BDD for all the amines, in sulfate for 5AN2S and 8AN2S and in chloride for 4AN1S. Nitrogen removal was always almost irrelevant in sulfate medium but higher than 60%, after 6-h assays, in chloride. The highest combustion efficiencies were attained at the system BDD-sodium sulfate and were: 4AN1S-75%; 5AN2S-84%; 8AN2S-74%. HPLC results show that total degradation of the studied aminonaphthalene sulfonates is attained at both anode materials, utilizing any of the electrolytes, with a first order kinetics. However, kinetic constants obtained with the variation of the amines concentration in time are 10–40 times higher in chloride, being slightly higher at Ti/Pt/PbO2 than at BDD. Regarding the presence of carboxylic acids during the degradation assays, it was observed that the electrolysis of the amines 5AN2S and 8AN2S always lead to higher amounts of oxalic acid and lower quantities of acetic acid than the electrolysis of the amine 4AN1S.

Covalent modification of graphitic carbon through in-situ diazonium ion formation and its reduction: A robust pellet electrode as a novel electrochemical interface for divalent lead quantification

Phenyl carboxylic acid functionalized graphitic carbon fabricated pellet electrode has been used as an electrochemical interface for lead(II) quantification. The graphitic carbon has been functionalized through in-situ diazotization process using 2-amino carboxylic acid in presence of hypophosphorous acid as a reducing agent. The native and functionalized graphitic carbon powders were characterized by various spectroscopy techniques such as Fourier transform infrared spectroscopy, Powder-X-ray diffraction, Field emission scanning electron microscope, and Atomic force microscopy. All the above spectroscopic studies revealed the functionalization of graphitic carbon with 2-phenyl carboxylic acid groups. The functionalized graphitic carbon has been compressed into pellet and used as a robust electrode without using any binder. The proposed sensor has been applied for lead(II) ion determination by differential pulse anodic striping voltammetry (DPASV). The proposed sensor exhibited a wide linearity in the concentration range 10–1000 μM. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.256 and 2.45 μM respectively with a relative standard deviation of ±0.97% at 100 μM level concentration. The proposed sensor has been successfully applied to determine lead(II) from a variety of sample matrices including industrial effluents, polluted lake waters and soil sludge samples.

Photoreduction of 4-Nitrophenol in the presence of carboxylic acid using CdS nanofibers

The photocatalytic reduction of 4-Nitrophenol was assisted with blue light irradiation using CdS semiconductor nanofiber. The kinetic study of the blue-photoreduction of 4-Nitrophenol to 4-Aminophenol was performed by using Na2SO3 as “hole scavenger” in the presence of middle carboxylic acids (acetic, oxalic and citric acid). The effect of photocatalyst load, the carboxylic acid concentration and of the pH solution (acid, neutral and alkaline media) were investigated. The maximum 4-Nitrophenol photoreduction rate was reached in neutral media and it is related to the enhanced “hole scavenging” effect caused by the SO32− or HSO32− ions in the presence of carboxylic acid. Electrochemical characterization of CdS nanofiber was made in the presence of 4-NP and citric acid. The 4-NP photoreduction reaction follows a zero order reaction and a possible mechanism to explain the fast electron transfer process is discussed as a consequence of the carboxylic acid adsorbed on the CdS surface.

Robust cobalt oxide catalysts for controllable hydrogenation of carboxylic acids to alcohols

The selective catalytic hydrogenation of carboxylic acids is an important process for alcohol production, while efficient heterogeneous catalyst systems are still being explored. Here, we report the selective hydrogenation of carboxylic acids using earth-abundant cobalt oxides through a reaction-controlled catalysis process. The further reaction of the alcohols is completely hindered by the presence of carboxylic acids in the reaction system. The partial reduction of cobalt oxides by hydrogen at designated temperatures can dramatically enhance the catalytic activity of pristine samples. A wide range of carboxylic acids with a variety of functional groups can be converted to the corresponding alcohols at a yield level applicable to large-scale production. Cobalt monoxide was established as the preferred active phase for the selective hydrogenation of carboxylic acids.