Showing papers on "Carboxylic acid published in 2014"
TL;DR: This work quantifies global emissions of C4-C14 perfluoroalkyl carboxylic acid (PFCA) homologues during the life-cycle of products based on perfluorooctanoic Acid (PFOA), perfLUorononanoic acid (PFNA), perfluarooctane sulfonyl fluoride (POSF), and fluorotelomer compounds, and addresses the uncertainties of the PFCA emissions by defining a lower
507 citations
TL;DR: In-situ removal of carboxylic acid by extraction during fermentation is the most popular approach, but recovery of the extractant can easily lead to waste inorganic salt formation, which counteracts the advantage of the in-Situ removal.
379 citations
TL;DR: In this article, the authors describe the catalytic reduction of amides, carboxylic acid esters and nitriles with homogeneous catalysts using molecular hydrogen as an environmental friendly reducing agent.
298 citations
TL;DR: Preliminary mechanistic studies reveal that a single electron transfer pathway may be involved in the catalytic cycle.
Abstract: The palladium-catalyzed difluoroalkylation of aryl boronic acids with bromodifluoromethylphosphonate, bromodifluoroacetate, and further derivatives has been developed. This method provides a facile and useful access to a series of functionalized difluoromethylated arenes (ArCF2 PO(OEt)2 , ArCF2 CO2 Et, and ArCF2 CONR(1) R(2) ) that have important applications in drug discovery and development. Preliminary mechanistic studies reveal that a single electron transfer (SET) pathway may be involved in the catalytic cycle.
273 citations
TL;DR: This work presents the first base-free Fe-catalyzed ester reduction applying molecular hydrogen, and reveals an outer-sphere mechanism involving simultaneous hydrogen transfer from the iron center and the ligand.
Abstract: We present the first base-free Fe-catalyzed ester reduction applying molecular hydrogen. Without any additives, a variety of carboxylic acid esters and lactones were hydrogenated with high efficiency. Computations reveal an outer-sphere mechanism involving simultaneous hydrogen transfer from the iron center and the ligand. This assumption is supported by NMR experiments.
248 citations
TL;DR: Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism, giving 5-substituted pyridines with very high levels of regioselectivity.
Abstract: α,β-Unsaturated carboxylic acids undergo Rh(III)-catalyzed decarboxylative coupling with α,β-unsaturated O-pivaloyl oximes to provide substituted pyridines in good yield. The carboxylic acid, which is removed by decarboxylation, serves as a traceless activating group, giving 5-substituted pyridines with very high levels of regioselectivity. Mechanistic studies rule out a picolinic acid intermediate, and an isolable rhodium complex sheds further light on the reaction mechanism.
245 citations
TL;DR: Graphene sheets were covalently functionalized with aromatic-aliphatic amino acids (phenylalanine and tyrosine) by simple and green procedure as discussed by the authors, and Amino acid functionalized graphene demonstrates stable dispersion in water and common organic solvents.
158 citations
TL;DR: The amine-functionalized graphene oxide (OFGO) was used as an acid-base bifunctional catalyst in one-pot cascade reactions containing successive acetal hydrolysis and Knoevenagel condensation.
Abstract: The amine-functionalized graphene oxide was prepared by a facile one-step silylation approach and used as an acid–base bifunctional catalyst in one-pot cascade reactions containing successive acetal hydrolysis and Knoevenagel condensation owing to the separate coexistence of original carboxylic acid on the edge of the GO sheet and the postgrafted amine groups on the GO basal surface. This catalyst exhibited much higher activity than either amine-functionalized active carbon, amine-functionalized SBA-15, or amine-functionalized Al2O3 due to the enriched surface acid sites and the diminished diffusion limitation as well as high catalyst dispersion in liquid solution due to the unique two-dimensional structure. More importantly, this catalyst could be easily recycled and used repetitively, showing potential application in industry.
152 citations
TL;DR: UiO-66-AD6 showed the most strongly enhanced CO2 uptake capacity and significantly increased selectivity for CO2 adsorption over that of CH4 at ambient temperature, suggesting that it is a promising material for sequestering CO2 from landfill gas.
Abstract: A series of porous metal-organic frameworks having flexible carboxylic acid pendants in their pores (UiO-66-ADn: n=4, 6, 8, and 10, where n denotes the number of carbons in a pendant) has been synthesized by post-synthetic ligand exchange of terephthalate in UiO-66 with a series of alkanedioic acids (HO2 C(CH2 )n-2 CO2 H). NMR, IR, PXRD, TEM, and mass spectral data have suggested that a terephthalate linker in UiO-66 was substituted by two alkanedioate moieties, resulting in free carboxyl pendants in the pores. When post-synthetically modified UiO-66 was partially digested by adjusting the amount of added HF/sample, NMR spectra indicated that the ratio of alkanedioic acid/terephthalic acid was increased with smaller amounts of acid, implying that the ligand substitution proceeded from the outer layer of the particles. Gas sorption studies indicated that the surface areas and the pore volumes of all UiO-66-ADns were decreased compared to those of UiO-66, and that the CO2 adsorption capacities of UiO-66-ADn (n=4, 8) were similar to that of UiO-66. In the case of UiO-66-AD6, the CO2 uptake capacity was 34 % higher at 298 K and 58 % higher at 323 K compared to those of UiO-66. It was elucidated by thermodynamic calculations that the introduction of flexible carboxyl pendants of appropriate length has two effects: 1) it increases the interaction enthalpy between the host framework and CO2 molecules, and 2) it mitigates the entropy loss upon CO2 adsorption due to the formation of multiple configurations for the interactions between carboxyl groups and CO2 molecules. The ideal adsorption solution theory (IAST) selectivity for CO2 adsorption over that of CH4 was enhanced for all of the UiO-66-ADns compared to that of UiO-66 at 298 K. In particular, UiO-66-AD6 showed the most strongly enhanced CO2 uptake capacity and significantly increased selectivity for CO2 adsorption over that of CH4 at ambient temperature, suggesting that it is a promising material for sequestering CO2 from landfill gas.
124 citations
TL;DR: Antifungal activity of the prepared analogs showed that salicylaldehyde hydrazones and hydrazides are potent inhibitors of fungal growth with little to no mammalian cell toxicity, making these analogs promising new targets for future therapeutic development.
119 citations
TL;DR: A pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification enables direct production of fine chemicals following mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide.
Abstract: Short-chain carboxylates such as acetate are easily produced through mixed culture fermentation of many biological waste streams, although routinely digested to biogas and combusted rather than harvested. We developed a pipeline to extract and upgrade short-chain carboxylates to esters via membrane electrolysis and biphasic esterification. Carboxylate-rich broths are electrolyzed in a cathodic chamber from which anions flux across an anion exchange membrane into an anodic chamber, resulting in a clean acid concentrate with neither solids nor biomass. Next, the aqueous carboxylic acid concentrate reacts with added alcohol in a water-excluding phase to generate volatile esters. In a batch extraction, 96 ± 1.6% of the total acetate was extracted in 48 h from biorefinery thin stillage (5 g L(-1) acetate) at 379 g m(-2) d(-1) (36% Coulombic efficiency). With continuously regenerated thin stillage, the anolyte was concentrated to 14 g/L acetic acid, and converted at 2.64 g (acetate) L(-1) h(-1) in the first hour to ethyl acetate by the addition of excess ethanol and heating to 70 °C, with a final total conversion of 58 ± 3%. This processing pipeline enables direct production of fine chemicals following undefined mixed culture fermentation, embedding carbon in industrial chemicals rather than returning them to the atmosphere as carbon dioxide.
TL;DR: It is found that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride and results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands.
Abstract: We synthesized HfO2 nanocrystals from HfCl4 using a surfactant-free solvothermal process in benzyl alcohol and found that the resulting nanocrystals could be transferred to nonpolar media using a mixture of carboxylic acids and amines. Using solution 1H NMR, FTIR, and elemental analysis, we studied the details of the transfer reaction and the surface chemistry of the resulting sterically stabilized nanocrystals. As-synthesized nanocrystals are charge-stabilized by protons, with chloride acting as the counterion. Treatment with only carboxylic acids does not lead to any binding of ligands to the HfO2 surface. On the other hand, we find that the addition of amines provides the basic environment in which carboxylic acids can dissociate and replace chloride. This results in stable, aggregate-free dispersions of HfO2 nanocrystals, sterically stabilized by carboxylate ligands. Moreover, titrations with deuterated carboxylic acid show that the charge on the carboxylate ligands is balanced by coadsorbed protons. ...
TL;DR: Mixed culture fermentation between the syngas fermenting Alkalibaculum bacchi strain CP15 and propionic acid producer Clostridium propionicum resulted in a 50% higher conversion efficiency of these acids to their respective alcohols compared to CP15 monoculture.
TL;DR: The findings show that in contrast to the originally proposed mechanism, the catalytic cycle involves an intramolecular protonation and not an oxidative insertion of rhodium in the OH bond of the carboxylic acid.
Abstract: Previously we reported the redox-neutral atom economic rhodium catalyzed coupling of terminal alkynes with carboxylic acids using the DPEphos ligand. We herein present a thorough mechanistic investigation applying various spectroscopic and spectrometric methods (NMR, in situ-IR, ESI-MS) in combination with DFT calculations. Our findings show that in contrast to the originally proposed mechanism, the catalytic cycle involves an intramolecular protonation and not an oxidative insertion of rhodium in the OH bond of the carboxylic acid. A σ-allyl complex was identified as the resting state of the catalytic transformation and characterized by X-ray crystallographic analysis. By means of ESI-MS investigations we were able to detect a reactive intermediate of the catalytic cycle.
TL;DR: This reaction represents a novel decarboxylation of an sp(3)-hybridized carbon and the use of a benzylic carboxylic acid as a source of carbonyl compounds.
Abstract: Aromatic aldehydes or ketones from copper catalyzed aerobic oxidative decarboxylation of phenylacetic acids and α-hydroxyphenylacetic acids have been synthesized. This reaction combined decarboxylation, dioxygen activation, and C–H bond oxidation steps in a one-pot protocol with molecular oxygen as the sole terminal oxidant. This reaction represents a novel decarboxylation of an sp3-hybridized carbon and the use of a benzylic carboxylic acid as a source of carbonyl compounds.
TL;DR: The nickel-catalyzed direct carboxylation of alkenes with the cheap and abundantly available C1 building block carbon dioxide (CO2) in the presence of a base has been achieved and it is possible, in one step, to synthesize sodium acrylate from ethylene, CO2 , and a sodium salt.
Abstract: The nickel-catalyzed direct carboxylation of alkenes with the cheap and abundantly available C1 building block carbon dioxide (CO2 ) in the presence of a base has been achieved. The one-pot reaction allows for the direct and selective synthesis of a wide range of α,β-unsaturated carboxylates (TON>100, TOF up to 6 h(-1) , TON=turnover number, TOF=turnover frequency). Thus, it is possible, in one step, to synthesize sodium acrylate from ethylene, CO2 , and a sodium salt. Acrylates are industrially important products, the synthesis of which has hitherto required multiple steps.
TL;DR: A silver-mediated decarboxylative C-S cross-coupling reaction of aliphatic carboxylic acid is described and provides an alternative approach for the synthesis of alkyl aryl sulfides.
TL;DR: In this article, the design of ternary cocrystals based on synthon modularity is described, and the strategy is based on the idea of extending the modularity of 4-hydroxybenzamide and 4-bromobenzamide.
Abstract: Design of ternary cocrystals based on synthon modularity is described. The strategy is based on the idea of extending synthon modularity in binary cocrystals of 4-hydroxybenzamide:dicarboxylic acids and 4-bromobenzamide:dicarboxylic acids. If a system contains an amide group along with other functional groups, one of which is a carboxylic acid group, the amide associates preferentially with the carboxylic acid group to form an acid–amide heterosynthon. If the amide and the acid groups are in different molecules, a higher multicomponent molecular crystal is obtained. This is a stable pattern that can be used to increase the number of components from two to three in a multicomponent system. Accordingly, noncovalent interactions are controlled in the design of ternary cocrystals in a more predictable manner. If a single component crystal with the amide–amide dimer is considered, modularity is retained even after formation of a binary cocrystal with acid–amide dimers. Similarly, when third component halogen a...
TL;DR: A conjugate-base-stabilized Brønsted acid facilitates catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine and enables the formation of β-carbolines with up to 92% ee.
TL;DR: The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organoc atalyst.
Abstract: Two chiral carboxylic acid functionalized micro- and mesoporous metal–organic frameworks (MOFs) are constructed by the stepwise assembly of triple-stranded heptametallic helicates with six carboxylic acid groups. The mesoporous MOF with permanent porosity functions as a host for encapsulation of an enantiopure organic amine catalyst by combining carboxylic acids and chiral amines in situ through acid–base interactions. The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organocatalyst.
TL;DR: This review points at bio‐alternatives: currently known enzyme classes and organisms that catalyze the reduction of carboxylic acids are summarized.
Abstract: An increasing demand for non-petroleum-based products is envisaged in the near future. Carboxylic acids such as citric acid, succinic acid, fatty acids, and many others are available in abundance from renewable resources and they could serve as economic precursors for bio-based products such as polymers, aldehyde building blocks, and alcohols. However, we are confronted with the problem that carboxylic acid reduction requires a high level of energy for activation due to the carboxylate's thermodynamic stability. Catalytic processes are scarce and often their chemoselectivity is insufficient. This review points at bio-alternatives: currently known enzyme classes and organisms that catalyze the reduction of carboxylic acids are summarized. Two totally distinct biocatalyst lines have evolved to catalyze the same reaction: aldehyde oxidoreductases from anaerobic bacteria and archea, and carboxylate reductases from aerobic sources such as bacteria, fungi, and plants. The majority of these enzymes remain to be identified and isolated from their natural background in order to evaluate their potential as industrial biocatalysts.
TL;DR: In this paper, a nitrogen-functionalized active carbon-supported ultrasmall Pd nanoparticles were conveniently prepared by using a postloading method, and the Pd catalyst was highly active and selective for the hydrogenation of nitroarenes at room temperature under ambient pressure.
Abstract: Nitrogen-functionalized active carbon-supported ultrasmall Pd nanoparticles were conveniently prepared by using a postloading method. The Pd catalyst was highly active and selective for the hydrogenation of nitroarenes at room temperature under ambient pressure. Reducible groups such as ketone, carboxylic acid, and ester were not hydrogenated, and the corresponding anilines were obtained quantitatively. The Pd catalyst demonstrated high stability and could be reused 10times without the loss of catalytic performance.
TL;DR: In this article, 4,4′-biphenyldicarboxylate (bpdc) sodium salts with different compositions were evaluated for the first time as anodes for Na-ion batteries, and their crystal structures and corresponding electrochemical performances were analyzed.
Abstract: Novel 4,4′-biphenyldicarboxylate (bpdc) sodium salts with different compositions were evaluated for the first time as anodes for Na-ion batteries, and their crystal structures and corresponding electrochemical performances were analyzed. The structure of the bpdc-sodium salts was modified using precipitation and solvothermal methods to afford three different crystal structures with different degrees of deprotonation of the carboxylic acid (COOH) groups and different coordination of the water molecule, as determined by single crystal X-ray diffraction. The extent of deprotonation in bpdc-sodium salts not only affects their electrochemical performance, but also affects the corresponding reaction mechanisms. The fully deprotonated bpdc-disodium salt exhibits a promising electrochemical performance with a reversible capacity of about 200 mA h g−1 at ca. 0.5 V vs. Na/Na+, stable cycle performance over 150 cycles, and an excellent rate performance of 100 mA h g−1 even at a 20 C rate, which are better than those of the partially deprotonated bpdc-sodium salt. The sodiation–desodiation of bpdc-sodium salts proceeds in a two-phase reaction, regardless of the degree of deprotonation. However, unlike the fully deprotonated bpdc-disodium salt, which shows a reversible phase transition during sodiation and desodiation, the partially deprotonated bpdc-sodium salt exhibits an irreversible phase transition during cycling.
TL;DR: In this paper, ZnO-NPs with two different particle sizes, particle shapes, specific surface areas, and functional groups (OH group and carboxylic acid) were prepared through two different synthesis methods.
TL;DR: The catalytic mechanism for oxidizing alcohols to carboxylate in basic aqueous solution by the bipyridine-based ruthenium complex 2 (BIPY-PNN)Ru(H)(Cl)(CO) is investigated by density functional theory (DFT) with the ωB97X-D functional to derive chemoselectivity for the formation of carboxylic acid rather than ester.
Abstract: The catalytic mechanism for oxidizing alcohols to carboxylate in basic aqueous solution by the bipyridine-based ruthenium complex 2 (BIPY-PNN)Ru(H)(Cl)(CO) (Nat. Chem. 2013, 5, 122) is investigated by density functional theory (DFT) with the ωB97X-D functional. Using water as the oxygen donor with liberation of dihydrogen represents a safe and clean process for such oxidations. Under NaOH, the active catalyst is 3 (BIPY-PNN)Ru(H)(CO). Four steps are involved: dehydrogenation of alcohol to aldehyde (Step 1); coupling of aldehyde and water to form the gem-diol (Step 2); dehydrogenation of gem-diol to carboxylic acid (Step 3); and deprotonation of carboxylic acid to carboxylate anion under base (Step 4). The dehydrogenations of alcohol (Step 1) and gem-diol (Step 3) prefer the double hydrogen transfer mechanism to the β-H elimination mechanism. The coupling of aldehyde and water (Step 2) proceeds through cleavage of water by catalyst 3 followed by concerted hydroxyl and hydrogen transfer to the aldehyde. The formation of the carboxylate anion occurs via direct deprotonation of the carboxylic acid under base (Step 4), while in the absence of base a stable carboxylic acid-addition complex 6 was formed. Added base was found to play important roles in the generation of catalyst 3 from both the stable carboxylic acid-addition complex 6 and its chloride precursor complex 2. The chemoselectivity for the formation of carboxylic acid rather than ester is ascribed to the favorable cleavage of water and the subsequent generation of the stable carboxylate anion that leads to carboxylic acid upon acidification.
TL;DR: In this paper, a combination of IR, UV, 1H NMR and elemental analysis was used to demonstrate that the hydrolysis products contain a mixture of amide, carboxylic acid, ammonium carboxylate and sodium carboxymethylate structures.
Abstract: Chemical modification can be used to tailor the properties of PIM-1, the prototypical polymer of intrinsic microporosity, which shows promise for applications such as membrane and adsorption processes for gas and liquid separations. Base-catalysed hydrolysis of PIM-1 has previously been assumed to yield only carboxylated products. In this work, hydrolysis was carried out at 120 °C with 20% NaOH and at 100 °C with 10% NaOH in a water–ethanol mixture, and a combination of IR, UV, 1H NMR and elemental analysis was used to demonstrate that the hydrolysis products contain a mixture of amide, carboxylic acid, ammonium carboxylate and sodium carboxylate structures. The amide-PIM-1 structure has not previously been reported. Even the most fully hydrolysed samples had a substantial proportion of amide, with most samples being >50% amide. On hydrolysis there was a decrease in the water contact angle (from 85° for PIM-1 to about 60° for the most fully hydrolysed samples) and a decrease in the BET surface area. The adsorption of dyes from aqueous solution was shown to depend on the composition of the polymer. Uptake of the cationic dye Safranin O increased dramatically with increasing percentage carboxylation, the most highly carboxylated sample showing 31 times the uptake of the parent polymer, whereas uptake of the anionic dye Orange II decreased with increasing percentage carboxylation.
TL;DR: This unprecedented catalytic hydroboration of various terminal and internal alkynes with pinacolborane exhibits a broad functional groups compatibility, giving the corresponding alkenyl diboronates and monobor onates in good to high yields with exclusive regio- and stereoselectivities.
TL;DR: This work proposes the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis and applies this principle in a general and highly enantioselective catalytic aziridine-opening reaction with carboxYlic acids as nucleophiles.
Abstract: Organocatalysis, catalysis using small organic molecules, has recently evolved into a general approach for asymmetric synthesis, complementing both metal catalysis and biocatalysis. Its success relies to a large extent upon the introduction of novel and generic activation modes. Remarkably though, while carboxylic acids have been used as catalyst directing groups in supramolecular transition-metal catalysis, a general and well-defined activation mode for this useful and abundant substance class is still lacking. Herein we propose the heterodimeric association of carboxylic acids with chiral phosphoric acid catalysts as a new activation principle for organocatalysis. This self-assembly increases both the acidity of the phosphoric acid catalyst and the reactivity of the carboxylic acid. To illustrate this principle, we apply our concept in a general and highly enantioselective catalytic aziridine-opening reaction with carboxylic acids as nucleophiles.
TL;DR: A ruthenium(II) complex derived from the electron-deficient aromatic carboxylic acid 3-(F3C)C6H4CO2H proved to be a highly efficient catalyst for dehydrative alkyne annulation by NH-free hydroxamic acids in water.
Abstract: A ruthenium(II) complex derived from the electron-deficient aromatic carboxylic acid 3-(F3C)C6H4CO2H proved to be a highly efficient catalyst for dehydrative alkyne annulation by NH-free hydroxamic acids in water. The C–H/N–OH functionalization occurred with excellent positional selectivity as well as ample substrate scope, setting the stage for effective intermolecular alkenylations of hydroxamic acids. Detailed mechanistic studies were suggestive of a kinetically relevant C–H metalation by carboxylate assistance along with subsequent migratory alkyne insertion, reductive elimination, and intramolecular oxidative addition.
TL;DR: A radiotracer technique is utilized to track the exchange of a radiolabeled (14)C-oleic acid ligand with hydrophilic ligands on the surface of magnetite nanoparticles and shows that these ligand exchange reactions do not necessarily occur to completion as is often assumed, thus leaving a residual amount of oleic acid on thesurface of the particles.
Abstract: Ligand exchange of hydrophilic molecules on the surface of hydrophobic iron oxide nanoparticles produced via thermal decomposition of chelated iron precursors is a common method for producing aqueous suspensions of particles for biomedical applications. Despite the wide use, relatively little is understood about the efficiency of ligand exchange on the surface of iron oxide nanoparticles and how much of the hydrophobic ligand is removed. To address this issue, we utilized a radiotracer technique to track the exchange of a radiolabeled (14)C-oleic acid ligand with hydrophilic ligands on the surface of magnetite nanoparticles. Iron oxide nanoparticles functionalized with (14)C-oleic acid were modified with poly(ethylene glycol) with terminal functional groups including, L-3,4-dihydroxyphenylalanine, a nitrated L-3,4-dihydroxyphenylalanine, carboxylic acid, a phosphonate, and an amine. Following ligand exchange, the nanoparticles and byproducts were analyzed using liquid scintillation counting and inductively coupled plasma mass spectroscopy. The labeled and unlabeled particles were further characterized by transmission electron microscopy and dynamic light scattering to determine particle size, hydrodynamic diameter, and zeta potential. The unlabeled particles were characterized via thermogravimetric analysis and vibrating sample magnetometry. Radioanalytical determination of the (14)C from (14)C-oleic acid was used to calculate the amount of oleic acid remaining on the surface of the particles after purification and ligand exchange. There was a significant loss of oleic acid on the surface of the particles after ligand exchange with amounts varying for the different functional binding groups on the poly(ethylene glycol). Nonetheless, all samples demonstrated some residual oleic acid associated with the particles. Quantification of the oleic acid remaining after ligand exchange reveals a binding hierarchy in which catechol derived anchor groups displace oleic acid on the surface of the nanoparticles better than the phosphonate, followed by the amine and carboxylic acid groups. Furthermore, the results show that these ligand exchange reactions do not necessarily occur to completion as is often assumed, thus leaving a residual amount of oleic acid on the surface of the particles. A thorough analysis of ligand exchange is required to develop nanoparticles that are suitable for their desired application.