Showing papers on "Carboxylic acid published in 2016"

Nonclassical Routes for Amide Bond Formation

Abstract: The present review offers an overview of nonclassical (e.g., with no pre- or in situ activation of a carboxylic acid partner) approaches for the construction of amide bonds. The review aims to comprehensively discuss relevant work, which was mainly done in the field in the last 20 years. Organization of the data follows a subdivision according to substrate classes: catalytic direct formation of amides from carboxylic and amines (section 2); the use of carboxylic acid surrogates (section 3); and the use of amine surrogates (section 4). The ligation strategies (NCL, Staudinger, KAHA, KATs, etc.) that could involve both carboxylic acid and amine surrogates are treated separately in section 5.

Decarboxylative Cross-Electrophile Coupling of N-Hydroxyphthalimide Esters with Aryl Iodides.

Abstract: A new method for the decarboxylative coupling of alkyl N-hydroxyphthalimide esters (NHP esters) with aryl iodides is presented. In contrast to previous studies that form alkyl radicals from carboxylic acid derivatives, no photocatalyst, light, or arylmetal reagent is needed, only nickel and a reducing agent (Zn). Methyl, primary, and secondary alkyl groups can all be coupled in good yield (77% ave yield). One coupling with an acid chloride is also presented. Stoichiometric reactions of (dtbbpy)Ni(2-tolyl)I with an NHP ester show for the first time that arylnickel(II) complexes can directly react with NHP esters to form alkylated arenes.

Determination of corrosion inhibition effects of amino acids: Quantum chemical and molecular dynamic simulation study

Abstract: Amino acids are biologically important organic compounds in the human body which contain two important functional groups namely: –NH2 (amine) and –COOH (carboxylic acid) in their structures. In the present work, corrosion inhibitive performance amino acids such alanine (Ala), methionine (Met), aspartate (Asp), asparagine (Asn), lysine (Lys), arginine (Arg) and histidine (His) were investigated. All quantum chemical calculations related to these amino acids at the B3LYP/6-31G++(d, p) HF/6-31G++(d,p) methods were performed. Corrosion inhibition effects of the subject amino acids were discussed not only in the gas phase but also in the water phase, acetic acid and formic acid. Furthermore, molecular dynamic simulations employing Monte Carlo sampling approach were applied to search for the most stable configuration and adsorption energies for the interaction of the amino acid corrosion inhibitors on Cu (111)/50 H2O interface. A good correlation between theoretical data and experimental data has been obtained. Moreover, arginine that is a basic amino acid the best corrosion inhibitor among amino acids, considered in this study.

Silver-catalyzed carboxylation.

Abstract: Silver-catalyzed reactions are some of the important methodologies in organic chemistry. Since 2007, a new application of silver catalysts has been emerging. For the sequential carboxylation and cyclization of alkyne derivatives, such as propargyl alcohols and amines, using carbon dioxide, silver catalysts show significant reactivity under mild conditions unlike other transition metals. These developments have received much attention for the effective utilization of carbon dioxide in organic chemistry to synthesize heterocyclic compounds. Related silver-catalyzed C–C bond forming reactions with carbon dioxide have also provided the synthetic methods of the corresponding carboxylic acid derivatives. In this review, the recent studies of the silver-catalyzed carboxylation reactions using carbon dioxide are described.

Structure Property Relationships of Carboxylic Acid Isosteres

Abstract: The replacement of a carboxylic acid with a surrogate structure, or (bio)-isostere, is a classical strategy in medicinal chemistry. The general underlying principle is that by maintaining the features of the carboxylic acid critical for biological activity, but appropriately modifying the physicochemical properties, improved analogs may result. In this context, a systematic assessment of the physicochemical properties of carboxylic acid isosteres would be desirable to enable more informed decisions of potential replacements to be used for analog design. Herein we report the structure-property relationships (SPR) of 35 phenylpropionic acid derivatives, in which the carboxylic acid moiety is replaced with a series of known isosteres. The data set generated provides an assessment of the relative impact on the physicochemical properties that these replacements may have compared to the carboxylic acid analog. As such, this study presents a framework for how to rationally apply isosteric replacements of the carboxylic acid functional group.

Concurrent Cellulose Hydrolysis and Esterification to Prepare a Surface-Modified Cellulose Nanocrystal Decorated with Carboxylic Acid Moieties

Abstract: Cellulose nanocrystals (CNCs) were modified with natural di- and tricarboxylic acids using two concurrent acid-catalyzed reactions including hydrolysis of amorphous cellulose segments and Fischer esterification, resulting in the introduction of free carboxylic acid functionality onto CNC surfaces. CNC esterification was characterized by Fourier transform infrared spectroscopy, 13C solid state magic-angle spinning (MAS), and conductometric titration experiments. Average degree of substitution values for malonate, malate, and citrate CNCs are 0.16, 0.22, and 0.18, respectively. Despite differences in organic acid pKa, optimal HCl cocatalyst concentrations were similar for malonic, malic, and citric acids. After isolation of modified CNCs, residual cellulose coproducts were identified that are similar to microcrystalline cellulose based on SEM and XRD analysis. As proof of concept, recycling experiments were carried to increase the yield of citrate CNCs. The byproduct was then recycled by subsequent citric a...

Quantifying Ligand Exchange Reactions at CdSe Nanocrystal Surfaces

Abstract: The exchange reactions of X-type ligands at the surface of CdSe nanocrystals have been quantified via 1H NMR, absorbance, and emission spectroscopies. 1H NMR was used to quantify displacement reactions of oleate-capped CdSe nanocrystals with carboxylic-acid-, phosphonic-acid-, and thiol-terminated ligands that incorporate terminal alkene functionalities. The alkenyl protons of the native oleate ligand and the vinylic protons of the exchange ligand provide spectroscopic handles to quantify both free and surface-bound forms of these ligands. Undec-10-enoic acid was found to undergo an exchange equilibrium with oleate (Keq = 0.83), whereas phosphonic-acid- and thiol-terminated ligands irreversibly displace native oleate ligands. Absorption and emission experiments indicate that the carboxylic acid exchanges occur solely between surface-bound ligands, whereas exchange reactions with phosphonic acids and thiols alter the surface metal atoms of the nanocrystals, presumably through the displacement of Cd(oleate)...

Reusable Green Aerogels from Cross-Linked Hairy Nanocrystalline Cellulose and Modified Chitosan for Dye Removal.

Abstract: A novel biopolymer-based aerogel was developed by freeze-drying a hydrogel, synthesized from cross-linking bifunctional hairy nanocrystalline cellulose and carboxymethylated chitosan through a Schiff base reaction. The nanocelluloses, bearing aldehyde and carboxylic acid groups, facilitated the cross-linking with chitosan through imine bond formation while providing negatively charged functional groups, and chitosan was modified to accommodate carboxylic acid. The potential of this bioaerogel in environmental remediation was examined in a model system comprising methylene blue, a cationic dye. Electrostatic complexation between acidic groups on the anionic aerogel with the dye resulted in time-dependent dye adsorption, with long-time equilibrium dye concentration fitting well to the Langmuir isotherm, yielding a maximum adsorption capacity of ∼785 mg g–1 and equilibrium constant K ∼ 0.0089 at room temperature. Dynamics of adsorption was modeled by numerically solving the unsteady-state diffusion–adsorptio...

Atmospheric photochemistry at a fatty acid-coated air-water interface.

Abstract: Although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over a monolayer of NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase, and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet-state NA molecules excited by direct absorption of actinic light at the water surface. Because fatty acids–covered interfaces are ubiquitous in the environment, such photochemical processing will have a substantial impact on local ozone and particle formation.

Decarbonylative Silylation of Esters by Combined Nickel and Copper Catalysis for the Synthesis of Arylsilanes and Heteroarylsilanes

Abstract: An efficient nickel/copper-catalyzed decarbonylative silylation reaction of carboxylic acid esters with silylboranes is described. This reaction provides access to structurally diverse silanes with high efficiency and excellent functional-group tolerance starting from readily available esters.

Atmospheric photochemistry at a fatty acid coated air/water interface

Abstract: Although fatty acids are believed to be photochemically inert in the actinic region, complex volatile organic compounds are produced during illumination of an air-water interface coated solely with a monolayer of carboxylic acid. When aqueous solutions containing nonanoic acid (NA) at bulk concentrations that give rise to just over a monolayer of NA coverage are illuminated with actinic radiation, saturated and unsaturated aldehydes are seen in the gas phase, and more highly oxygenated products appear in the aqueous phase. This chemistry is probably initiated by triplet-state NA molecules excited by direct absorption of actinic light at the water surface. Because fatty acids–covered interfaces are ubiquitous in the environment, such photochemical processing will have a substantial impact on local ozone and particle formation.

Optimized Reaction Conditions for Amide Bond Formation in DNA-Encoded Combinatorial Libraries

Abstract: DNA-encoded combinatorial libraries are increasingly being used as tools for the discovery of small organic binding molecules to proteins of biological or pharmaceutical interest. In the majority of cases, synthetic procedures for the formation of DNA-encoded combinatorial libraries incorporate at least one step of amide bond formation between amino-modified DNA and a carboxylic acid. We investigated reaction conditions and established a methodology by using 1-ethyl-3-(3-(dimethylamino)propyl)carbodiimide, 1-hydroxy-7-azabenzotriazole and N,N′-diisopropylethylamine (EDC/HOAt/DIPEA) in combination, which provided conversions greater than 75% for 423/543 (78%) of the carboxylic acids tested. These reaction conditions were efficient with a variety of primary and secondary amines, as well as with various types of amino-modified oligonucleotides. The reaction conditions, which also worked efficiently over a broad range of DNA concentrations and reaction scales, should facilitate the synthesis of novel DNA-enco...

Improved Second Generation Iron Pincer Complexes for Effective Ester Hydrogenation

Abstract: Hydrogenation of esters to alcohols with a well-defined iron iPr2PNP pincer complex has been recently reported by us and other groups. We now introduce a novel and sterically less hindered Et2PNP congener that provides superior catalytic activity in the hydrogenation of various carboxylic acid esters and lactones compared to the known complex. Successful hydrogenation proceeds under relatively mild conditions (60 °C) with lower catalyst loadings.

Enantioselective CuH-Catalyzed Reductive Coupling of Aryl Alkenes and Activated Carboxylic Acids

Abstract: A new method for the enantioselective reductive coupling of aryl alkenes with activated carboxylic acid derivatives via copper hydride catalysis is described. Dual catalytic cycles are proposed, with a relatively fast enantioselective hydroacylation cycle followed by a slower diastereoselective ketone reduction cycle. Symmetrical aryl carboxyclic anhydrides provide access to enantioenriched α-substituted ketones or alcohols with excellent stereoselectivity and functional group tolerance.

Catalytic Conversion of Alcohols into Carboxylic Acid Salts in Water: Scope, Recycling, and Mechanistic Insights

Abstract: The catalytic conversion of alcohols into carboxylic acid salts in water was performed in the presence of ruthenium complexes supported by aliphatic PNP pincer ligands preformed or formed in situ. High activity toward a wide substrate scope was achieved with turnover number values of up to 4000. The air-stable catalytic system can be recycled by using toluene as a catalyst-immobilizing phase; the activity is maintained after five consecutive runs. Finally, mechanistic studies allowed some fundamental aspects related to water activation to be unveiled and to the mechanism postulated.

Colloidal metal oxide nanocrystal catalysis by sustained chemically driven ligand displacement.

Abstract: Here the authors show that nanocrystals of hafnium oxide can be applied as stable catalytic materials using a dynamic ligand-exchange reaction mechanism. Surface chemistry is a key enabler for colloidal nanocrystal applications. In this respect, metal oxide nanocrystals (NCs) stand out from other NCs as carboxylic acid ligands adsorb on their surface by dissociation to carboxylates and protons1,2, the latter proving essential in electron transfer reactions3. Here, we show that this binding motif sets the stage for chemically driven ligand displacement where the binding of amines or alcohols to HfO2 NCs is promoted by the conversion of a bound carboxylic acid into a non-coordinating amide or ester. Furthermore, the sustained ligand displacement, following the addition of excess carboxylic acid, provides a catalytic pathway for ester formation, whereas the addition of esters leads to NC-catalysed transesterification. Because sustained, chemically driven ligand displacement leaves the NCs—including their surface composition—unchanged and preserves colloidal stability, metal oxide nanocrystals are thus turned into effective nanocatalysts that bypass the tradeoff between colloidal stability and catalytic activity.

The synthesis and absorption dynamics of a lignin-based hydrogel for remediation of cationic dye-contaminated effluent

Abstract: Lignosulfonate- g -acrylic acid (LS- g -AA) hydrogels that possess superabsorbent capacity were synthesized by grafting acrylic acid (AA) on the backbone of lignosulfonate (LS) in the presence of N , N ′-methylene- bis -acrylamide (MBA) as initiated by laccase/ t -BHP(tert-butyl hydroperoxide). Specifically, the carboxylic acid groups introduced by grafting acrylic acid, significantly enhanced the absorption capacity of LS- g -AA hydrogels. In this case, methylene blue (MB) was the representative dye substrate to study absorption dynamics. It was found that the equilibrium absorption of MB reached 2013 mg·g − 1 while pH, absorption time, and initial MB concentration affected the overall absorption capacity. The absorption isotherms and kinetics obeyed standard Freundlich and pseudo-2nd-order models, respectively. Furthermore, preliminary desorption experiments were conducted in weak acid solution and showed that ~ 50% of the original MB could be removed over one rinse cycle.

Multiple Roles of the Pyrimidyl Group in the Rhodium-Catalyzed Regioselective Synthesis and Functionalization of Indole-3-carboxylic Acid Esters

Abstract: A regioselective synthesis of indole-3-carboxylic acid esters from anilines and diazo compounds has been realized by making use of the pyrimidyl group-assisted rhodium-catalyzed CH activation and CN bond formation. The reaction proceeds under mild conditions, exhibits good functional group tolerance and scalability. Reutilization of the pyrimidyl directing group in the resulting products provided an efficient strategy for further C-7 functionalization of indoles. Moreover, the pyrimidyl moiety could be readily removed as a leaving group to offer various free NH indoles.

Direct Catalytic Chemoselective α-Amination of Acylpyrazoles: A Concise Route to Unnatural α-Amino Acid Derivatives

Abstract: A direct copper-catalyzed highly chemoselective α-amination is described. Acylpyrazole proved to be a highly efficient enolate precursor of a carboxylic acid oxidation state substrate, while preactivation by a stoichiometric amount of strong base has been used in catalytic α-aminations. The simultaneous activation of both coupling partners, enolization and metal nitrenoid formation, was crucial for obtaining the product, and wide functional group compatibility highlighted the mildness of the present catalysis. The bidentate coordination mode was amenable to highly chemoselective activation over ketone and much more acidic nitroalkyl functionality. Deuterium exchange experiments clearly demonstrated that exclusive enolization of acylpyrazole was achieved without the formation of a nitronate. The present catalysis was applied to late-stage α-amination, allowing for concise access to highly versatile α-amino acid derivatives. The product could be transformed into variety of useful building blocks.

pH-Driven Self-Assembly of Acidic Microbial Glycolipids

Abstract: Microbial glycolipids are a class of well-known compounds, but their self-assembly behavior is still not well understood. While the free carboxylic acid end group makes some of them interesting stimuli-responsive compounds, the sugar hydrophilic group and the nature of the fatty acid chain make the understanding of their self-assembly behavior in water not easy and highly unpredictable. Using cryo-transmission electron microscopy (cryo-TEM) and both pH-dependent in situ and ex situ small angle X-ray scattering (SAXS), we demonstrate that the aqueous self-assembly at room temperature (RT) of a family of β-d-glucose microbial glycolipids bearing a saturated and monounsaturated C18 fatty acid chain cannot be explained on the simple basis of the well-known packing parameter. Using the “pH-jump” process, we find that the molecules bearing a monosaturated fatty acid forms vesicles below pH 6.2, as expected, but the derivative with a saturated fatty acid forms infinite bilayer sheets below pH 7.8, instead of ves...

Nitrous Oxide as a Hydrogen Acceptor for the Dehydrogenative Coupling of Alcohols

Abstract: The oxidation of alcohols with N2O as the hydrogen acceptor was achieved with low catalyst loadings of a rhodium complex that features a cooperative bis(olefin)amido ligand under mild conditions. Two different methods enable the formation of either the corresponding carboxylic acid or the ester. N2 and water are the only by-products. Mechanistic studies supported by DFT calculations suggest that the oxygen atom of N2O is transferred to the metal center by insertion into the Rh−H bond of a rhodium amino hydride species, generating a rhodium hydroxy complex as a key intermediate.