Showing papers on "Decarboxylation published in 2010"

Hydrazine and Thermal Reduction of Graphene Oxide: Reaction Mechanisms, Product Structures, and Reaction Design

Abstract: The density functional theory method (M05-2X/6-31G(d)) was used to investigate reaction mechanisms for deoxygenation of graphene oxides (GOs) with hydrazine or heat treatment. Three mechanisms were identified as reducing epoxide groups of GO with hydrazine as a reducing agent. No reaction path was found for the hydrazine-mediated reductions of the hydroxyl, carbonyl, and carboxyl groups of GO. We instead discovered the mechanisms for dehydroxylation, decarbonylation, and decarboxylation using heat treatment. The hydrazine de-epoxidation and thermal dehydroxylation of GO have opposite dependencies on the reaction temperature. In both reduction types, the oxygen functionalities attached to the interior of an aromatic domain in GO are removed more easily, both kinetically and thermodynamically, than those attached at the edges of an aromatic domain. The hydrazine-mediated reductions of epoxide groups at the edges are suspended by forming hydrazino alcohols. We provide atomic-level elucidation for the deoxyge...

Handbook of Biochemistry and Molecular Biology

Abstract: Amino Acids, Peptides and Proteins Properties of Amino Acids Data on the Naturally Occurring Amino Acids Structures and Symbols for Synthetic Amino Acids Incorporated Into Synthetic Polypeptides Unnatural Amino Acids for Incorporation into Proteins Properties of the alpha-Keto Acid Analogs of Amino Acids alpha,ss-Unsaturated Amino Acids Amino Acid Antagonists Coefficients of Solubility Equations of Certain Amino Acids in Water Heat Capacities, Absolute Entropies, and Entropies of Formation of Amino Acids and Related Compounds Heat of Combustion, Enthalpy and Free Energy of Formation of Amino Acids and Related Compounds Solubilities of Amino Acids in Water at Various Temperatures Heats of Solution of Amino Acids in Aqueous Solution at 25 C Free Energies of Solution and Standard Free Energy of Formation of Amino Acids in Aqueous Solution at 25 C Far Ultraviolet Absorption Spectra of Amino Acids UV Absorption Characteristics of N-Acetyl Methyl Esters of the Aromatic Amino Acids, Cystine and of N-Acetylcysteine Numerical Values of the Absorbances of the Aromatic Amino Acids in Acid, Neutral and Alkaline Solutions Luminescence of the Aromatic Amino Acids Luminescence of Derivatives of the Aromatic Amino Acids Luminescence of Proteins Lacking Tryptophan Luminescence of Proteins Containing Tryptophan Hydrophobicities of Amino Acids and Proteins Chemical Specificity of Reagents for Protein Modification Reagents for the Chemical Modification of Proteins Protein pK Values Protease Inhibitors and Protease Inhibitor Cocktails Assay of Solution Protein Concentration Spectrophotometric Determination of Protein Concentration in the Short-Wavelength Ultraviolet Lipids A Comprehensive Classification System for Lipids Properties of Fatty Acids and Their Methyl Esters Densities, Specific Volumes, and Temperature Coefficients of Fatty Acids from C8 to C12 Composition and Properties of Common Oils and Fats Androgens Bile Acids Corticoids Estrogens Progestogens Sterols Prostaglandins and Related Fatty-Acid Derived Materials Vitamins and Coenzymes Properties of Vitamins Biological Characteristics of Vitamins Properties for Ascorbic Acid and Ascorbate-2-Sulfate Vitamers Vitamin Names Discarded Nucleic Acids UV Spectral Characteristics and Acidic Dissociation Constants of 280 Alkyl Bases, Nucleosides, and Nucleotides Ultraviolet Absorbance of Oligonucleotides Containing 2'-O-Methylpentose Residues Spectrophotometric Constants of Ribonucleotides Purines, Pyrimidines, Nucleosides, and Nucleotides: Physical Constants and Spectral Properties Chemical Modification of Nucleic Acids Transfection Technologies Carbohydrates Introduction to Carbohydrates Natural Alditols, Inositols, Inososes, and Amino Alditols and Inosamines Natural Acids of Carbohydrate Derivation Natural Aldoses Natural Ketoses Carbohydrate Phosphate Esters The Naturally Occurring Amino Sugars Oligosaccharides (Including Disaccharides) Mucopolysaccharides (Glycosaminoglycans) Physical and Chemical Data Recommendations for Nomenclature and Tables in Biochemical Thermodynamics Standard Transformed Gibbs Energies of Formation for Biochemical Reactants Enthalpy, Entropy, and Free Energy Values for Biochemical Redox Reactions Oxidation-Reduction Potentials, Absorbance Bands and Molar Absorbance of Compounds used in Biochemical Studies Calorimetric DELTAH Values Accompanying Conformational Changes of Macromolecules in Solution Free Energies of Hydrolysis and Decarboxylation Deci-Normal Solutions of Oxidation and Reduction Reagents Guidelines for Potentiometric Measurements in Suspensions Part A. The Suspension Effect Ionization Constants of Acids and Bases Guidelines for NMR Measurements for Determination of High and Low pKa Values Measurement and Interpretation of Electrokinetic Phenomena Measurement of pH Definition, Standards, and Procedures General Comments on Buffers List of Buffers Bronsted Acidities Measurement of pH Buffer Solutions Amine Buffers Useful for Biological Research Preparation of Buffers for Use in Enzyme Studies Buffer for Acrylamide Gels (Single-Gel Systems) Starch Gels Indicators for Volumetric Work and pH Determinations Acid and Base Indicators Specific Gravity of Liquids Viscosity and Density Tables A Listing of Log P Values, Water Solubility, and Molecular Weight for Some Selected Chemicals Chemicals Commonly Used in Biochemistry and Molecular Biology and Their Properties Common Detergents Used in Biochemical Research Some Properties of Detergents and Surfactants Used in Biochemistry and Molecular Biology Some Biological Stains and Dyes Mordant Dyes Metal Chelating Agents Water Stability of Solutions for GLP and cGMP Use General Information on Spectroscopy Microplates Plastics Chemical and Physical Properties of Various Commercial Plastics Generic Source-Based Nomenclature for Polymers Definitions of Terms Relating to Reactions of Polymers and to Functional Polymeric Materials Definitions of Terms Related to Polymer Blends, Composites, and Multiphase Polymeric Materials Organic Name Reactions Useful in Biochemistry and Molecular Biology Enzymes in Synthetic Organic Chemistry Therapeutic Enzymes Weights of Cells and Cell Constituents Particle Diameter Appendix A: Abbreviations and Acronyms Appendix B: Glossary of Terms Useful in Biochemistry Index

Transition-Metal-CatalyzedRegioselective Arylation and Vinylation of CarboxylicAcids

Abstract: Arene and heteroarene carboxylic acids undergo regioselectivearylation and vinylation reactions at the positions ORTHO ( CINE)and IPSO to their carboxyl function undertransition-metal catalysis; these reactions are accompanied by carbon-hydrogenand carbon-carbon bond cleavages, respectively Recentprogress in this area is summarized in this article 1 Introduction 2 ORTHO- ( CINE-)Arylation 3 ORTHO- ( CINE-)Vinylation 4 IPSO-Arylation 5 IPSO-Vinylation 6 Conclusions

Room Temperature Palladium-Catalyzed Decarboxylative ortho-Acylation of Acetanilides with α-Oxocarboxylic Acids

Abstract: A novel Pd-catalyzed decarboxylative ortho-acylation of acetanilides with α-oxocarboxylic acids is realized at room temperature. This reaction provides efficient access to o-acyl acetanilides under mild conditions.

Catalytic reaction pathways in liquid-phase deoxygenation of C18 free fatty acids

Abstract: The liquid-phase deoxygenation of stearic, oleic, and linoleic acids employing a 5 wt% Pd/C catalyst was investigated using on-line quadrupole mass spectrometry (QMS). Catalytic deoxygenation of stearic acid (SA) under He occurs primarily via decarboxylation; the liquid products are n-heptadecane and heptadecenes. On-line QMS revealed concomitant CO2 and H2 evolution which can explain the greater than expected heptadecene yields at low to intermediate conversions. After essentially complete SA conversion, hydrogenation of heptadecenes via hydrogen transfer from the dodecane solvent results in 98% n-heptadecane yield. The initial rate of SA decarboxylation under 10% H2 is lower than under He; however, by avoiding the formation of unsaturated products the reaction requires much less time to reach completion. The SA decarboxylation rate under 10% H2 is 6-fold slower in heptadecane than in dodecane. This apparent solvent effect is explained by the lower vapor pressure of heptadecane resulting in greater H2 inhibition of the decarboxylation reaction. Our results demonstrate that the unsaturated C18 free fatty acids, oleic and linoleic, must be hydrogenated to SA before decarboxylation can proceed at a significant rate. Oleic acid (OA) deoxygenation under He occurs very slowly and primarily via decarbonylation. In contrast, OA deoxygenation under 10% H2 occurs facilely via hydrogenation to SA followed by decarboxylation. Since hydrogenation is complete during heating to reaction temperature, the decarboxylation kinetics and product yields are not affected by the initial unsaturation of the reactant.

Palladium-catalyzed decarboxylative couplings of 2-(2-azaaryl)acetates with aryl halides and triflates.

Abstract: Pd-catalyzed decarboxylative cross-couplings of 2-(2-azaaryl)acetates with aryl halides and triflates have been discovered. This reaction is potentially useful for the synthesis of some functionalized pyridines, quinolines, pyrazines, benzoxazoles, and benzothiazoles. Theoretical analysis shows that the nitrogen atom at the 2-position of the heteroaromatics directly coordinates to Pd(II) in the decarboxylation transition state.

Theoretical Analysis of Factors Controlling Pd-Catalyzed Decarboxylative Coupling of Carboxylic Acids with Olefins

Abstract: Transition-metal-catalyzed decarboxylative coupling presents a new and important direction in synthetic chemistry. Mechanistic studies on decarboxylative coupling not only improve the understanding of the newly discovered transformations, but also may have valuable implications for the development of more effective catalyst systems. In this work, a comprehensive theoretical study was conducted on the mechanism of Myers’ Pd-catalyzed decarboxylative Heck reaction. The catalytic cycle was found to comprise four steps: decarboxylation, olefin insertion, β-hydride elimination, and catalyst regeneration. Decarboxylation was the rate-limiting step, and it proceeded through a dissociative pathway in which Pd(II) mediated the extrusion of CO2 from an aromatic carboxylic acid to form a Pd(II)−aryl intermediate. Further analysis was conducted on the factors that might control the efficiency of Myers’ decarboxylative Heck reaction. These factors included Pd salts, ligands, acid substrates, and metals. (1) Regarding ...

Synthesis of Symmetrical and Unsymmetrical Diarylalkynes from Propiolic Acid Using Palladium-Catalyzed Decarboxylative Coupling

Abstract: Symmetrical diarylalkynes were obtained from propiolic acid (or 2-butynedioic acid) and aryl halides in good yields. The optimized reaction conditions were 2.0 equiv of aryl halide, 1.0 equiv of propiolic acid, 5.0 mol % Pd(PPh3)2Cl2, 10.0 mol % 1,4-bis(diphenylphosphino)butane (dppb), 2.0 equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and dimethyl sulfoxide (DMSO) as the solvent. The coupling reaction of 2-butynedioic acid with aryl halides required 110 °C. The coupling reaction showed tolerance for functional groups such as ester, ketone, and aldehyde and exhibited chemoselectivity. In the coupling reaction of propiolic acid with aryl bromide, the diarylated product was the major one at 80 °C, even though 1 equiv of aryl halides was employed. However, among the monoarylated products that were formed predominantly at 25 and 50 °C in the coupling reaction with aryl iodide, more Sonogashira coupling product was obtained than the decarboxylative coupling product. Unsymmetrical diarylalkynes were also sy...

γ-Valerolactone ring-opening and decarboxylation over SiO2/Al2O3 in the presence of water.

Abstract: γ-Valerolactone (GVL) has been identified as a promising, sustainable platform molecule that can be produced from lignocellulosic biomass. The chemical flexibility of GVL has allowed the development of a variety of processes to prepare renewable fuels and chemicals. In the present work involving a combination of computational and experimental studies, we explore the factors governing the ring-opening of GVL to produce pentenoic acid isomers, as well as their subsequent decarboxylation over acid catalysts or hydrogenation over metal catalysts. The ring-opening of GVL has shown to be a reversible reaction, while both the decarboxylation and hydrogenation reactions are irreversible and kinetically controlled under the conditions studied (temperatures from about 500 to 650 K). The most significant contributor to lactone reactivity toward ring-opening is the size of the ring, with γ- lactones being more stable and less readily opened than δ- and e-analogues. We have observed that the presence of either a C═C d...

A Versatile Catalyst for Intermolecular Direct Arylation of Indoles with Benzoic Acids as Arylating Reagents

Abstract: A novel catalyst system consisting of palladium trifluoroacetate, silver nitrate and propionic acid efficiently catalyzes the regioselective arylation of N-acyl indole derivatives (I) and (VII) with benzoic acids.

Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Benzyl Halides or Aryl Halides

Abstract: The synthesis of internal benzyl alkynes and 1,2-diarylalkynes has been developed via palladium-catalyzed decarboxylative coupling reactions of alkynyl carboxylic acids with benzyl chlorides or aryl halides. In the presence of Pd(OAc)2 and Xphos (L3), alkynyl carboxylic acids smoothly underwent the reaction with various benzyl halides, providing the corresponding benzyl alkynes in moderate to good yields. It is noteworthy that the optimal conditions are compatible with a wide range of aryl halides including less active aryl chlorides.

Comparative Study of Copper‐ and Silver‐Catalyzed Protodecarboxylations of Carboxylic Acids

Abstract: The protodecarboxylation of aromatic carboxylic acids by various copper and silver catalysts is investigated with the help of density functional calculations and experimental studies. The computational results reveal that the catalytic activity of copper(I)–1,10-phenanthroline catalysts increases with the introduction of electron-rich substituents at the phenanthroline ligand. They also predicted that for some substrates, silver complexes should possess a substantially higher decarboxylating activity than copper, which is confirmed by experimental studies, leading to the discovery of a silver(I) catalyst that effectively promotes the protodecarboxylation of various carboxylic acids at temperatures in the range of 80–120 °C—more than 50 °C below those of the best known copper(I) catalyst. The scope of the new system complements that of the copper(I)-based method as it includes benzoates for example, with halogen or ether groups in the ortho positions.

Palladium-catalyzed decarboxylative cross-coupling reaction between heteroaromatic carboxylic acids and aryl halides.

Abstract: A full overview of the decarboxylative cross-coupling reaction between heteroaromatic carboxylic acids and aryl halides is described This transformation employs palladium catalysts with short reaction times providing facile synthesis of aryl-substituted heteroaromatics The effect of each reaction parameter including solvent, base, and additive employed as well as the full substrate scope of this transformation are reported Mechanistic evidence is also disclosed that sheds light on possible reaction pathways

Enantioselective Synthesis of Spirocyclic Oxindole-β-lactones via N-Heterocyclic Carbene-Catalyzed Cycloaddition of Ketenes and Isatins

Abstract: Chiral N-heterocyclic carbenes were found to be efficient catalysts for the formal [2+2] cycloaddition reaction of disubstituted ketenes and isatins to give the corresponding spirocyclic oxindole-β-lactones in good yields with good diastereo-selectivities and excellent enantioselectivities. Ring opening with Grignard reagents or decarboxylation of the oxindole spirocyclic-β-lactone gave the corresponding 3-hydroxy- or 3-alkylenyloxindoles in good yields.

Fed-Batch Catalytic Deoxygenation of Free Fatty Acids

Abstract: Fed-batch catalytic deoxygenation of C18 free fatty acids (FFAs) to n-heptadecane was demonstrated in a 50 mL stirred autoclave reactor with continuous FFA injection via a high-pressure syringe pump. High selectivity to the hydrogen-neutral decarboxylation pathway was achieved using a 5 wt % Pd/C catalyst at 300 °C under 5% H2 (15 atm total pressure); the maximum quasi-steady-state deoxygenation rate under these conditions was 0.46 mmol gcat−1 min−1 [0.083 s−1 turnover frequency (TOF)] with 95% CO2 selectivity. In a separate experiment, quasi-steady-state SA deoxygenation activity was maintained for >24 h at 0.29 mmol gcat−1 min−1 (0.053 s−1 TOF) with 92% CO2 selectivity. When higher H2 partial pressures were employed, an abrupt switchover in reaction pathway and product selectivity from decarboxylation (CO2) to decarbonylation (CO) was observed. Higher CO selectivity leads to increased H2 consumption because of hydrogenation of heptadecenes, the primary products of the decarbonylation pathway. We infer t...

Aldehyde- and Ketone-Induced Tandem Decarboxylation-Coupling (Csp3−Csp) of Natural α-Amino Acids and Alkynes

Abstract: An interesting aldehyde- and ketone-induced intermolecular tandem decarboxylation-coupling (Csp3−Csp) catalyzed by copper with use of natural α-amino acids as starting materials is developed under neutral conditions with the production of CO2 and H2O as the only byproducts. Various functionalized nitrogen-containing compounds were obtained by this method. In these processes, interesting regioselectivites of the alkylation were observed, which has been rationalized by the relative stability of proposed resonance structures based on computation methods.

Boronic acid catalysis for mild and selective [3+2] dipolar cycloadditions to unsaturated carboxylic acids.

Abstract: Herein, the concept of boronic acid catalysis (BAC) for the activation of unsaturated carboxylic acids is applied in several classic dipolar [3+2] cycloadditions involving azides, nitrile oxides, and nitrones as partners. These cycloadditions can be used to produce pharmaceutically interesting, small heterocyclic products, such as triazoles, isoxazoles, and isoxazolidines. These cycloadducts are formed directly and include a free carboxylic acid functionality that can be employed for further transformations, thereby avoiding prior masking or functionalization. In all cases, BAC provides faster reactions, under milder conditions, with much improved product yields and regioselectivities. In some instances, such as triazole formation from the reaction of azides with 2-alkynoic acids, catalysis with ortho-nitrophenylboronic acid circumvents the undesirable product decarboxylation observed when using thermal activation. By using NMR spectroscopic studies, the boronic acid catalyst was shown to provide activation by a LUMO-lowering effect in the unsaturated carboxylic acid, likely via a monoacylated hemiboronic ester intermediate.

Three Coordination Polymers Based on 1H-Tetrazole (HTz) Generated via in Situ Decarboxylation: Synthesis, Structures, and Selective Gas Adsorption Properties

Abstract: Three tetrazole-based coordination polymers, [Zn3(Tz)6(H2O)2]n (1), [Cu2(Tz)3(OH)]n (2), and {[Cu5(Tz)9](NO3)·8H2O}n (3) (Tz = tetrazolate) have been prepared under hydro(solvo)thermal conditions using ethyl tetrazolate-5-carboxylate and corresponding metal salts as building blocks, in which tetrazolate was generated via in situ decarboxylation. The results of X-ray single diffraction analyses indicate that 1 possesses a 2D layer structure with μ2-Tz− bridged six- and four-coordinated Zn(II), forming a rare kagome dual topological layer. Compound 2 is a 3D layer−pillar structure, in which the Cu(II) ions are bridged by μ3-Tz− anions to generate a 2D sheet, and the 2D sheets are further pillared by μ2-Tz− and μ2-OH− to form a 3D framework with a fsc topology net. Compound 3 is a 3D porous framework with an acs topology net. Compound 1 exhibits photoluminescent properties with an emission peak at 467 nm, and compound 3 shows selective H2 and CO2 over N2 adsorption.