Showing papers on "Carboxylic acid published in 2001"

Lipid Formation by Aqueous Fischer-Tropsch-Type Synthesis over a Temperature Range of 100 to 400 °C

Abstract: The formation of lipid compounds during anaqueous Fischer-Tropsch-type reaction was studied withsolutions of oxalic acid as the carbon and hydrogensource. The reactions were conducted in stainlesssteel vessels by heating the oxalic acid solution atdiscrete temperatures from 100 to 400 °C, atintervals of 50 °C for two days each. Themaximum lipid yield, especially for oxygenatedcompounds, is in the window of 150–250 °C. At atemperature of 100 °C only a trace amount oflipids was detected. At temperatures above150 °C the lipid components ranged from C12to >C33 and included n-alkanols, n-alkanoic acids, n-alkyl formates, n-alkanals, n-alkanones, n-alkanes, andn-alkenes, all with essentially no carbon numberpreference. The n-alkanes increased inconcentration over the oxygenated compounds attemperatures of 200 °C and above, with a slightreduction in their carbon number ranges due tocracking. It was also noted that the n-alkanoicacids increased while n-alkanols decreased withincreasing temperature above 200 °C. Attemperatures above 300 °C synthesis competeswith cracking and reforming reactions. At 400 °Csignificant cracking was observed and polynucleararomatic hydrocarbons and their alkylated homologswere detected. The results of this work suggest thatthe formation of lipid compounds by aqueous FTTreactions proceeds by insertion of a CO group at theterminal end of a carboxylic acid functionality toform n-oxoalkanoic acids, followed by reductionto n-alkanoic acids, to n-alkanals, thento n-alkanols. The n-alkenes areintermediate homologs for n-alkan-2-ones andn-alkanes. This proposed mechanism for aqueousFTT synthesis differs from the surface-catalyzedstepwise FT process (i.e., gaseous) of polymerization of methylene reported in the literature.

Studies on the Reversible Aggregation of Cysteine-Capped Colloidal Silver Particles Interconnected via Hydrogen Bonds

Abstract: The surface modification of aqueous silver colloidal particles with the amino acid cysteine and the cross-linking of the colloidal particles in solution is described. Capping of the silver particles with cysteine is accomplished by a thiolate bond between the amino acid and the nanoparticle surface. The silver colloidal particles are stabilized electrostatically by ionizing the carboxylic acid groups of cysteine. Aging of the cysteine-capped colloidal solution leads to aggregation of the particles via hydrogen bond formation between amino acid molecules located on neighboring silver particles. The aggregation is reversible upon heating the solution above 60 °C. The rate of cross-linking of the silver particles via hydrogen bond formation may be accelerated by screening the repulsive electrostatic interactions between the particles using salt. The process of aggregation and heat-induced dispersion of the particles has been studied by UV−vis spectroscopy, laser light scattering, and transmission electron mi...

Cadmium mobilisation and plant availability – the impact of organic acids commonly exuded from roots

Abstract: The present work highlights metal-organic acid interactions with special reference to their plant availability Pot experiments were conducted to investigate the effect of various organic (carboxylic and amino) acids on the uptake and translocation of root-absorbed Cd by maize (Zea mays) plants grown in sand and soil culture Statistically significant increases in Cd accumulation from Cd-treated plants in the presence of increasing concentrations of organic acids, suggest the existence of Cd-organic acid interactions in the soil-plant system In order to support the above hypothesis of formation of organically bound Cd, separate experiments were performed to synthesize and estimate its various forms viz cationic, anionic and neutral The chemical nature of the organically bound forms was ascertained by electrophoretic experiments Amino acids have been found to be less effective in the mobilisation of cadmium compared to carboxylic acids The results are discussed on the basis of the potential of organic acids to form complexes with Cd

Gas-Phase OH Oxidation of Monoterpenes: Gaseous and Particulate Products

Abstract: Smog chamber experiments have beenconducted in which cyclic monoterpenes were oxidisedin the gas phase by OH The evolved secondary organicaerosol (SOA) was analysed by LC-MSn and thegas-phase products were analysed by FT-IR Theconcentrations of the identified compoundscorresponded to carbon mass balances in the range of40%–90% The identified compounds in the particularphase corresponded to 05%–42% of the reactedcarbon The most abundant compounds in SOA fromterpenes with an endocyclic C=C double bond wereC10-keto-aldehydes, C10-keto-carboxylicacids, C10-hydroxy-keto-carboxylic acids, andC10-hydroxy-keto-aldehydes (pinonaldehyde,pinonic acid, hydroxy-pinonic acid isomers, andhydroxy-pinonaldehyde isomers from α-pinene;3-caronaldehyde, 3-caronic acid, hydroxy-3-caronicacid isomers, and hydroxy-3-caronaldehyde isomers from3-carene) The most abundant compounds in SOA fromterpenes with an exocyclic C=C double bond wereC9-ketones, C9-dicarboxylic acids, andC10-hydroxy-keto-carboxylic acids (nopinone,pinic acid, and hydroxy-pinonic acid isomers fromβ-pinene; sabinaketone, sabinic acid andhydroxy-sabinonic acid isomers from sabinene)Decarboxylated analogues of most of the compounds werepresent in SOA in minor concentrations, such asC9-keto-carboxylic acids (norpinonic acid,nor-3-caronic acid) and C8-dicarboxylic acids(norpinic acid, nor-3-caric acid, norsabinic acid) InSOA from limonene, which contains an endocyclic aswell as an exocyclic C=C double bond, the mostabundant compounds were a C10-keto-aldehyde andits oxo-derivative (limononaldehyde and keto-limononaldehyde) together with hydroxy-derivatives of aC10-keto-carboxylic acid (isomers ofhydroxy-limononic acid) Also aC10-keto-carboxylic acid (limononic acid) waspresent together with minor concentrations of aC9-dicarboxylic acids (limonic acid), itsoxo-derivative (keto-limonic acid), and itsdecarboxylated analogue (norlimonic acid) Mechanisticpathways for the formation of these products, some ofwhich are identified here for the first time, areproposed

Molecular Resolution and Fragmentation of Fulvic Acid by Electrospray Ionization/Multistage Tandem Mass Spectrometry

Abstract: Molecular weight distributions of fulvic acid from the Suwannee River, Georgia, were investigated by electrospray ionization/quadrupole mass spectrometry (ESI/ QMS), and fragmentation pathways of specific fulvic acid masses were investigated by electrospray ionization/ion trap multistage tandem mass spectrometry (ESI/MST/ MS). ESI/QMS studies of the free acid form of low molecular weight poly(carboxylic acid) standards in 75% methanol/25% water mobile phase found that negative ion detection gave the optimum generation of parent ions that can be used for molecular weight determinations. However, experiments with poly(acrylic acid) mixtures and specific high molecular weight standards found multiply charged negative ions that gave a low bias to molecular mass distributions. The number of negative charges on a molecule is dependent on the distance between charges. ESI/MST/MS of model compounds found characteristic water loss from alcohol dehydration and anhydride formation, as well as CO 2 loss from decarboxylation, and CO loss from ester structures. Application of these fragmentation pathways to specific masses of fulvic acid isolated and fragmented by ESI/MST/MS is indicative of specific structures that can serve as a basis for future structural confirmation after these hypothesized structures are synthesized.

Interpreting Infrared, Raman, and Nuclear Magnetic Resonance Spectra

Abstract: Volume 1: Theory of Vibrational Spectroscopy Experimental Alkyl Carbon-Hydrogen Vibrations Alkenes and Other Compounds Containing C=C Double Bonds Alkynes and Compounds Containing C=C Groups Carboxamides, Ureas, Thioureas, Imidazolidinones, Caffeine, Isocaffeine, Uracils, Imides, Hydantoins, and s-Triazine (1H, 3H, 5H)- Triones Aldehydes Ketones Carboxylic Acid Esters Organic Carbonates, Thiol Carbonates, Chloroformates, Thiol Chloroformates, Acetyl Chloride, Benzoyl Chloride, Carbamates, and an Overview of Solute-Solvent Effects Upon Carbonyl Stretching Frequencies Volume 2: Epoxides and Ethers Nitriles, Isonitriles, and Dialkyl Cyanamides Azines, Isocyanates, Isothiocyanates, and Carbodiimides Thiols, Sulfides and Disulfides, Alkanethiols, and Alkanedithiols (S--H stretching) Sulfoxides, Sulfones, Sulfates, Monothiosulfates, Sulfonyl Halides, Sulfites, Sulfonamides, Sulfonates, and N-Sulfinyl Anilines Halogenated Hydrocarbons Nitroalkanes, Nitrobenzenes, Alkyl Nitrates, Alkyl Nitrites, and Nitrosamines Phosphorus Compounds Benzene and Its Derivatives The Nyquist Vibrational Group Frequency Rule Infrared Raman and Nuclear Magnetic Resonance (NMR) Spectra-Structure Correlations for Organic Compounds

Oxidations by the reagent “O2–H2O2–vanadium derivative–pyrazine-2-carboxylic acid”. Part 12.1 Main features, kinetics and mechanism of alkane hydroperoxidation

Abstract: Various combinations of vanadium derivatives (n-Bu4NVO3 is the best catalyst) with pyrazine-2-carboxylic acid (PCA) catalyse the oxidation of saturated hydrocarbons, RH, with hydrogen peroxide and air in acetonitrile solution to produce, at temperatures <40 °C, alkyl hydroperoxides, ROOH, as the main primary products. These compounds are easily reduced with triphenylphosphine to the corresponding alcohols, which can then be quantitatively determined by GLC. Certain aminoacids similar to PCA can play the role of co-catalyst; however the oxidation rates and final product yields are lower for picolinic and imidazole-4,5-dicarboxylic acids, while imidazole-4-carboxylic and pyrazole-3,5-dicarboxylic acids are almost inactive. The oxidation is induced by the attack of a hydroxyl radical on the alkane, RH, to produce alkyl radicals, R˙. The latter further react rapidly with molecular atmospheric oxygen. The peroxyl radicals, ROO˙, thus formed can be converted to alkyl hydroperoxides. We conclude on the basis of our kinetic investigation of the oxidation of cyclohexane that the rate-limiting step of the reaction is the monomolecular decomposition of the complex containing one coordinated PCA molecule: VV(PCA)(H2O2) → VIV(PCA) + HOO˙ + H+. The VIV species thus formed reacts further with a second H2O2 molecule to generate the hydroxyl radical according to the equation VIV(PCA) + H2O2 → VV(PCA) + HO˙ + HO−. The concentration of the active species in the course of the catalytic process has been estimated to be as low as [V(PCA)H2O2] ≊ 3.3 × 10−6 mol dm−3. The effective rate constant for the cyclohexane oxidation (d[ROOH]/dt = keff[H2O2]0[V]0) is keff = 0.44 dm3 mol−1 s−1 at 40 °C, the effective activation energy is 17 ± 2 kcal mol−1. It is assumed that the accelerating role of PCA is due to its facilitating the proton transfer between the oxo and hydroxy ligands of the vanadium complex on the one hand and molecules of hydrogen peroxide and water on the other hand. For example: (pca)(O)V⋯H2O2 → (pca)(HO–)V–OOH. Such a “robot’s arm mechanism” has analogies in enzyme catalysis.

Proton-Controlled Electron Injection from Molecular Excited States to the Empty States in Nanocrystalline TiO2

Abstract: The excited-state and redox properties of Ru(deeb)(bpy)2(PF6)2, Ru(dcb-H2)(bpy)2(PF6)2, Ru(bpy)2(ina)2(PF6)2, and Ru(dpbp)(bpy)2(PF6)2, where bpy is 2,2‘-bipyridine, deeb is 4,4‘-(CO2Et)2-bpy, dcb-H2 is 4,4‘-(CO2H)2-bpy, dpbp is 4,4‘-(PO(OEt)2)2-bpy, and ina is isonicotinic acid, bound to nanocrystalline TiO2 and colloidal ZrO2 films have been studied in acetonitrile at room temperature as a function of the interfacial proton concentration. High surface proton concentrations favor a “carboxylic acid” type linkage(s) where low proton concentrations favor “carboxylate” type binding mode(s) for Ru(II) compounds with ethyl ester or carboxylic acid functional groups. The “carboxylic acid” linkages are unstable when Lewis acids such as Li+ are present in acetonitrile, while desorption is absent for the carboxylate binding under the same conditions. The kinetics for binding are faster when the interfacial proton concentration is high; however, the saturation surface coverage is about 1/3 lower than for base-pret...

Enzymatic Routes to Enantiomerically Pure Aromatic α‐Hydroxy Carboxylic Acids: A Further Example for the Diversity of Biocatalysis

Abstract: An important class of compounds which can be produced by means of enzymatic routes are enantiomerically pure aromatic α-hydroxy carboxylic acids, in particular mandelic acid and derivatives thereof. Numerous different types of enantioselective biocatalytic approaches to these target molecules have been developed. Among them are chiral enzymatic resolution processes using racemic precursors as well as asymmetric catalytic methods starting from prochiral compounds. Regarding the resolution processes, nitrilase-catalyzed hydrolysis and dehydrocyanation of racemic cyanohydrins as well as stereocontrolled ester cleavage of O-acetylcyanohydrins and α-hydroxy carboxylic acid esters, respectively, have been developed. Main contributions in the field of asymmetric catalytic concepts are the asymmetric reduction of α-keto acids as well as the asymmetric hydrocyanation of aldehydes. In the latter case, a subsequent chemical hydrolysis gives the desired products. In the following, these different concepts for the biocatalytic preparation of aromatic α-hydroxy carboxylic acid are discussed showing that biocatalysis can provide the organic chemist with many versatile synthetic pathways to obtain chiral aromatic α-hydroxy carboxylic acids. 1 Introduction 2 Overview: Biocatalytic Routes to Aromatic α-Hydroxy Carboxylic Acids 3 Route A: Enzymatic Hydrolysis of an Ester Group 4 Route B: Biocatalytic Transesterification − Enzymatic Hydrolysis of the O-Acetyl Group 5 Route C: Enzymatic Hydrolysis of the Cyano Group 6 Route D: Enzymatic Cleavage of rac-Cyanohydrins 7 Route E: Enantioselective Biocatalytic Hydrocyanation of Aromatic Aldehydes 7.1 Enzymatic Enantioselective Hydrocyanation in Organic Media 7.2 Enzymatic Enantioselective Hydrocyanation in Aqueous Media 7.3 Enzymatic Enantioselective Hydrocyanation in Biphasic Solvent Systems 7.4 Chemical Hydrolysis of Enantiomerically Enriched Cyanohydrins 8 Route F: Enantioselective Reduction of α-Keto Acids and Esters Thereof 9 Summary and Outlook

Radical carboxylations of iodoalkanes and saturated alcohols using carbon monoxide

Abstract: This review covers two radical carboxylation methods using carbon monoxide, both of which were developed by our group. The first method, atom transfer carbonylation, converts alkyl iodides into carboxylic acid esters or amides and the second method, remote carboxylation, converts saturated alcohols into δ-lactones. Both methods rely upon radical carbonylation chemistry to introduce carbon monoxide, but the key steps are conceptually different. The first method utilizes an atom transfer reaction from an alkyl iodide to an acyl radical leading to an acyl iodide and the latter employs a one-electron oxidation reaction to convert an acyl radical into an acyl cation. The iodine atom transfer carbonylation process is reversible and therefore highly inefficient unless it is performed in concert with an ionic system to shift the equilibrium in the direction of an acyl iodide. In the latter process, a 1,5-translocation scheme to shift the radical from oxygen to the δ-carbon is successfully coupled with the carbonylation–oxidation sequence. Carboxylations of alkyl halides by transition metal catalyzed methods are often problematic because of the inherent weakness of alkyl–metal bonds. Existing methods for carbonylative δ-lactone synthesis using transition metal catalysts are limited to unsaturated alcohols. Thus, these two radical carboxylation methods nicely complement existing transition metal catalyzed carboxylations.

Single-step, highly active, and highly selective nanoparticle catalysts for the hydrogenation of key organic compounds

Abstract: Pores for cluster catalysts: Nanoparticles of both Ru5Pt and Ru10Pt2, uniformly distributed along the inner walls of mesoporous silica, exhibit high catalytic performance in the single-step hydrogenation of dimethyl terephthalate (DMT, to 1,4-cyclohexanedimethanol (CHDM); see scheme), of benzoic acid (to cyclohexane carboxylic acid), and of naphthalene (in the presence of sulfur) to cisdecalin.

Uracil moiety is required for toxicity of the cyanobacterial hepatotoxin cylindrospermopsin.

Abstract: A new natural derivative of the sulfated guanidinium zwitterionic toxin cylindrospermopsin, 7-epi-cylindrospermopsin, was recently isolated from the cyanobacterium Aphanizomenon ovalisporum (Forti). The toxicity of the molecule (LD50 ip 5 d), estimated by mouse bioassay, was 200 µg/kg mouse, a value similar to that of cylindrospermopsin. Treatment of cylindrospermopsin with chlorine solution or chlorine-related oxidants produced two new derivatives. The chemical structure of these products was elucidated by nuclear magnetic resonance (NMR) and mass spectrometry (MS) techniques and toxicity was determined. In the first derivative, the vinylic proton at position 5 of the pyrimidine ring was substituted by chlorine to yield 5-chlorocylindrospermopsin. The other product is a truncated one, where C-6 of the pyrimidine ring was oxidized to a carboxylic acid. A trivial name, cylindrospermic acid, was given to this compound. Both products showed no toxic effects even at doses 50 times higher than the LD50 of cyli...

Oxidations by the system “hydrogen peroxide–manganese(IV) complex–carboxylic acid”: Part 3. Oxygenation of ethane, higher alkanes, alcohols, olefins and sulfides

Abstract: The manganese(IV) complex salt [L2Mn2O3](PF6)2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) (compound 1, see Scheme 1) very efficiently catalyzes the hydroperoxidation of saturated hydrocarbons, including ethane by H2O2 in acetontitrile or nitromethane solution at low (room or lower) temperature, provided a carboxylic (typically acetic) acid is present. The hydroperoxidation of tertiary positions in disubstituted cyclohexanes proceeds with partial retention of configuration in nitromethane or acetonitrile solution, while the stereoselectivity of the reaction is only negligible in acetone solution. The system “H2O2–compound 1–MeCO2H” also transforms secondary alcohols into the corresponding ketones with quantitative yields at room temperature within a few minutes; the yields of aldehydes and carboxylic acids in the oxidation of primary alcohols are lower. Terminal aliphatic olefins such as hexene-1 are quantitatively epoxidized by the same system in acetonitrile at room temperature within 20 min, while the epoxide yield in the analogous reaction with styrene attains only 60% under the same conditions. Finally, dimethylsulfide can be quantitatively and selectively converted into dimethylsulfoxide within 3 h at room temperature. The system “tert-BuOOH–compound 1” also oxidizes alkanes, addition of acetic acids has less pronounced effect on the direction and efficiency of the reaction. Two other checked derivative of Mn(IV) (compounds 2 and 3) as well a porphyrin complex of Mn(III) (compound 4) exhibited lower activity in catalysis of alkane oxidation with tert-BuOOH. © 2001 Elsevier Science B.V. All rights reserved.

Characterization of Dicarboxylic Acids for Cellulose Hydrolysis

Abstract: In this paper, we show that dilute maleic acid, a dicarboxylic acid, hydrolyzes cellobiose, the repeat unit of cellulose, and the microcrystalline cellulose Avicel as effectively as dilute sulfuric acid but with minimal glucose degradation. Maleic acid, superior to other carboxylic acids reported in this paper, gives higher yields of glucose that is more easily fermented as a result of lower concentrations of degradation products. These results are especially significant because maleic acid, in the form of maleic anhydride, is widely available and produced in large quantities annually.

Liquid-Phase Esterification of Propionic Acid with n-Butanol

Abstract: Kinetic data on the esterification of propionic acid with n-butanol catalyzed by Amberlyst 15, Amberlyst 35, Amberlyst 39, and HZSM-5 pellets were measured at the temperatures from 353 to 383 K in ...

Evaporation Rates and Vapor Pressures of Individual Aerosol Species Formed in the Atmospheric Oxidation of α- and β-Pinene

Abstract: The semivolatile oxidation products (trans-norpinic acid, pinic acid, cis-pinonic acid, etc.) of the biogenic monoterpenes (α-pinene, β-pinene, etc.) contribute to the atmospheric burden of particulate matter. Using the tandem differential mobility analysis (TDMA) technique evaporation rates of glutaric acid, trans-norpinic acid, and pinic acid particles were measured in a laminar flow reactor. The vapor pressure of glutaric acid was found to be log(p0glutaric/Pa) = − 3510 K/T + 8.647 over the temperature range 290−300 K in good agreement with the values previously reported by Tao and McMurry (1989). The measured vapor pressure of trans-norpinic acid over the temperature range 290−312 K is log(p0norpinic/Pa) = − 2196.9 K/T + 3.522, and the vapor pressure of pinic acid is log(p0pinic/Pa) = − 5691.7 K/T + 14.73 over the temperature range 290−323 K. The uncertainty on the reported vapor pressures is estimated to be approximately ± 50%. The vapor pressure of cis-pinonic acid is estimated to be of the order of...

Influence of the COOH and COONa groups and crosslink density of poly(acrylic acid)/ montmorillonite superabsorbent composite on water absorbency

Abstract: A novel poly(acrylic acid)/montmorillonite superabsorbent composite with a water absorbency of 1100 times its own weight was synthesized by the graft copolymerization of acrylic acid with a cross-linking agent in the presence of montmorillonite ultrafine powder. The influence of the amount of crosslinker and montmorillonite on water absorbency has been investigated. It was found that a crosslinker concentration of 0.03 wt% and 30 wt% montmorillonite gave the best results. The collaborative absorbent effect of sodium carboxylate and carboxylic acid groups was superior to that of sodium carboxylate or carboxylic acid groups alone, and the composite with a ratio of about 2/3 for sodium carboxylate to carboxyl acid groups possessed the highest water absorbence. © 2001 Society of Chemical Industry

Hydrogenation of oleic acid over ruthenium catalysts

Abstract: The performance of ruthenium-tin catalysts for the liquid phase selective hydrogenation of oleic acid to unsaturated alcohols has been investigated. Titania-supported ruthenium and ruthenium-tin catalysts prepared by conventional impregnation as well as alumina-supported sol–gel ruthenium and ruthenium-tin catalysts have been used. The hydrogenation over the monometallic ruthenium catalysts leads primarily to the saturated stearic acid, which is then consecutively hydrogenated to the saturated stearyl alcohol. The titania-supported monometallic ruthenium catalyst shows a greater activity than the alumina-supported sol–gel one for the hydrogenation of oleic acid to the saturated stearyl alcohol. The hydrogenation over the bimetallic ruthenium-tin catalysts is characterized by the near total suppression of the hydrogenation of the olefine bond in favor of the activation of the hydrogenation of the carboxylic bond, thus leading to the selective formation of unsaturated alcohols. Besides, these catalysts are active for the cis–trans isomerization reaction of the oleic acid to elaidic acid, in competition with the hydrogenation of the carboxylic group. The impregnated titania-supported ruthenium-tin catalyst shows a better performance than the alumina-supported sol–gel ruthenium-tin catalyst for the selective hydrogenation of oleic acid to unsaturated alcohols.