Ruthenium catalysed oxidation without CCl4 of oleic acid, other monoenic fatty acids and alkenes

Ruthenium catalysed oxidation of alkenes and monoenic fatty acids is reported. The study of the influence of cosolvents (H₂O/MeCN/X) shows that toxic CCl₄ initially used in the Sharpless system (H₂O/MeCN/CCl₄) can be avoided and demonstrates that the oxidative cleavage of CC bond could be accomplished in good yields with H₂O/MeCN/AcOEt solvent system in a ratio 3/2/2, respectively.     

Protonation and deprotonation of hydroxamic acids. An MO ab initio study

Ab initio molecular orbital calculations with 4-31G//4-31G, 6-31G^*//4-31G and 6-31+G//4-31G basis sets have been used to examine the structure, relative energy, protonation and deprotonation of a series of seven hydroxamic acids in the gas phase. The results show that hydroxamic acids are predominantly in the E-TS form and that the most probable protonation site is the carbonyl oxygen atom, while deprotonation proceeds by loss of NH hydrogen.     

Selective preparation of terminal alkenes from aliphatic carboxylic acids by a palladium-catalysed decarbonylation-elimination reaction

Trialkylamines were used as additives in the decarbonylation-elimination reaction catalysed by the combination of palladium(II) chloride and DPE-Phos. Aliphatic carboxylic acids were transformed at relatively low temperature into terminal alkenes in high yield and high selectivity, without the need for distillation, thereby avoiding isomerisation.     

GC—MS analysis of carboxylic acids in petroleum after esterification with fluoroalcohols

The GC–MS characteristics of carboxylic acid esters prepared from fluorine-containing alcohols were compared to those of methyl esters. The GC retention of 2,2,2-trifluoroethyl (TFE) esters was less than, and 2,2,3,3,4,4,4-heptafluoro-1-butyl (HFB) esters was approximately equivalent to that of methyl esters. Mass spectra of TFE and HFB aliphatic esters show significantly more intense molecular and key fragment ions than those of methyl esters. Also, owing to their significantly higher molecular weights, TFE or HFB ester molecular ions and most fragment ions of interest occur at significantly higher m/z values than most potential interfering ions. Data for about 70 individual TFE and HFB esters are reported. Application of the methodology to a petroleum-derived carboxylic acid concentrate resulted in identification of straight chain, isoprenoid, methyl-substituted straight chain (2-, 3-, 5-,10-, 12-positions along chain), and dimethyl-substituted straight chain acids containing from 11 to 22 carbons. Benzoic acid and homologs with up to 3-carbons in alkyl substitutents were minor components in the sample. The procedure provided for forming TFE and HFB esters from free acids requires less time and effort than a previously reported method, while retaining its capability for achieving essentially quantitative conversion. Free hydroxyl groups in alcohols and phenols are converted to trifluoroacetate esters concurrently with formation of TFE/HFB carboxylic acid esters. The reaction products, including compounds with two functional groups (diacids, salicylic acid, etc.), chromatograph well on conventional nonpolar GC stationary phases.     

Analysis of carboxylic acids in biological fluids by capillary electrophoresis

This review article addresses the different capillary electrophoretic methods that are being used for the study of both short-chain organic acids (including anionic catecholamine metabolites) and fatty acids in biological samples. This work intends to provide an updated overview (including works published until November 2004) on the recent methodological developments and applications of such procedures together with their main advantages and drawbacks. Moreover, the usefulness of CE analysis of organic acids to study and/or monitor different diseases such as diabetes, new-borns diseases or metabolism disorders is examined. The use of microchip devices and CE-MS couplings for organic acid analysis is also discussed.     

Quantum-chemical calculations of the methylation of hydroxamic and thiohydroxamic acids with diazomethane

We made calculations about the methylation of both hydroxamic and thiohydroxamic acids with CH₂N₂. The potential-energy surfaces of several proposed pathways leading to possible site-selective products (N-methylated and O-methylated hydroximates) are presented. Our results agree satisfactorily with an experimental observation by Liguori et al. who found site selectivity in the formation of dimethylated products. Simultaneous deprotonation and methylation occurs in both forms (E and Z) of hydroxamic acid and thiohydroxamic acid, and the net energy barrier via this pathway is the smallest. In most corresponding processes the energy barriers are smaller for thiohydroxamic acid, and the Z-form has an energy barrier smaller than that of the E-form in both hydroxamic and thiohydroxamic acids.     

Esterification of C1−C8 carboxylic acids to n-butyl esters in aqueous solutions for their gas chromatographic analysis

Summary The esterification of C₁–C₈ fatty acid in aqueous solutions and in the presence of sulfuric or hydrochloric acid and with n-butanol is described. It has been established that the esterification can be used for the quantitative determination of these fatty acids in the concentration ratio range of [H₂O]/[n-BuOH]=0.01–5.3. In the concentration ratio range of 0.01–0.8 the water present does not interfere. In the concentration range of above 0.8 anhydrous sodium sulfate is used for binding the water, in the amount of [Na₂SO₄.anh.]/[H₂O]0.2.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids II. Separation of aliphatic carboxylic acids with pyromellitic acid as eluent and with suppressed conductimetric detection

The application of zirconium-modified silica gels (Zr-Silica) as stationary phases for ion-exclusion chromatography with conductimetric detection (IEC–CD) for C₁–C₈ aliphatic carboxylic acids (formic, acetic, propionic, butyric, valeric, caproic, heptanoic and caprylic acids) was carried out using pyromellitic acid as the eluent. Zr-Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. An ASRS-Ultra anion self-regenerating suppressor in the K⁺ form was used for the enhancement of conductimetric detector response of these aliphatic carboxylic acids. A Zr-Silica adsorbed on 10 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in IEC–CD for the separation of these aliphatic carboxylic acids. Excellently simultaneous separation and highly sensitive detection for these aliphatic carboxylic acids were achieved in 25 min by IEC–CD with the Zr-Silica column (250×4.6 mm I.D.) and a 0.2 mM pyromellitic acid containing 0.15% heptanol as the eluent.     

Reversed-phase high-performance liquid chromatography of fatty acid methyl esters with particular reference to cyclopropenoic and cyclopropanoic acids

High performance liquid chromatography of saturated, monounsaturated, diunsaturated, triunsaturated, cyclopropenoic (malvalic and sterculic) and cyclopropanoic (cis-8,9-methylenehexadecanoic and dihydrosterculic) fatty acids was performed with their methyl esters. All separations were carried out with two types of reversed phase columns, the eluent consisting of an acetonitrile/water mixture. The effect of water was studied in the range 0–15%. The best separation was obtained with acetonitrile/water (85:15 v/v). Quantitative results indicated that the detection limits depended upon ultraviolet wavelength and in the present study were 4 ng of methyl sterculate and 125 ng of methyl dihydrosterculate at 195 nm.     

Urea-tetrahydrobenzoxanthene receptors for carboxylic acids

Hydrogen-bonding receptors for carboxylic acids have been prepared based on a cis tetrahydrobenzoxanthene skeleton. X-ray diffraction study of one of these compounds revealed that the cleft is suitable for establishing strong linear hydrogen bonds with the oxygen of a water molecule. Complexes that set only three H-bonds with the guests showed no chiral recognition with amino acid derivatives. However, suitable functionalization of the receptor provided a fourth H-bond with certain amino acid derivatives, leading to significant enantioselective complexation in this case.     

2-Bromoacetyl-6-methoxynaphthalene: A useful fluorescent labelling reagent for HPLC analysis of carboxylic acids

Summary The use of 2-bromoacetyl-6-methoxynaphthalene as a fluorogenic labelling reagent in pre-column derivatization for the HPLC separation of biologically active carboxylic acids (fatty acids and bile acids) has been investigated. The compound reacts (30 min. at 70°C) with carboxylic acids to give fluorescent esters that can be separated by reversedphase HPLC and detected at ex. 300 nm, em. 460 nm. The experimental conditions for the derivatization and chromatographic separation are discussed. Applications to the determination of valproic acid and chenodeoxycholic acid in pharmaceutical formulations are described.     

1,2-Dibromoethane and KI mediated α-acyloxylation of ketones with carboxylic acids

The 1,2-dibromoethane-and Kl-mediatedα-acyloxylation of ketones is reported in moderate to good yield without the use of transition metals and strong oxidants.Various acids are well tolerated with wide functional group compatibility.An 1,2-dibromoethane-and Kl-catalysed reaction mechanism is proposed based on the results of control experiments.     

Trifluoromethanesulfonylimides of arenehydroxamic acids and their aza Lossen rearrangement

Trifluoromethanesulfonylimides of arenehydroxamic acids ArC(NSO₂CF₃)NHOH (1), analogues of arenehydroxamic acids, in which sp² hybridized oxygen atom is replaced by the much stronger electron-withdrawing group NSO₂CF₃, have been synthesized, and the abilities of these compounds to undergo transformations similar to the Lossen rearrangement have been studied.At heating O-trimethylsilyl or O-tosyl derivatives of acids 1 rearrange to carbodiimides ArNCNSO₂CF₃ or products of their hydration, the corresponding carbamides. Interaction of acids 1 with sulfinyl chloride or phosphorus pentachloride results in formation of N-trifluoromethylsulfonyl-N′-arenechloroformamidines, ArNHC(Cl)NSO₂CF₃, which were transformed into their morpholine derivatives and thus characterized.     

The optimized separation of aromatic carboxylic acids by HPLC

The optimization of the separation of eight aromatic carboxylic acids, using Hypersil SAS and MOS reverse phase columns, with respect to eluent (methanol : water) composition, pH, and temperature, is described. Window diagram techniques are used and the pH of the aqueous buffer and elution temperature are shown to be more critical than eluent composition.     

Convenient synthesis of acetaminophen analogues containing α-amino acids and fatty acids via their mixed carbonic carboxylic anhydrides in aqueous organic solvent

Acetaminophen analogues containing α-amino acid and fatty acids were easily synthesized in 77–99% yields from the corresponding mixed carbonic carboxylic anhydrides of α-amino acid and fatty acids using aniline derivatives in aqueous MeCN.     

Silica sulfuric acid-catalyzed expeditious environment-friendly hydrolysis of carboxylic acid esters under microwave irradiation

Silica sulfuric acid was found to be an efficient, recoverable, reusable and environment-friendly catalyst for the fast hydrolysis of various carboxylic acid esters in high conversions and selectivities under microwave irradiation conditions. This protocol has the advantages of no corrosion, no environmental pollution, high reaction rate, high yield, and simple work-up procedure.     

Copper-catalyzed synthesis of aromatic carboxylic acids from arylboronic acids and acetyl acetate

A simple and efficient copper-catalyzed method for the synthesis of aromatic carboxylic acids in moderate to high yields with great functional-group compatibility in the substrates has been developed. The new method uses readily available arylboronic acids and acetyl acetate as the starting materials and inexpensive CuI as the catalyst.