Aliphatic Carboxylic Esters Research Articles

Catalyst- and Stoichiometry-Dependent Deoxygenative Reduction of Esters to Ethers or Alcohols with Borane-Ammonia.

A facile and selective room temperature deoxygenation of both aromatic and aliphatic carboxylic esters to ethers has been achieved by regulating the stoichiometry of the reductant, BH3-NH3, and the catalyst, TiCl4. This first, practical borane-mediated process is compatible with various potentially sensitive functional groups and is applicable to the deoxygenative ether formation from typically challenging aromatic acid esters. Substituting BF3-Et2O as the catalyst alters the reaction pathway, reducing the esters to alcohols. Mechanistic insights are provided by NMR spectroscopy, deuterium labeling, and kinetic isotope studies.

The uropygial gland of the Great Cormorant (Phalacrocorax carbo): II. Biochemical analysis of the uropygial secretion

In contrast to many other water birds, the Great Cormorant, Phalacrocorax carbo (Phalacrocoracidae), shows a typical wing-spreading behavior after diving. This behavior has been linked to the partial wettability of the Cormorant’s feathers based on the unusual structure of the contour feathers. Close to the rachis, these feathers have a closed vane with very densely spaced barbs but have an open vane in more peripheral feather parts. To investigate whether the wettability is connected to the composition of the uropygial gland secretion that is often linked to water repellency of bird feathers, we analyzed the gland secretions of the Great Cormorant and, for comparison, of the Muscovy Duck, Cairina moschata (Anatidae). Using the mass spectrometry techniques, atmospheric solids analysis probe-atmospheric pressure chemical ionization-mass spectrometry (ASAP-APCI-MS) and gas chromatography/mass spectrometry (GC/MS), significant differences in the chemical composition of the secretions were revealed. The Cormorant showed a highly diverse mixture of more than 1000 compounds consisting of methyl-branched aliphatic carboxylic esters with large chain length variability. In contrast, the duck’s secretion is dominated by the two esters octadecyl and eicosyl 2,4,6-trimethyloctanoate. Water contact angle measurements of the secretions showed that the secretion of the Muscovy Duck has higher water repellency than that of the Great Cormorant. Nevertheless, contact angle measurements of feathers before and after removing of feather waxes indicate that these waxes, likely consisting of the uropygial gland secretions, did not influence water repellency of the feathers to a large degree.

Ruthenium complexes of tetradentate bipyridine ligands: highly efficient catalysts for the hydrogenation of carboxylic esters and lactones

A new type of readily available, air-stable ruthenium complex of tetradentate bipyridine ligands has been developed. These complexes displayed exceptional efficiency for the hydrogenation of aromatic and aliphatic carboxylic esters and lactones at as low as 10 ppm catalyst loading under very mild conditions.

Predicting Solvent Stability in Aprotic Electrolyte Li–Air Batteries: Nucleophilic Substitution by the Superoxide Anion Radical (O2•–)

There is increasing evidence that cyclic and linear carbonates, commonly used solvents in Li ion battery electrolytes, are unstable in the presence of superoxide and thus are not suitable for use in rechargeable Li-air batteries employing aprotic electrolytes. A detailed understanding of related decomposition mechanisms provides an important basis for the selection and design of stable electrolyte materials. In this article, we use density functional theory calculations with a Poisson-Boltzmann continuum solvent model to investigate the reactivity of several classes of aprotic solvents in nucleophilic substitution reactions with superoxide. We find that nucleophilic attack by O(2)(•-) at the O-alkyl carbon is a common mechanism of decomposition of organic carbonates, sulfonates, aliphatic carboxylic esters, lactones, phosphinates, phosphonates, phosphates, and sulfones. In contrast, nucleophilic reactions of O(2)(•-) with phenol esters of carboxylic acids and O-alkyl fluorinated aliphatic lactones proceed via attack at the carbonyl carbon. Chemical functionalities stable against nucleophilic substitution by superoxide include N-alkyl substituted amides, lactams, nitriles, and ethers. The results establish that solvent reactivity is strongly related to the basicity of the organic anion displaced in the reaction with superoxide. Theoretical calculations are complemented by cyclic voltammetry to study the electrochemical reversibility of the O(2)/O(2)(•-) couple containing tetrabutylammonium salt and GCMS measurements to monitor solvent stability in the presence of KO(2)(•) and a Li salt. These experimental methods provide efficient means for qualitatively screening solvent stability in Li-air batteries. A clear correlation between the computational and experimental results is established. The combination of theoretical and experimental techniques provides a powerful means for identifying and designing stable solvents for rechargeable Li-air batteries.

ChemInform Abstract: Selective Cleavage of Carboxylic Esters in the Presence of Monosubstituted Malonates.

Abstract Aliphatic carboxylic esters containing in the molecule a malonate moiety with an α-hydrogen undergo selective cleavage in the presence of potassium tertbutoxide in wet tetrahydrofuran. Dedicated to Professor Paul Dowd on the occasion of his 60th birthday.

Organic constituents of cruds in Cu solvent extraction circuits.: I. Separation and identification of diluent-soluble compounds

Interfacial `cruds' from hydrometallurgical solvent extraction of copper ions were examined to assist in the establishment of potential causes of cruds. Diluent-insoluble, polar organics comprised the majority of the solid mass of crud; inorganic particulates and bacterial/fungi were not dominant. Procedures involving ultracentrifugation and acetone extraction were developed to separate these cruds into inorganic, soluble organic, and insoluble organic fractions, and were used to analyze 12 assorted extraction stage and strip stage cruds. UV–Visible and infrared spectroscopic comparisons of the materials with known standard alkarylhydroxyoxime (AAHO) reagents and hydrolysis products were made. Two cruds were further examined by thin layer chromatographic (TLC) separation. Cruds contained larger proportions of de-oximated AAHO than did the supernatant organic phase. Strip stage cruds contained more de-oximated AAHO, relative to the AAHO reagents, than did the respective extraction stage cruds. Cruds contained larger proportions of aliphatic carboxylic acids and aliphatic carboxylic esters, than did the respective supernatant organic solutions. Copper complexes of AAHO reagents were not concentrated in the crud. The polarity of the diluent-insoluble organics was reflected in TLC behavior. Diluent-insoluble organics contained large amounts of carboxylic acids and esters. In experimental trials of the reconstitution of crud from decanted organic and aqueous phases, added diluent-insoluble organics obtained from crud were required for the reconstitution of crud, whereas inorganic particulates were not required. Inorganic particulates were incorporated into the reconstituted crud, but did not reconstitute crud in the absence of diluent-insoluble organics. It was hypothesized that low-polarity, diluent-soluble compounds are less likely to cause crud episodes, or even to be accumulated in crud, than are the diluent-insoluble organics.

Selective Cleavage of Carboxylic Esters in the Presence of Monosubstituted Malonates

Abstract Aliphatic carboxylic esters containing in the molecule a malonate moiety with an α-hydrogen undergo selective cleavage in the presence of potassium tertbutoxide in wet tetrahydrofuran. Dedicated to Professor Paul Dowd on the occasion of his 60th birthday.

Radiolysis mechanisms in clathrates systems: EPR spectroscopy investigation of the long chain carboxylic esters urea adducts

The mechanism of the gamma radiolysis of long chain aliphatic carboxylic esters from decanoic and hexadecanoic acids, in the state of urea clathrates has been investigated by EPR spectroscopy. The major species identified are the carboxylate anion-radicals, trapped electrons, and the neutral primary alkyl radicals of type RCH · 2 arising from the OC and CCOOR bond scissions. Also present among the species trapped at 77 K are the secondary alkyl radicals CH 2CHCH 2 formed by CH bond rupture in the aliphatic chains. On warming the radical anions are converted into RCH · 2 species and intermediate acyl type radicals RCO have been observed. At room temperature all the primary and secondary radicals gradually disappear, being partially converted into the α-carboxylate radicals RCH 2CHCOOR. This process is thought to involve the intrachain migration of the free valences by hydrogen abstraction. The comparison with the neat compounds has shown that the clathrate structure has a profound influence on the radiolysis mechanism the major effects observed being the increase of the OC scission products, the increase of the radical anions yield and the decrease of the CH bond ruptures in the aliphatic chains.

Electroorganic chemistry. 138. Electrochemically promoted cyclocoupling of 1,3-dienes or styrenes with aliphatic carboxylic esters

The cathodic cyclocoupling of 1,3-dienes 1 with aliphatic esters 2 in promoted by a magnesium electrode and yields homologs of 3-cyclopentenol. Under similar reaction conditions, the coupling of styrenes with 2 affords 2-phenylcyclopropanol derivatives, and this coupling reaction has been successfully applied to the synthesis of ar-dihydroturmerone and curcumone

Hierarchical ascending classification of Kováts retention indices as a means of indicating siloxane stationary phase specificities towards aliphatic carboxylic esters

Hierarchical ascending classification was applied to the Kováts retention indices of 175 aliphatic unsaturated and saturated carboxylic esters determined on fourteen siloxane stationary phases. This method of data processing helps to compare and to delineate the relative specificities of the different stationary phases. The role of structural effects in this homogeneous population of aliphatic esters and the specific character of certain stationary phases towards sub-classes of compounds with branching or carbon—carbon double bonds in the alcohol or acid chains of the esters are presented.

INDO-MO conformational study of cyclic α-acyloxy radicals derived from -γ-lactones

Abstract As an extension of earlier comprehensive INDO-MO-SCF studies in this laboratory of acyclic, aliphatic carboxylic-ester radicals, we present the results of a similar INDO-based conformational investigation of analogous cyclic α-acyloxy radicals, where R is H or CH3, for which isotropic EPR proton splitting-constant data over the temperature range 10–40°C are recently available. This investigation shows that we may successfully account for the observed EPR data, in each of these radicals, in terms of nonplanarity at the radical site accompanied by rapid inversion, out-of-plane vibration of the C α R bond, and envelope-type ring motion.

ChemInform Abstract: SYNTHESIS OF ESTERS OF PHOSPHONOFORMIC ACID AND THEIR ANTIHERPES ACTIVITY

AbstractSynthetisiert und auf Antiherges‐Wirkung untersucht werden die Phosphorverbindungen (I)‐(III).

Steric hindrance in synthesis : Dealkylation of hindered carboxylic esters via the action of organolithium reagents. synthetic and mechanistic aspects

The reaction of n-propyllithium with a number of hindered aliphatic carboxylic esters in ether at 0° produces cleanly the corresponding carboxylic acid in satisfactory yields. This reaction represents a facile dealkylation of hindered carboxylic esters. The mechanistic aspects are briefly examined.

The degradative versatility, arylesterase activity and hydroxylation reactions of Acinetobacter lwoffi NCIB 10553.

Summary. A study of the range of organic compounds utilized as sole carbon source by Acinetobacter lwoffii NCIB 10553 indicates that the organism is Acinetobacter A2 in the classification of Baumann, Doudoroff & Stanier (1968). NCIB 10553 resembles NCIB 8250 (‘Vibrio 01′, described by Fewson, 1967a, b). NCIB 10553 adapted to utilize acetylsalicylate does not grow with the lower n‐alkanes, whereas it does utilize some sugars, although after a lag, and grows readily on a number of aromatic and aliphatic carboxylic esters, including triglycerides, natural oils and fats and other compounds of pharmaceutical interest. Cell‐free extracts readily hydrolyse fatty acid esters of the mono‐ and dihydroxybenzoates and of catechol, quinol, phenol and p‐nitrophenol. They also simultaneously hydroxylate and decarboxylate salicylate, 2,3‐, 2,4‐, 2,5‐ and 2,6‐dihydroxybenzoate but only in the presence of NADH (or NADPH) and FAD. Some other aromatic acids are slowly oxidized under these conditions.

Intramolecular hydrogen rearrangement associated with bond dissociation in field ion mass spectrometry

Use of the electric sector field as an energy filter provides a valuable means for studying gas-phase decompositions of metastable organic ions in double-focusing mass spectrometers. Based upon this principle, a “decoupling technique” was employed to analyse time requirements and gas-phase origin of rearrangement processes in molecular ions generated by field ionization. While in earlier studies gas-phase rearrangement was generally found to be slow (too slow to yield “normal” fragment peaks in single-focusing field ion mass spectrometers) it was established that elimination of RCOOH from aliphatic carboxylic esters can involve exceedingly fast hydrogen rearrangement prior to, or concomitant with, CO bond dissociation, i.e., that the combination of these two events can take place within a very short time interval (10 −1210 −11 sec) after ionization. In several cases the rearrangement products C nH 2n + can attain such prominence as to present the base peaks in the field ion mass spectra in contrast to molecular ions of unusually low abundance. The ease of these rearrangement processes is discussed in view of prerequisites concerning transition states as well as site specificity in comparison to equivalent electron-impact induced fragmentation of this class of compounds,

The carbonyl group frequency. Part II. Aliphatic carboxylic esters

The carbonyl group frequencies of the series of methyl-substituted methyl acetates have been measured. As methyl substitution into the acyl or alkoxy-group increases, the frequencies, for vapours and solutions in non-polar solvents, decrease smoothly. These frequencies are well correlated by the sum of the Taft σ*-constants of the two alkyl groups, and this correlation can be extended to the frequencies of carboxylic acids. The less regular behaviour observed in polar solvents is ascribed to the importance of steric effects for t-butyl esters. The low solvent sensitivity of the carbonyl frequencies of t-butyl pivalate and isobutyrate is attributed to steric hindrance of specific solvation; conversely, the greater sensitivity of t-butyl acetate to polar solvents can arise from preferential solvation of the ester in the s-trans-conformation. The ability of esters to form hydrogen bonds with pyrrole, as measured by the bonded N–H stretching frequencies, is proportional to their carbonyl frequencies and is largely governed by the polar effects of the alkyl groups; for hydrogen bonding with phenol, steric effects become important for esters other than acetates.

A STUDY BY ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY OF RADICALS FORMED FROM ACETAMIDE AND FORMAMIDE

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EPR Spectroscopic Study of Radicals Formed from Aliphatic Carboxylic Esters and Related Compounds

A long-range coupling across the alkoxycarbonyl group of about 1.4–1.5 G has been observed in the EPR spectra of radicals formed in the hydroxyl-radical-initiated homopolymerization of methyl acrylate, ethyl acrylate, and methyl methacrylate within an aqueous flow system at 25°±1°C. This coupling has been further investigated by way of a comprehensive EPR study of a series of simpler, related radicals prepared under similar conditions from methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, and methyl isobutyrate by hydrogen-atom abstraction with hydroxyl radicals. For ester radicals other than those produced from the formates there was a long-range coupling of 1.4–1.5 G with protons δ to the unsaturated carbon atom when this unsaturated carbon atom was adjacent to the oxycarbonyl group, i.e., for radicals with the following functional structures, Ċ–CO–O–C and C–CO–O–Ċ. The two formates yielded only the radicals HCOOĊH2 and HCOOĊHCH3. These displayed a γ coupling with the formyl proton of 2.4–2.5 G. All these results are shown to be compatible with a simple model based on a delocalized π-bond system. Comparison of the observed proton coupling constants with the available data for similar unsubstituted aliphatic radicals suggests that the value of Qα in the McConnell equation aα=Qαρ is significantly lower in a conjugated radical than in a similar nonconjugated radical. In support of the data from this study of hydroxyl-radical attack on esters, the substrates formic, acetic, propionic, n-butyric, and isobutyric acids and methanol, ethanol, and acetone have been examined in a like fashion. Many of the esters and acids investigated underwent hydrogen-atom abstraction at more than one site. For those substrates, it was possible to estimate qualitatively the selectivity of hydroxyl-radical attack from the relative intensities of the EPR absorptions of the different reaction products. The results so obtained are reckoned to generally support the expected electrophilic character of the hydroxyl radical in these reactions.

Physical properties and chemical constitution; aliphatic carboxylic esters.

Physical properties and chemical constitution; aliphatic carboxylic esters.