Aliphatic Carboxylate Ions Research Articles

Decarboxylative photosubstitution of dicyanobenzenes with aliphatic carboxylate ions

The photoreaction of dicyanobenzenes with aliphatic carboxylate ions afforded alkylcyanobenzenes and alkyldicyanobenzenes via decarboxylative substitution. The redox-photosensitized reaction system was effective in improving the product yield. The efficiency of this photoreaction depended on the structure of the carboxylate ion, and the product distribution varied with the dicyanobenzenes employed. This photoreaction was proved to be a clean process for the preparation of alkylcyanobenzenes.

Unimolecular Rearrangements of Transient Carboxy Radicals and Cations

Charge reversal (CR) and neutralization–reionization (NR) mass spectra of aliphatic carboxylate ions RCOO– provide insight into the behaviour of the transient neutral carboxy radicals RCOO• as well as the short-lived RCOO+ cations. For the neutral radicals, a novel hydrogen rearrangement is proposed, which might explain the sometimes only modest yields in the Hunsdiecker reaction of carboxylic acids in the condensed phase.

Intercalation of Aliphatic Carboxylates in Hydrotalcite Interlayers: Selective Photochemical Hydrogen Abstraction by Benzophenonecarboxylate

Abstract The photochemical hydrogen abstraction of p-benzoylbenzoate ions (BPC) from aliphatic carboxylate ions in LDH (hydrotalcite) interlayers yielded a series of their 1:1 adducts. The product distributions were rather selective as well as distinctive from those of sodium salts and methyl esters in homogeneous solutions without LDH. These results have been discussed on the basis of their mutual disposition on the layer surfaces of the LDH.

Formation of Organic Anion-pillared Layered Zinc Hydroxides by Coprecipitation.

From the viewpoints of removal, recovery and preconcentration of organic anions (An-) in water, the direct fixation into the precipitates of layered zinc hydroxide by a coprecipitation has quantitatively been investigated. When the solution of 8-200 mmol dm-3 Zn (NO3)2 was added dropwise into the solution of 1-250 mmol dm-3 organic anions at 25°C with stirring, the saturated aliphatic carboxylate ions with long carbon chain such as sebacate and dodecanedioate, the aromatic carboxylate ions such as terephthalate and also the anionic surfactants such as dodecylbenzenesulfonate and dodecyl sulfate were incorporated highly in the layered zinc hydroxide precipitates. The optimum conditions were found as follows; Z n2+/ A 2- molar ratio:>1.6, Zn2+/A- molar ratio> 3.2, and pH 6-7. The pecipitates were also found to have the layer structure with large basal spacings, which crystallinity being quite high in spite of the low reaction temperature. The guest organic anions were thought to be incorporated in a perpendicular or tilted configuration to the zinc hydroxide layers or botallackite type layers as a monolayer or bilayer by coordinating their anionic functional group, to Zn2+ ion in the host layers. Therefore, if the solutions contained a lot of inorganic anions, the coprecipitation of the organic anions was not influenced and the excellent selectivity for organic anions was observed. In conclusion, the possible fixation method based on the new mechanism (coprecipitation as pillared-layered zinc hydroxides) can be proposed.

Structure-reactivity correlations in the reaction of ethyl bromoacetate with aliphatic carboxylate ions

The second-order rate constants at three different temperatures have been determined for nucleophilic substitution reactions of ethyl bromoacetate with various substituted aliphatic carboxylate ions (XCH2COO−) in 90% acetone-10% water (v/v) mixture and the activation parameters have been evaluated. The rate data have been analysed in terms of electronic and steric effects by using various single and multi-parameterequations. Analysis of the results shows that localized and steric effects are more important than the delocalized effect. The regression coefficient of the inductive component is negative indicating that inductively electron-releasing substituents accelerate the reaction and electron-withdrawing substituents retard it. The steric component corresponds to the reaction being subject to steric acceleration by the substituents. The per cent steric effect has been calculated. The Bronsted type correlation is fair, and theβN value has been determined.

A novel method for the direct derivatization of straight-chain aliphatic carboxylates after trapping on anion-exchange resin

A novel procedure for the characterization of traces of lipophilic straight-chain aliphatic carboxylate ions in aqueous samples is described. The carboxylates are adsorbed on an Amberlyst A26 [Cl -] resin column. The resin is then dried and suspended in methyl iodide at room temperature. A gas Chromatographic analysis of the methyl iodide solution allows the determination of the carboxylates as their methyl esters. Full characterization of each carboxylate with an overall recovery over 84% from 1 ppm aqueous sample solutions is attained.

Evidence from inelastic electron tunnelling spectroscopy for vibrational mode reassignments in simple aliphatic carboxylate ions

Tunnelling studies of the vibrational spectra of formate- and acetate-, including 18O-enriched acetate-, anions adsorbed on plasma-grown aluminium and magnesium oxide surfaces show that the CO 2 − symmetric stretch mode can be clearly distinguished from the CH modes in the same region of the spectra. This CO 2 − mode of the formate ion is at 1456 cm −1 on aluminium oxide and at 1348 cm −1 on magnesium oxide; for the acetate ion the corresponding values are 1463 and 1445 cm −1

Permeability of mono-carboxylate ions across an anion exchange membrane

Transport numbers of several aliphatic and aromatic carboxylate ions across an anion exchange membrane were determined on the basis of the transport number of the co-ions across the membrane in electrodialysis. Also, the specific conductivity and water content of each carboxylate ionic-form membrane were measured. The transport number of lower aliphatic carboxylate ions decreases slowly with increasing molecular weight, but it decreases markedly where the carbon number is over five. In particular, the transport number of caprylate or of caprate ions is below 0.5, and these ionic-form membranes apparently lose the characteristics of an anion exchange membrane. For aromatic carboxylate ions, the benzoate ion a higher transport number, but p- or O-hydroxybenzoate ions only about 0.6. The specific conductivity and water content of each carboxylate ion having a lower transport number are very small compared with other carboxylate ions of higher transport number. This suggests that the hydration number and the activity of ions with a lower transport number are small in anion exchange membranes.

An electron spin resonance study of reactions of carboxylic acids with the sulphate radical-anion

Radicals which mediate in the reactions of aliphatic carboxylate ions with the sulphate radical-anion, generated from the TiIII–K2S2O8 couple, have been observed by e.s.r. spectroscopy. Both oxidative decarboxylation (RCO2–→ R˙) and hydrogen-atom abstraction from C–H occur. The behaviour of SO4–˙ is compared with that of ·OH.

Reversible Inhibition of the Esterase Activity of Carboxypeptidase A by Carboxylate Anions

Reversible inhibition of the hydrolysis of O-(hippuryl)-L-3-phenyllactic acid by carboxypeptidase A has been studied for 26 carboxylate ion inhibitors at 25°, pH 7.5, and ionic strength 0.2 (NaCl). Competitive inhibition, partially competitive inhibition, and mixed inhibition kinetics were observed. Within homologous series, strictly competitive inhibition by the lower members gave way to partially competitive inhibition with higher members, while homologs having very large hydrocarbon moieties displayed mixed inhibition kinetics. Partially competitive inhibition in this system is not consistent with a scheme involving only 1:1 enzyme–inhibitor complexes; rather, higher order enzyme–inhibitor complexes will be necessary for a complete description of the inhibition mechanism.Inhibition constants (log Ki) for the aliphatic carboxylate ions which are strictly competitive inhibitors, are closely correlated linearly with Hansch's π-parameter for hydrophobicity. This quantitatively confirms the importance of hydrophobic interactions between carboxypeptidase A and inhibiting ions. Carboxylate ions containing aromatic rings are less effective inhibitors than expected on the basis of the π-parameters of their hydrocarbon moieties. The dependence of log Ki on π in this system is unusually strong for a binding phenomenon, and suggests that an inhibitor-dependent conformational change may also be involved.

Absorption spectra of neodymium carboxylate complexes

Variations in absorption spectrum of the Nd 3+ ion on complex formation with aliphatic carboxylate ions have been examined spectrophotometrically and an attempt made to correlate band shift with thermodynamic complexity constants. With mono- and α-carboxylic acids as the complexing ligands, shift of the Nd 576 mμ band to lower frequencies is approximated by changes in the free energy of the complexes formed. With dibasic and higher carboxylic acids the reverse is observed, band shifts towards lower energy levels being associated with increasing values of Δ A. No definitive explanation is presented for this anomaly; but dsp-hybridization, with possible involvement of 4-f electrons, is considered a feasible reason.