The standard enthalpies of formation of citric and tartaric acids and their dissociation products in aqueous solutions

The energies of combustion of citric and tartaric acids in oxygen were determined by bomb calorimetry. The standard enthalpies of combustion and formation of crystalline citric and tartaric acids were calculated. The heat effects of solution of crystalline acids in water and aqueous potassium hydroxide were determined by direct calorimetry at 298.15 K. The standard enthalpies of formation of acids and their dissociation products in aqueous solution were calculated.     

Comparative 13C NMR study of the conformations of malic and thiomalic acids

Vicinal and geminal ¹³CO₂H? ¹H coupling constants are reported for malic and thiomalic acids at various pH values and related, in a comparative manner, to the known conformational information obtained by ¹H NMR.     

The 13C NMR titration shifts of sulphonic acids

Carbon-13 chemical shifts of a number of alkyl and aromatic sulphonic acids in sulphuric acids in sulphuric acid and strongly basic deuterium oxide have been compared. The titration shifts are relatively small for carbons near the sulphonyl group, but are comparable with those of other organic acids or bases for carbons remote from the deprotonation sites.     

Complexation of citric and tartaric acids with Na and K ions in aqueous solution

The formation of MTar^–, MCit^2– and M₂Cit^– complexes (M is Na⁺ or K⁺) was established in reactions of aqueous solutions of citric and tartaric acids with sodium or potassium chloride solutions; their stability constants were determined by potentiometric titration in aqueous solution at 298.15 K and ionic strength 0.1 and 0.3 mol/l with tetraethylammonium chloride (TEACl) as a supporting electrolyte. Heat effects of reactions between citric acid solutions and sodium or potassium chlorides were measured by calorimetric method at 288.15, 298.15, and 308.15 K and at the ionic strength 0.1, 0.2, and 0.3 M TEACl. The increasing ionic strength was found to decrease exothermic effect of complex formation processes, while the temperature produced the opposite effect. Extrapolation to zero ionic strength was used to find thermodynamic stability constants and standard heat effects of complex formation reactions in solutions of oxyacids. The changes in entropy and heat capacity were calculated as well as standard enthalpies of formation of Na and K complexes of the indicated oxyacids in aqueous solution at 298.15 K.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 253–261.Original Russian Text Copyright © 2005 by Zelenina, Zelenin.     

A new spot test for the detection of traces of citric and tartaric acids in vinegar

A sensitive, new color reaction for the detection of citric and tartaric acids in vinegar has been developed. Acetic anhydride in the presence of trimethylamine has been used as the reagent. Traces of citric (2 μg) and tartaric acid (5 μg) can be detected in concentrated acetic and formic acids.     

13C NMR spectra of bromine derivatives of fatty acids

Summary The¹³C spectra of the methyl esters of the cis and trans isomers of 9,10-dibromostearic, of cis,cis-9,10,12,13-tetrabromostearic, and of 10,11-dibromoundecanoic acid have been obtained, and the assignment of all the signals has been performed. It has been shown that the presence of bromine atoms in the chain of a fatty acid leads to the magnetic non-equivalence of the¹³C nuclei of the methylene groups present at a distance of three carbon-carbon bonds from the nucleus to which the halogen is directly attached. A dependence has been found of the shift parameter of the carbon nuclei in a fatty acid chain on the relative arrangement of the bromine atoms.V. I. Lenin Tashkent State University. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 26–30, January–February, 1977.     

Heteroligand mercury(II) complexes with aspartic,tartaric, and citric acids

Mercury(II) complexes with aspartic (H₂Asp) and tartaric acids (H₂Tart) and heteroligand mercury(II) complexes with H₂Asp, H₂Tart, and citric acids (H₃Cit) were studied by spectrophotometry in aqueous solutions with I = 0.1(NaClO₄) at 20 ± 2°C. It was found that the complexation in both binary and ternary systems depends on the concentrations of the reagents and the pH of the medium. The resulting complexes included [HgAsp], [Hg(OH)Asp]^?, [HgAsp₂]^2?, [HgTart], [Hg(OH)Tart]^?, [Hg(OH)₂Tart]^2?, [HgAspCit]^3?, [HgAspTart]^2?, and [Hg(OH)AspTart]^3?. The logarithms of their stability constants were 11.74 ± 0.12, 20.18 ± 0.17, 20.11 ± 0.10, 5.40 ± 0.11, 15.52 ± 0.09, 24.70 ± 0.12, 19.19 ± 0.12, 14.55 ± 0.16 and 23.80 ± 0.14, respectively. The experimental data were analyzed in terms of the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow one to consider only those species that are sufficient for accurate reproduction of the observed pH-dependence of the optical density.     

Investigation of the structure of aminodicarboxylic acids by 13C NMR method

The protonation of ethylenediaminedisuccinic acid was investigated over a wide range of pH by the ¹³C NMR method. The degrees of protonation of the donor groups and the fractions of the trans and gauche conformers in the partially and fully protonated forms of this complexone were determined. A comparison is made of the conformational states of aspartic, iminosuccinic, and ethylenediaminedisuccinic acids. It is shown that complication in the structure has an effect on the conditions of the trans-gauche transitions, which determine the form of the ligand most favorable for combination with the metal ion.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 4, pp. 499–504, July–August, 1989.     

[13C]NMR study of naphthoflavones

The [¹³C]NMR spectra of α-,β- and γ-naphthoflavones were assigned at 25.2 MHz resorting to models such as the unsubstituted flavone and appropriate substituted acetylmethoxynapthalenes. Supporting evidence for the assignments was provided by gated decoupled spectra and all the chemical shifts in the 11 compounds studied gave a self-consistent data set.     

N-Oxides of polychloropyridines.13C NMR study

The effect ofN-oxidation of a series of polychloropyridines on¹³C NMR parameters has been studied. It has been established that inN-oxides of polychloropyridines an electric field through-space effect of theN-oxide group predominates in the shielding of the -carbon atom compared to the other carbon atoms. A linear correlation between¹³C NMR chemical shifts and total charge densities calculated by the MNDO method for the carbon atoms ofN-oxides of polychloropyridines has been found.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2425–2428, December, 1995.The authors are grateful to V. V. Kolchanov for help in the synthesis of compounds under study.     

A 13C NMR spectroscopic study of the phase transitions of alkane dicarboxylic acids in the solid state

¹³C NMR spectra of a few odd-member alkane dicarboxylic acids such as glutaric and pimelic acids have been studied across their phase transitions. The spectra provide clear evidence for the structural changes accompanying the transitions. In the case of malonic acid, the study establishes that the two carboxyl units are equivalent in the high-temperature phase unlike in the other odd-member dicarboxylic acids where they are non-equivalent.     

13 C NMR spectroscopy of substituted xanthones—II: 13C NMR spectral study of polyhydroxy xanthones

The ¹³C NMR chemical shifts of eleven hydroxy-, two hydroxymethoxy xanthones, and xanthone-C-glucoside, mangiferin, are presented and analyzed. Hydroxy substituent effects depending on substituent position as well as on shielded ring carbon position have been evaluated. Hydroxy substituent increments for xanthones are proposed. Effects of hydroxylation on carbonyl carbon shift and the methylation of hydroxy group and the corresponding shift increments which are of diagnostic value have been observed and discussed.     

Solvent effects on the dissociation reactions of tartaric, maleic and phthalic acids; comparative study and analysis of thermodynamic functions

The first and second dissociation constants of tartaric, maleic and phthalic acids have been determined using EMF method in water-ethanol mixed solvents, over a wide range of solvent composition (0-60 wt% ethanol) at six different temperatures (ranging from 30 to 55 degrees C at intervals of 5 degrees C). The thermodynamic parameters (DeltaG degrees , DeltaH degrees and DeltaS degrees ) for the first and the second ionization reactions were calculated from the well known equations. The results have been discussed in terms of the solute-solvent interactions and were compared with those of malic, malonic and succinic acids in the same mixed solvents.     

13C NMR spectral study of polyacetoxyxanthones. IV—13C NMR spectroscopy of substituted xanthones

The ¹³C NMR chemical shifts of nine acetoxyxanthones are reported and identified. The acetoxy substituent effects have been evaluated and the corresponding shift increments proposed.     

Simultaneous determination of ascrobic,citric, and tartaric acids by potentiometric titration with PLS calibration

The partial least squares (PLS) modeling method was used in the analysis of mixtures of ascorbic, citric, and tartaric acids by potentiometric titration. Binary mixtures of tartaric and citric acids, as well as ternary mixtures of tartaric, citric, and ascorbic acids, were titrated by sodium hydroxide pH-metrically. The linear relationship between the volumes of titrant and the concentrations of analytes was obtained by PLS regression. The designed model was then used to predict the concentrations of components in unknown samples. The practical utility of this method was demonstrated for the simultaneous determination of acids in binary and ternary mixture systems within concentration range from 4 × 10⁻⁴ to 2 × 10⁻³ M, and acceptable results were obtained. The text was submitted by the authors in English.     

The13C NMR, UV and IR absorption spectra of pyridinedicarboxylic acids

The¹³C NMR, UV and IR absorption spectra of 2,3-, 2,4-, 2,5-, 2,6-, 3,4-, and 3,5-pyridinedicarboxylic acids were recorded and their spectral parameters were assigned. The influence of electronic properties of the substituents on the direction of the chemical shifts is discussed. The influence of substituents in the molecule on _max and _max of the UV-spectral band is disscused. Analizing¹³C NMR, UV, and IR absorption spectra it was found that there is a disturbance of mutual electronic interaction of substituents by a steric ortho effect. This effect is reflected in paramagnetism of the carboxyl group, the value of the correlation coefficient, deformation C–O stretching bands, and the decrease in the intensity of the CT band.Department of Organic Chemistry, University of Economics, PL-53 342 Wroclaw, Poland, Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 210–218, February, 1999.     

13C NMR study of some polychloro-isobutane and -isobutene compounds

The ¹³C chemical shifts and the carbon–proton coupling constants have been determined for some chlorinated isobutane and isobutene compounds. The one-bond coupling constants in isobutane derivatives showed a regular increase with an increasing number of γ-chlorine substituents. The three-bond coupling constant of the methyl carbon decreased from 4.2 to 2.0 Hz as the number of chlorine substituents in the γ-position increased. In the isobutene compounds, the vicinal coupling of C-1 was larger to protons in a group that is trans with respect to a chlorine substituent on C-1 than to those in the corresponding group cis to the chlorine. The vicinal coupling constants between atoms in geminal groups (on C-2) seem to be affected by the orientation of the chlorine substituent on C-1.     

13C NMR study of 2,3,4,5-tetraphenylsilole dilithium salt

The complete assignment of the signals in the¹³C NMR spectra of 2,3,4,5-tetraphenyl-1-R¹,R²-1-silacyclopenta-2,4-dienes (R¹=R²=H, Me) and of the dianion of lithium salt [(PhC)₄Si]²⁻·2Li⁺ was carried out by 2D NMR spectroscopy. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 216–218, January, 1999.     

High-resolution solid-state 13C NMR study of ethylcellulose films

Ethylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including ¹H spin-lattice relaxation time (T_1H), rotating-frame ¹H spin-lattice relaxation time (T_1ρH), and ¹³C spin-lattice relaxation time (T_1C). The values of T_1ρH for carbons in the glucose units of ethyl-cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values of T_1C for unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. The T_1C values for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wiley & Sons, Inc.