Carboxylic Acid Proton Research Articles

The Preparation and Crystal Structure of Polymeric Anhydrous Sodium Hydrogen o-Phenylenedioxydiacetate

The crystal structure of anhydrous sodium hydrogen o-phenylenedioxydiacetate , [Na2( Hbdda )2]n, has been determined by X-ray methods and refined to a residual R 0.031 for 1234 observed reflections. Crystals are monoclinic, space group C2/c with Z 4 in a cell of dimensions a 18.415(6), b 7.4667(7), c 16.354(7) � ,β112.61(2)�. The dimeric repeating unit has two centrosymmetrically related pentagonal pyramidal Na-O6 complex centres [Na-0, 2.272-2.439(2) � ] bridged by carboxylate oxygens. The pentagonal plane comprises four oxygens from the Hbdda ligand as well as one providing the bridging link. The axial bond gives the step-polymer link while the carboxylic acid proton is hydrogen bonded to a carboxylate oxygen of the inversion-related Hbdda ligand [O…O, 2.469(2) � ].

1H and 13C NMR studies on the self‐association of retinoic acid

AbstractThe monomer–dimer equilibrium of retinoic acid in carbon tetrachloride was studied by 1H and 13C NMR spectroscopy. The dimer dissociation constant at 24°C was determined to be 0.38 mM from a fit of the changes in the carboxylic acid carbon chemical shift as a function of concentration. The temperature dependence of the equilibrium constant obtained from the 13C NMR signals was used to determine the enthalpy (8.0 kcal mol−1) and entropy (12 cal mol−1 K−1) changes for the dimer dissociation process. These results were shown to be more precise than the values obtained from the carboxylic acid proton resonance.

ChemInform Abstract: Protonation of Carboxylic Acids (I) by Hydrogen Bromide in Dibromodifluoromethane: Rates of Proton Exchange, Relative Basicities, and the Acidity of HBr‐CBr2F2.

ChemInform Abstract: Protonation of Carboxylic Acids (I) by Hydrogen Bromide in Dibromodifluoromethane: Rates of Proton Exchange, Relative Basicities, and the Acidity of HBr‐CBr2F2.

Protonation of carboxylic acids by hydrogen bromide in dibromodifluoromethane: rates of proton exchange, relative basicities, and the acidity of HBr–CBr2F2

Ethanoic, propanoic, butanoic, 2,2-dimethylpropanoic, phenylethanoic, and benzoic acids are fully protonated by HBr–CBr2F2, and at low temperatures (<168 K) separate 1H n.m.r. signals for HBr and RCO2H2+ are observed. If the temperature is reduced even further then resolution of the two acid proton signals of the latter may be observed. Dichloroethanoic and trichloroethanoic acids are not protonated by this acid system. 2-Chloropropanoic acid may be partly protonated. Line-shape analysis of the n.m.r. spectra at low temperatures has been used to determine the rates of proton exchange between HBr and RCO2H2+, and in this way an assessment of the relative basicities of the carboxylic acids is obtained. The behaviour of HBr–CBr2F2 is compared with superacid systems.

Compositional analysis of styrene‐acrylic acid copolymers by 1H NMR

Abstract1H NMR analysis of low molecular weight styrene‐acrylic acid (St/AA) copolymers is described. Three approaches to copolymer composition determination were evaluated and these include: (i) use of the signal for the carboxylic acid protons of the original copolymers, (ii) formation of the ammonium salt of the copolymers and then use of the signal for the ammonium protons, (iii) exchange of the ammonium protons with deuterium (…COONH4 + 4D2O → … COOND4 + 4DOH) and use of the signal for the proton on DOH to estimate the number of acid groups in the original copolymer sample.

Evaluation of MNDO calculated proton affinities

AbstractA large set of charged species arising mainly from protonation or deprotonation of hydrocarbons, alcohols, ethers, carboxylic acids, amines, imines, and nitriles has been studied by means of the semiempirical self‐consistent‐field (SCF) molecular orbital (MO) MNDO method. From the calculated heats of formation of such charged species and those of neutral molecules, MNDO‐estimated proton affinities have been obtained and the results compared with experimental gas‐phase proton affinities. If the small size anions and acetylides, for which the method predicts heats of formation too large, are ruled out, the mean absolute error in calculated proton affinities is ca. 7 kcal/mol for hydrocarbons (22 acid‐base pairs) and ca. 8 kcal/mol for oxygen‐containing compounds (25 acid‐base pairs). For nitrogen‐containing molecules it is necessary to discard, in addition, the values corresponding to the protonation of alkylamines and imines in order to achieve a reasonable mean absolute error of 7–8 kcal/mol.

Basicity and metal ion binding capability of amine-carboxyboranes, R 3N·BH 2COOH, boron analogs of glycine and N-methylated glycines

Ionization of the carboxylic acid proton from net zero charged amine-carboxyboranes, where amine = NH 3, CH 3NH 2, (CH 3) 2NH, and (CH 3) 3N, occurs with pK a values of 8.33, 8.23, 8.14, and 8.38, respectively, at 0.5 M ionic strength and 21 °C. There is no evidence for amine nitrogen deprotonation in the first three compounds at pH < 11. In contrast to glycine and its mono- and di-N-methylated derivatives, the boron analogs do not chelate Zn 2+ or Cu 2+. Up to pH 11, both metal ions coordinate to the four amine-carboxyboranes only through the carboxylate group. For the binding of Zn 2+, the respective stability constants logarithms are : 2.47, 2.43, 2.32, and 2.67.

Kinetics and mechanisms of redox reactions in aqueous solution. Part 7. Decarboxylation of aliphatic acids by aquasilver (II) ions

The overall reaction 2AgII+ RCO2H → 2AgI+ 2H++ CO2+ products has been studied at different acidities (1.0 ⩽[HClO4]⩽ 4.0 and I= 4.0 mol dm–3) and temperatures (283 ⩽T⩽ 303 K). The rate slightly increases (18%) with increasing [AgI] within the range investigated. The rate-limiting reactions are the electron transfers from the carboxylic acids to Ag2+(aq) and [Ag(OH)]+(aq). The decrease in rate with increasing [H+] is considered to be due to the formation of the unreactive RCO2H2+ species as a result of protonation of the carboxylic acids. This assumption is more plausible than an earlier one favouring carboxylate anion as the reactive entity in solutions of acid at between 1.0 and 4.0 mol dm–3 HClO4 because KcKa where Kc and Ka are respectively the protonation and dissociation constants of the carboxylic acid. The rate constants with Ag2+(aq) and [Ag(OH)]+-(aq) may be correlated with Taft σ* values giving ρ values of –10.7 ± 0.7 and –9.8 ± 0.4 respectively. The thermodynamic parameters corresponding to the rate-limiting electron transfer to Ag2+(aq) and [Ag(OH)]+(aq) are reported.

THE CRYSTAL AND MOLECULAR STRUCTURE OF p-NITROPHENACETURIC ACID

Abstract The crystal and molecular structure of p-NO2C6H5CH2CONHCH2COOH or C10 H11 N2O5 has been determined by single crystal x-ray diffraction techniques. The compound crystallizes in the space-group P21. /c with four molecules in a unit cell of dimensions: a = 11.8748(5)Å, b = 11.2732(4)Å, c = 8.8073(5)Å and β = 112.966(4)°. The structure was solved by direct methods and refined to a final value of R = 0.042. The molecule assumes a conformation similar to that found for the analogous side-chain in the penicillin G molecule and hence should be a convenient model system in studying copper catalyzed degradations of penicillin. The hydrogen bonding between the amide oxygen of one molecule to the carboxylic acid proton, 2.67(1)Å, and the amide nitrogen, 2.91(1)A, of another molecule creates a three-dimensional network identical to that found for hippuric acid.

Electron Spin Resonance Study of Liquids during Photolysis: XVII. 3,5-Pyridinedicarboxylic Acid

Radicals present during photolysis of solutions of 3,5-pyridinedicarboxylic acid and its anions have been studied by the ESR method near room temperature. Spectra were analyzed to obtain parameters for four radicals resulting from reduction of the parent compounds. Radicals I, II, and III, respectively, result from hydrogen atom attachment to the nitrogen atom of the parent dicarboxylic acid, its monoanion, and its dianion. Radical IV results from hydrogen atom attachment to one of the carbon atoms bonded to the nitrogen atom of the parent dianion. Conditions and mechanisms of formation are discussed. The pK value for ${\rm I}\rightleftarrows {\rm II}+{\rm H}^{+}$ is about 3.4 and that for ${\rm II}\rightleftarrows {\rm III}+{\rm H}^{+}$ is about 4.3 in aqueous solution. Evidence is given for the switching of the carboxylic acid proton of II between its two equivalent sites.

Alkyl Inductive Effects on Molecular Ionization Potentials. XVI. Esters

Correlation of molecular ionization potentials, E1, with Taft's alkyl inductive substituent constants, σ1(R), has now been extended to include the esters. It is found that three series of esters, the formates, acetates, and methyl alkanoates, fall on three separate straight lines in accord with the general equation E1 = E0 + a1σ1(R), where E0 is the intercept and a1 the slope. The average standard error for the three lines is 0.024 eV with an average correlation coefficient of 0.992, showing that the alkyl substituent exerts an inductive influence on the electron density at the site suffering the electron loss: a lone pair on either the carbonyl or alkoxy oxygen atom. Evidence is deduced for the site of electron expulsion and a prediction is made concerning the site of vapor phase protonation of esters and carboxylic acids. E1 values presently not available experimentally are predicted for several esters.

Protonation of aromatic carboxylic acids in the first excited singlet state

Previous methods for determining the excited state acid-base characteristics of molecules from kinetic data are applicable only to molecules which undergo dissociation upon excitation. This paper presents a method of obtaining kinetic data from fluorescence measurements for compounds, which, upon excitation, take on a proton. The kinetic data so obtained can be used to calculate the excited state acidity constants of the protonated molecules. Comparison, for two naphthoic acids, of the results so obtained with data from the spectral method due to Forster and with data from the pH at which the fluorescence spectrum undergoes a transformation reveals considerable discrepancies: these are discussed briefly.

Synthesis of vitamin b6 derivatives. II. 3‐Hydroxy‐4‐hydroxymethyl‐2‐methyl‐5‐pyridine acetic acid and related substances

AbstractThe syntheses of 3‐hydroxy‐4‐hydroxymethyl‐2‐methyl‐5‐pyridineacetic and ‐5‐pyridine‐propionic acids and several related compounds are described. Although acid hydrolysis of α4,3‐O‐isopropylidene‐5‐pyridoxic acid gives 5‐pyridoxic acid lactone (α‐pyracin), its higher homolog α4,3‐O‐isopropylidene‐pyridoxylformic acid gave a corresponding free alcohol whose carboxylic acid proton was shown to be exchanged rapidly with the 3‐phenolic and ‐4‐alcoholic ‐ protons in nuclear magnetic resonance studies. Inter‐molecular hydrogen bonding between the side chain carboxylic acid and pyridine nitrogen atoms is suggested in the solid state.