Acid Ionizations of Nitroalkanes in Aqueous Solution

Calorimetric measurements have led to ΔH0 values for ionization of nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane in aqueous solution at 298°K. Combinations of these enthalpies with free energies from equilibrium constants for ionization have led to ΔS0 values for the ionization reactions. It is noted that the trend toward decreasing pK with methyl substitution in nitroalkanes is unusual compared to phenols and carboxylic acids. Similarly, correlations of ΔS0 with ΔG0 and ΔH0 are different for nitroalkanes than for other acids.

Download Full-text

Carbonyl Addition Reactions: Factors Affecting the Hydrate–Hemiacetal and Hemiacetal–Acetal Equilibrium Constants

Canadian Journal of Chemistry ◽

10.1139/v75-125 ◽

1975 ◽

Vol 53 (6) ◽

pp. 898-906 ◽

Cited By ~ 117

Author(s):

J. Peter Guthrie

Keyword(s):

Aqueous Solution ◽

Carbonyl Compounds ◽

Equilibrium Constants ◽

Substituent Effects ◽

Steric Effects ◽

Addition Reactions ◽

Free Energies ◽

Electronic Effects ◽

Factors Affecting ◽

Analogous Formula

Equilibrium constants for hydrate–hemiacetal interconversion in aqueous solution at 25° have been measured for four fluorinated carbonyl compounds: compound, alcohol, K4 (M−1): CF3CHO, C2H5OH, 2.3; CF3COCH3, CH3OH, 1.0; CF3COPh, CH3OH, 3.5; CF3COCF3, CH3OH, 0.14. These values, combined with values from the literature, permit an examination of substituent effects upon the equilibrium constant for[Formula: see text]The free energy change for this process, corrected for symmetry and steric effects, follows the equation[Formula: see text]Thus electronic effects upon this equilibrium are generally small and in fact are often smaller than steric effects.This analysis permits and justifies the calculation of free energies of formation of [Formula: see text] compounds from the (more generally measurable) free energies of formation of the analogous [Formula: see text] compounds.

Download Full-text

Influence of the Solvation Upon the Reaction of α-Cyclodextrin with Carboxylic Acids, Their Methyl Esters, and Their Sodium Salts in Aqueous Solution Studied by Calorimetric Measurements

Journal of Solution Chemistry ◽

10.1007/s10953-005-4498-x ◽

2005 ◽

Vol 34 (6) ◽

pp. 731-737 ◽

Cited By ~ 6

Author(s):

Hans-Jürgen Buschmann ◽

Eckhard Schollmeyer

Keyword(s):

Aqueous Solution ◽

Carboxylic Acids ◽

Methyl Esters ◽

Sodium Salts ◽

Calorimetric Measurements

Download Full-text

Calorimetric investigations of Al3+(aq), Al(OH)4−(aq), and aluminium–citrate complexes at 298.15 K

Canadian Journal of Chemistry ◽

10.1139/v97-132 ◽

1997 ◽

Vol 75 (8) ◽

pp. 1110-1113 ◽

Cited By ~ 3

Author(s):

Ching-hsien Wu ◽

Celina Dobrogowska ◽

Xin Zhang ◽

Loren G. Hepler

Keyword(s):

Aqueous Solution ◽

Aluminum Hydroxide ◽

Equilibrium Constants ◽

A Value ◽

Calorimetric Measurements ◽

Aluminum Complexes ◽

Aluminium Citrate ◽

Calorimetric Investigations ◽

Citrate Ions

We have combined results of earlier measurements leading to equilibrium constants for formation and reaction of aluminum–citrate complexes in aqueous solution at 298.15 K with results of our calorimetric measurements at this same temperature to obtain ΔH values for reactions of Al3+(aq) with citrate ions. Results of some of these calorimetric measurements also lead to a value of ΔH for the reaction Al3+(aq) + 4 OH`(aq) = Al(OH)4−(aq). Keywords: aluminum hydroxide, Al(OH)4−(aq), thermodynamics; aluminium–citrate complexes, thermodynamics; citrate–aluminum complexes, thermodynamics; aluminum (3+, aq), thermodynamics.

Download Full-text

Equilibrium Study on Reactive Extraction of Lactic Acid with Tri-n – Butyl Phosphate in n - Hexane

ASEAN Journal of Chemical Engineering ◽

10.22146/ajche.49737 ◽

2013 ◽

Vol 12 (2) ◽

pp. 1

Author(s):

Panut Mulyono ◽

Anita Pardah

Keyword(s):

Aqueous Solution ◽

Lactic Acid ◽

Ambient Temperature ◽

Carboxylic Acids ◽

Distribution Ratio ◽

Equilibrium Constants ◽

Reactive Extraction ◽

Extraction Temperature ◽

Process Selection ◽

Initial Concentration

Extraction of carboxylic acids from dilute aqueous solution using traditional solvents such as ketones, alcohols, ethers, and ester is inefficient because the distribution ratio is rather low. Reactive extraction which exploits reversible chemical complexation is an effective separation process for extraction of carboxylic acids from aqueous streams such as fermentation broths and wastewaters. In the extraction process, selection of the solvent is an important aspect to be considered. Considering its solubility in water, cost and availability, tri-n-butyl phosphate (TBP) seems to be an attractive solvent for the extraction of lactic acid from aqueous solution. The purpose of this experiment is to study the equilibrium of the reactive extraction of lactic acid in aqueous solution with TBP in n-hexane. The parameters studied in this experiment were initial concentration of lactic acid in the aqueous phase, TBP concentration in n-hexane phase, and the extraction temperature. The experiments at ambient temperature were carried out using a separatory funnel, while the experiments at other than ambient temperature were carried out using erlenmeyer flask and water bath shaker to adjust the temperature. In this experiment, the initial concentration of lactic acid was varied from 0.1 to 0.5 gmol/dm3. The range of initial TBP concentrations in n-hexane was 0.1 to 1.0 gmol/dm3 and the extraction temperature range was 283 to 313 K. The experimental results showed that the higher the initial concentration of lactic acid in aqueous solution, the higher the distribution ratio for a fixed TBP concentration and extraction temperature. For a fixed initial concentration of lactic acid in aqueous solution and extraction temperature, the distribution ratio of lactic acid is increased by increasing TBP concentration. The overall equilibrium constants (Kpq) for the experiments using TBP concentration ranging from 0.1 to 1.0 gmol/dm3 at the extraction temperature of 293 K are calculated to be 0.0668 to 0.5144. Kpq for the experiments at the temperature ranging from 283 to 313 K at the initial concentration of lactic acid of 0.2 gmol/L are found to be 0.0122 to 0.8856. The Kpq as a function of temperature (T) in K can be expressed as ln Kpq = 10,596/T - 38.08 with sum of square of error of 0.14.

Download Full-text

Tautomerization equilibria for phosphorous acid and its ethyl esters, free energies of formation of phosphorous and phosphonic acids and their ethyl esters, and pKa values for ionization of the P—H bond in phosphonic acid and phosphonic esters

Canadian Journal of Chemistry ◽

10.1139/v79-039 ◽

1979 ◽

Vol 57 (2) ◽

pp. 236-239 ◽

Cited By ~ 81

Author(s):

J. Peter Guthrie

Keyword(s):

Aqueous Solution ◽

Free Energy ◽

Equilibrium Constants ◽

Phosphorous Acid ◽

Triethyl Phosphite ◽

Ethyl Esters ◽

Free Energies ◽

Phosphonic Acids ◽

Hydroxy Compounds ◽

Energy Relations

From data in the literature the free energies of formation in aqueous solution of triethyl phosphite and diethyl phosphonate can be calculated as −138.4 ± 1.7 and −165.1 ± 2.0 kcal mol−1, respectively. From these values, by application of free energy relations which we have published, the free energies of formation of the corresponding hydroxy compounds can be calculated and thence the equilibrium constants for tautomerization, which are 107.2, 108.7, and 1010.3 in favor of the tetracoordinate phosphonate tautomer for P(OEt)2OH, P(OEt)(OH)2, and P(OH)3, respectively. Using estimated pKa values for the tricoordinate phosphite species the tautomerization equilibria for the anions could also be calculated, as could the pKa values from the P—H bonds: 13, 26, and 38 for H—PO(OEt)2, H—PO2(OEt)−, and H—PO32−, respectively.

Download Full-text

Effect of the acyl substituent on the equilibrium constant for hydration of esters

Canadian Journal of Chemistry ◽

10.1139/v80-201 ◽

1980 ◽

Vol 58 (13) ◽

pp. 1281-1294 ◽

Cited By ~ 38

Author(s):

J. Peter Guthrie ◽

Patricia A. Cullimore

Keyword(s):

Aqueous Solution ◽

Equilibrium Constant ◽

Rate Constant ◽

Rate Constants ◽

Acid Catalysis ◽

Methyl Esters ◽

Equilibrium Constants ◽

Free Energies ◽

General Acid ◽

Aldehydes And Ketones

Heats of hydrolysis have been measured for the trimethyl orthoesters of isobutyric, propionic, benzoic, methoxyacetic, chloroacetic, and cyanoacetic acids using aqueous acid with an organic cosolvent where necessary, and of the corresponding esters in alkaline solution. Solubilities or free energies of transfer from gas to aqueous solution have been measured, permitting calculation of the free energies of formation of the aqueous orthoesters, and by methods which we have published previously, calculation of the free energies of formation of the covalent hydrates of the esters, and the free energy changes for hydration of these esters.Using estimated pKa values equilibrium constants were calculated for the addition of hydroxide to the esters. The data are in good agreement with the appropriate Marcus equation relating rate and equilibrium constants with a value for b of 8.99 ± 0.17. This line was used to estimate the equilibrium constant for addition of hydroxide, and thence of water, to some additional esters where only the rate constant was available. Rate constants for hydrolysis of methyl esters in aqueous solution at 25 °C were calculated from literature data, correcting for the effect of other conditions as necessary. From the equilibrium constants for addition of water we could estimate the rate constants for uncatalyzed hydrolysis; for the cases where this rate constant has been measured, the agreement was satisfactory. For acid catalyzed hydrolysis the data permit a test of the two alternative mechanisms considered previously, namely specific acid catalysis and general acid catalysis with hydronium ion acting as a general acid. For esters the mechanism is clearly specific acid catalysis, but for aldehydes and ketones it appears very likely that the mechanism is general acid catalysis.

Download Full-text

2-Deoxyribose Radicals in the Gas Phase and Aqueous Solution. Transient Intermediates of Hydrogen Atom Abstraction from 2-Deoxyribofuranose

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc20051769 ◽

2005 ◽

Vol 70 (11) ◽

pp. 1769-1786 ◽

Cited By ~ 4

Author(s):

Luc A. Vannier ◽

Chunxiang Yao ◽

František Tureček

Keyword(s):

Aqueous Solution ◽

Hydrogen Atom ◽

Gas Phase ◽

Computational Study ◽

Hydrogen Atom Abstraction ◽

Oh Radical ◽

Free Energies ◽

Intramolecular Hydrogen ◽

Solvation Free Energies ◽

Transient Intermediates

A computational study at correlated levels of theory is reported to address the structures and energetics of transient radicals produced by hydrogen atom abstraction from C-1, C-2, C-3, C-4, C-5, O-1, O-3, and O-5 positions in 2-deoxyribofuranose in the gas phase and in aqueous solution. In general, the carbon-centered radicals are found to be thermodynamically and kinetically more stable than the oxygen-centered ones. The most stable gas-phase radical, 2-deoxyribofuranos-5-yl (5), is produced by H-atom abstraction from C-5 and stabilized by an intramolecular hydrogen bond between the O-5 hydroxy group and O-1. The order of radical stabilities is altered in aqueous solution due to different solvation free energies. These prefer conformers that lack intramolecular hydrogen bonds and expose O-H bonds to the solvent. Carbon-centered deoxyribose radicals can undergo competitive dissociations by loss of H atoms, OH radical, or by ring cleavages that all require threshold dissociation or transition state energies >100 kJ mol-1. This points to largely non-specific dissociations of 2-deoxyribose radicals when produced by exothermic hydrogen atom abstraction from the saccharide molecule. Oxygen-centered 2-deoxyribose radicals show only marginal thermodynamic and kinetic stability and are expected to readily fragment upon formation.

Download Full-text