Thermodynamics of Transfer of Organic Molecules from Water to Acid Solutions. The Effects of Nitro Substitution

The free energies, enthalpies, and entropies of transfer for a series of neutral aromatic solutes from water to aqueous sulfuric and perchloric acids have been determined by measuring the "medium effect" activity coefficient over a range of temperatures. The more negative free energies of transfer (salting-in) into perchloric acid relative to sulfuric acid are due to more favorable entropy terms, although enthalpies of transfer to perchloric acid solutions are similar to or more positive than those for sulfuric acid solutions. The generally observed salting-in caused by substitution of a nitro group in a neutral solute (the nitro-group effect) results from a more favorable enthalpy of transfer, with a small amount of compensation from the entropy term. A brief discussion of the solute–solvent interactions responsible for these observations is presented.

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Protonation acidity constants for benzotoluidides in sulfuric acid solutions

Open Chemistry ◽

10.1007/s11532-005-0004-y ◽

2006 ◽

Vol 4 (1) ◽

pp. 56-67 ◽

Cited By ~ 2

Author(s):

Goran Stojković ◽

Frosa Anastasova

Keyword(s):

Sulfuric Acid ◽

Dissociation Constants ◽

Uv Spectroscopy ◽

Principal Component ◽

Medium Effect ◽

Acid Solutions ◽

Acidity Constants ◽

Protonation Reaction ◽

Conjugate Acid ◽

Sulfuric Acid Solutions

AbstractThe protonation of o-, m-and p-benzotoluidide in sulfuric acid solutions is studied by UV spectroscopy in the 190–350 nm region. Principal component analysis is applied to estimate the contributions of the effect of protonation and the medium effect. For the substances studied in this work, the first principal component (PC) captures about 98 % of the variance and the second PC ∼100 % of the cumulative percentage variance in the 210–350 nm region. The same spectral region is used for calculation of the ionization ratio from the coefficients of the first PC and mole fractions of the base and its conjugate acid. Using these data and Hammett's equation (pK BH + = H X + log I), the pK BH + values for the protonation reaction are obtained. The dissociation constants as well as the solvent parameters m* (∼0.43) and ϕ (∼0.60) are calculated using the Excess Acidity Method (-pK BH += 2.28–2.30) and the Bunnett-Olsen Method (-pK BH += 2.24–2.28). The probable sites of protonation are discussed.

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The ketonization of acetophenone enol in concentrated aqueous sulphuric and perchloric acid solutions. Implication on X acidity function correlations of the enolization reaction and determination of the keto–enol equilibrium constant as a function of acidity

Canadian Journal of Chemistry ◽

10.1139/v90-257 ◽

1990 ◽

Vol 68 (10) ◽

pp. 1653-1656 ◽

Cited By ~ 4

Author(s):

Y. Chiang ◽

A. J. Kresge ◽

R. A. More O'ferrall ◽

B. A. Murray ◽

N. P. Schepp ◽

...

Keyword(s):

Sulfuric Acid ◽

Key Words ◽

Equilibrium Constant ◽

Perchloric Acid ◽

Acidity Function ◽

Acid Solutions ◽

Function Correlation ◽

Aqueous Perchloric Acid ◽

Sulfuric Acid Solutions

Rates of ketonization of the enol of acetophenone, generated by flash photolytic photohydration of phenylacetylene, were measured in aqueous sulfuric and perchloric acid solutions over the concentration range 1–50 wt.% acid; rates of enolization of acetophenone, monitored by bromine scavenging, were also measured in aqueous perchloric acid solutions over the same concentration range. The results suggest that the curvature observed in a previous X acidity function correlation of the rate of enolization in sulfuric acid solutions was an artifact produced by insufficiently efficient scavenging, and that introduction of the activity of water in the correlating expression, used previously to eliminate the curvature and believed to reflect covalent involvement of water in the enolization reaction, is unnecessary. The present results also show that the keto–enol equilibrium constant for acetophenone decreases with increasing acidity in these concentrated sulfuric and perchloric acid solutions. Key words: acetophenone, enolization, ketonization, keto–enol equilibrium, concentrated acid solutions.

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Determination and structural correlation of pK BH + for meta- and para- substituted benzamides in sulfuric acid solutions

Journal of the Serbian Chemical Society ◽

10.2298/jsc0610061s ◽

2006 ◽

Vol 71 (10) ◽

pp. 1061-1071 ◽

Cited By ~ 1

Author(s):

Goran Stojkovic ◽

Emil Popovski

Keyword(s):

Sulfuric Acid ◽

Dissociation Constants ◽

Uv Spectroscopy ◽

Principal Component ◽

Medium Effect ◽

Acid Solutions ◽

Structural Correlation ◽

Total Variability ◽

Substituted Benzamides ◽

Sulfuric Acid Solutions

The protonation of some meta and para substituted benzamides in sulfuric acid solutions was studied by UV spectroscopy in the 190-350 nm region. Principal component analysis was applied to separate the effect of protonation from the medium effect. The spectral region 200-350nm was used for the calculation of the ionization ratio from coefficient of the first principal component, which explains about 95-98% of the total variability. The dissociation constants as well as the solvation parameters m* and ? were calculated using the excess acidity method and the Bunnett-Olsen method. The pK BH + values obtained with the H A function (defined by the average m* - values) are in satisfactory agreement with those calculated with the previously mentioned methods. The pK BH + values were correlated with structure using the Hammett (?=-0.91) and Taft approach. It was found that the inductive effect is more relevant than the resonance one for both substituted benzamides (meta and para). .

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