The H− acidity function for dimethylformamide–water

1970 ◽  
Vol 48 (21) ◽  
pp. 3354-3357 ◽  
Author(s):  
E. Buncel ◽  
E. A. Symons ◽  
Douglas Dolman ◽  
Ross Stewart
Keyword(s):  
Solvent System ◽  
Tetramethylammonium Hydroxide ◽  
Acidity Function ◽  
Hydroxide Ion ◽  
Indicator Method ◽  
Aqueous Dimethylsulfoxide

The H− acidity function has been determined for N,N-dimethylformamide–water mixtures containing tetramethylammonium hydroxide by the Hammett indicator method. Basicity in the aqueous dimethylformamide system exceeds that in aqueous tetramethylenesulfone but is slightly less than in aqueous dimethylsulfoxide, at equivalent molar compositions of solvent and base. However, the basic aqueous dimethylformamide solvent system is only of limited utility as a result of reaction of hydroxide ion with the dimethylformamide.

Strongly basic systems. VIII. The H− function for dimethyl sulfoxide – water – tetramethylammonium hydroxide

1967 ◽  
Vol 45 (9) ◽  
pp. 911-924 ◽  
Author(s):  
Douglas Dolman ◽  
Ross Stewart
Keyword(s):  
Dimethyl Sulfoxide ◽  
Tetramethylammonium Hydroxide ◽  
Strengthening Effect ◽  
Acidity Function ◽  
Substituent Constant ◽  
Substituted Anilines ◽  
Hydroxide Ion ◽  
Substituent Constants ◽  
Hammett Σ Constants ◽  
Increased Activity

An H− acidity function based on the ionization of 24 substituted anilines and diphenylamines has been established in the system dimethyl sulfoxide – water – tetramethylammonium hydroxide. The H− of a 0.011 M solution of tetramethylammonium hydroxide ranges from 12 in water to 26.2 in 99.6 mole % dimethyl sulfoxide – water, an increase in basicity of 14 powers of 10. The increase in basicity is due to the increased activity of the hydroxide ion brought about by the reduction in its solvation in the poor anion-solvating solvent dimethyl sulfoxide, and indicates the extensive solvation enjoyed by the hydroxide ion in water.The pKHA values of the indicator acids vary from 13.9 for 2,4-dinitrodiphenylamine to 25.6 for 3-chloroaniline. From a plot of log KHA versus the Hammett substituent constants (σ) for six monosubstituted diphenylamines, a ρ value of 4.07 is found. Similar results are obtained for the anilines. The acidities of all the substituted diphenylamines do not follow the above-mentioned correlation with the Hammett σ constants; the pKHA values of 4-amino-, 4-methoxy-, 4-methylsulfonyl-, and 4-nitro-diphenylamine are all less than expected from the Hammett σ constants for the substituents in these compounds. The 4-nitro substituent exerts a particularly large acid-strengthening effect on the acidities of aniline and diphenylamine, the decreases in pKHA being approximately 8.4 and 6.8 pK units, respectively. An exalted substituent constant of +1.65 for p-NO2 is needed to account for the acidity of p-nitro-diphenylamine.

The Dissociation of Anilinium Ions in Aqueous Dimethylsulfoxide

1972 ◽  
Vol 50 (4) ◽  
pp. 474-478 ◽  
Author(s):  
Keith Yates ◽  
Graeme Welch
Keyword(s):  
Aqueous Solution ◽  
Solvent System ◽  
Ionization Mechanism ◽  
Normal Order ◽  
Aqueous Dimethylsulfoxide

The pKa values often substituted primary anilines and six substituted tertiary anilines have been determined in 70% DMSO–water. The ΔpKa values relative to those in aqueous solution indicate that DMSO is about 2 log units stronger as a base than H2O. The normal order of basicity (tertiary > primary) is inverted in this solvent system and the Hammett ρ values for the two series provide evidence for a different ionization mechanism than that in water.

STRONGLY BASIC SYSTEMS: III. THE H− FUNCTION FOR VARIOUS SOLVENT SYSTEMS

1964 ◽  
Vol 42 (7) ◽  
pp. 1681-1693 ◽  
Author(s):  
Ross Stewart ◽  
J. P. O'Donnell
Keyword(s):  
Lithium Hydroxide ◽  
Dimethyl Sulphoxide ◽  
Tetramethylammonium Hydroxide ◽  
Acidity Function ◽  
Function Concept ◽  
Substituted Anilines ◽  
Hammett Acidity Function ◽  
Solvent Systems

The Hammett acidity function concept has been used to determine simultaneously the pKa values of 24 substituted anilines and diphenylamines and the H− values of various solvent systems. The following solvent systems were examined (the most basic H− value obtained for each is shown in parentheses): water containing benzyltrimethylammonium hydroxide (16.20); pyridine–water containing tetramethylammonium hydroxide (18.91); sulpholane–water containing tetramethylammonium hydroxide (19.18); dimethyl sulphoxide–water containing tetramethylammonium hydroxide (18.61); water containing lithium hydroxide (14.31).In addition to these results adjustments have been made to previously published scales for hydrazine–water (15.08) and ethylenediamine–water (15.48).

Meisenheimer Complex Formation Between 1,3,5-Trinitrobenzene and Hydroxide Ion. Equilibrium Constants for the Dimethylformamide–Water Solvent System

1972 ◽  
Vol 50 (11) ◽  
pp. 1729-1733 ◽  
Author(s):  
E. A. Symons ◽  
E. Buncel
Keyword(s):  
Complex Formation ◽  
Aqueous Medium ◽  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Solvent System ◽  
Medium Composition ◽  
Hydroxide Ion ◽  
Spectrophotometric Methods ◽  
Water Solvent ◽  
Sigma Complex

Sigma-complex formation between 1,3,5-trinitrobenzene (TNB) and hydroxide ion has been studied quantitatively as a function of medium composition for part of the dimethylformamide (DMF)–water solvent system by spectrophotometric methods. Only a 1:1 complex is detected under the conditions of measurement, with [TNB] ≥ [OH−]. The equilibrium constant (Keq) for complex formation in 22 mol % DMF has the value 3 × 10−3 l mol−1, compared with 3 l mol−1 in purely aqueous medium. Further increases in Kcq occur as the DMF content of the medium is raised; in 50 mol % DMF Keq ≈ 105, but reliable Keq values could not be obtained in this region of medium composition. The increase in Keq with increasing DMF content is interpreted largely on the basis of hydroxide ion desolvation.

1,3-Dinitrobenzene – hydroxide ion interactions. Equilibrium constants for σ-complex formation in the dimethylformamide–water solvent system

1981 ◽  
Vol 59 (22) ◽  
pp. 3168-3176 ◽  
Author(s):  
Erwin Buncel ◽  
Allen W. Zabel
Keyword(s):  
Equilibrium Constants ◽  
Solvent System ◽  
Medium Composition ◽  
Hydroxide Ion ◽  
Interacting Species ◽  
Ion Interactions ◽  
Water Solvent ◽  
Constant Measurement ◽  
Uv Visible ◽  
Solvent Isotope

The results of a uv–visible spectroscopic study of the interaction of 1,3-dinitrobenzene (DNB) with hydroxide ion in aqueous dimethylformamide (DMF) media are reported. Formation of several spectral species has been discerned, depending on factors such as the relative concentrations of the reactants, the time scale of the experiments, and the medium composition. The principal interaction is formation of the 1-hydroxy-2,4-dinitrocyclohexadienate anion. The molar absorptivities of this σ-complex, and the equilibrium constants (Ke) for its formation, have been determined as a function of medium composition. Values of Ke increase from 7.5 M−1 to 3 × 105M−1 as the DMF content of the medium is changed from 57.4 to 95.8 mol% DMF. A solvent isotope effect, Ke(D2O)/Ke(H2O), of ca. 0.4 has been observed. Structural and medium effects in this and related systems are evaluated. Correlations between log Ke and H− are examined using the stoichiometric as well as the calculated free hydroxide ion concentrations. Attention is drawn to an important condition for equilibrium constant measurement in systems where one of the interacting species contributes significantly to the overall basicity, or to another property of the medium.

IONIZATION OF ORGANIC COMPOUNDS: II. THIOACETAMIDE IN AQUEOUS SODIUM HYDROXIDE. THE H− ACIDITY FUNCTION

1962 ◽  
Vol 40 (3) ◽  
pp. 399-407 ◽  
Author(s):  
J. T. Edward ◽  
I. C. Wang
Keyword(s):  
Sodium Hydroxide ◽  
Organic Compounds ◽  
Aqueous Sodium Hydroxide ◽  
Ion Concentration ◽  
Acidity Function ◽  
Concentrated Solutions ◽  
Salting Out ◽  
Hydroxide Ion ◽  
Aqueous Sodium ◽  
Ionization Ratio

The ionization ratio of thioacetamide in aqueous sodium hydroxide, determined spectrophotometrically, is proportional to the concentration of hydroxide ion up to a concentration of about 1 M, and indicates a pKHA of 13.4. For more concentrated solutions the ionizing power increases more rapidly than the hydroxide ion concentration; from the experimentally determined ionization ratios the values of the h− acidity function for 1–6 M sodium hydroxide have been calculated. The relation of h− values to the salting-out parameters and water activities of concentrated sodium hydroxide solutions is discussed.

Kinetics and mechanism of hydrolysis of 3-diazobenzofuran-2-one and its hydrolysis product (3-hydroxybenzofuran-2-one)

2002 ◽  
Vol 80 (1) ◽  
pp. 82-88
Author(s):  
Y Chiang ◽  
A J Kresge ◽  
Q Meng
Keyword(s):  
Acid Catalysis ◽  
Hydrolysis Product ◽  
Diazo Compound ◽  
Acidity Function ◽  
Hydroxide Ion ◽  
Mechanism Of Hydrolysis ◽  
Acid Catalyzed ◽  
Catalyzed Reactions ◽  
Rate Profile ◽  
Hydrolysis Of

Rates of acid-catalyzed hydrolysis of 3-diazobenzofuran-2-one, measured in concentrated aqueous perchloric acid and hydrochloric acid solutions, were found to correlate well with the Cox–Yates Xo excess acidity function, giving kH+ = 1.66 × 10–4 M–1 s–1, m‡ = 0.86 and kH+ /kD+ = 2.04. The normal direction (kH/kD > 1) of this isotope effect indicates that hydrolysis occurs by rate-determining protonation of the substrate on its diazo-carbon atom. It was found previously that the next higher homolog of the present substrate, 4-diazoisochroman-3-one, also undergoes hydrolysis by this reaction mechanism but with a rate constant 15 times greater than that for the present substrate; this difference in reactivity can be understood in terms of the various resonance forms that contribute to the structures of these substrates. The product of the present hydrolysis reaction is 3-hydroxybenzofuran-2-one, which itself quickly undergoes subsequent acid-catalyzed hydrolysis to 2-hydroxymandelic acid. The acidity dependence of this subsequent hydrolysis is much shallower than that of the diazo compound precursor, and rates of reaction correlate as well with [H+] as with Xo. This is due in part to incursion of a nonproductive protonation on the hydroxy group of 3-hydroxy benzo furan-2-one that impedes hydrolysis and produces saturation of acid catalysis. Rates of hydrolysis of the hydroxy compound were also measured in dilute HClO4 and NaOH solutions as well as in CH3CO2H, H2PO4–, (CH2OH)3CNH3+, and NH4+ buffers, and the rate profile constructed from these data showed the presence of uncatalyzed and hydroxide ion-catalyzed reactions. This hydroxide-ion catalysis became saturated at [NaOH] [Formula: see text] 0.05 M, implying occurrence of yet another nonproductive substrate ionization. Key words: diazo compound hydrolysis, lactone hydrolysis, Cox–Yates excess acidity, acid catalysis, alcohol protonation.

An acidity function in ethanol – sulfuric acid based on the protonation of diphenylamines

1967 ◽  
Vol 45 (9) ◽  
pp. 903-910 ◽  
Author(s):  
Douglas Dolman ◽  
Ross Stewart
Keyword(s):  
Sulfuric Acid ◽  
Nitro Group ◽  
Strong Interaction ◽  
Acidic Solution ◽  
Sulfuric Acid Concentration ◽  
Substituent Effects ◽  
Solvent System ◽  
Acidity Function ◽  
Substituent Constants ◽  
Hammett Σ Constants

A Hammett H0 acidity function based on the protonation of 17 diphenylamines in 20 volume % ethanol – aqueous sulfuric acid has been established. The H0 value for the most acidic solution studied (11.2 M sulfuric acid) is −6.97. This acidity function differs from that based on the protonation of azobenzenes in the same solvent system; the latter diverges to more negative H0 values as the sulfuric acid concentration increases.The [Formula: see text] values for the protonation of the diphenylamines vary from +1.36 for 4-methoxy-diphenylamine to − 6.21 for 4,4′-dinitrodiphenylamine. A plot of [Formula: see text] versus the Hammett σ constants for five monosubstituted diphenylamines yields a ρ value of +3.36. The [Formula: see text] values for 4-methoxy-, 4-methyl-, 4-methylsulfonyl-, and 4-nitro-diphenylamine are all less (more negative) than expected from the Hammett substituent constants. The substituent effects on the basicities of aniline and diphenylamine are the same.The basicities of several nitro-substituted diphenylamines appear to vary regularly, and do not reflect the presence of a strong interaction between the nitro group and sulfuric acid.

scholarly journals The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids

Molecules ◽  
2020 ◽  
Vol 26 (1) ◽  
pp. 62
Author(s):  
Ting He ◽  
Cheng-Bin Hong ◽  
Peng-Chong Jiao ◽  
Heng Xiang ◽  
Yan Zhang ◽  
...  
Keyword(s):  
Ionic Liquids ◽  
Amino Acid ◽  
Acid Ester ◽  
Amino Acid Ester ◽  
Acidity Function ◽  
Brønsted Acidity ◽  
Protic Ionic Liquids ◽  
Indicator Method ◽  
Pka Values ◽  
Brönsted Acidity

[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (pKa) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The pKa values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (H0) values (0.05 mol·L−1) were about 4.6 in water. In addition, the pKa values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.

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