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.

Hydrogen exchange studies. XIV. Kinetics and mechanism of base-catalyzed hydrogen exchange in 1,3-dinitrobenzene in aqueous dimethylformamide and relationship with σ-complex formation

1981 ◽  
Vol 59 (22) ◽  
pp. 3177-3187 ◽  
Author(s):  
Erwin Buncel ◽  
Allen W. Zabel
Keyword(s):  
Complex Formation ◽  
Rate Constants ◽  
Hydrogen Exchange ◽  
Equilibrium Constants ◽  
Medium Composition ◽  
Proton Exchange ◽  
Ion Concentrations ◽  
First Order ◽  
Order Rate ◽  
Insight Into

Kinetic data have been evaluated for hydrogen exchange in 1,3-dinitrobenzene (DNB), occurring at the 2-position, in dimethylformamide (DMF) – D2O mixtures containing deuteroxide ion. The pseudo first order rate constants for exchange, kobs, show inverse dependence on the initial DNB concentration, which can be quantitatively related to the extent of σ-complex formation in these systems. The profile for kobs as function of medium composition exhibits a maximum at ca. 70 mol% DMF, and εapp for σ-complex formation reaches a plateau at about the same medium composition. The equilibrium constants for σ-complex formation, Ke, are used to calculate the free, or uncomplexed, deuteroxide ion concentrations, which then allow one to calculate k2, the second order rate constants for exchange. The k2 values show a uniformly increasing tendency with increased DMF content. Correlations with medium basicity are examined, and the nature of the log k2 and log Ke vs. H− plots afford insight into the origin of the medium dependence of proton exchange. The results of the present study are consistent with the σ-complex being an unreactive form of the substrate towards exchange, which occurs via uncomplexed DNB present in small concentration. The study also rules out the possibility that the colored species present in these systems is the carbanion formed on deprotonation of DNB.

Factor analysis as a complement to band resolution techniques. VI. Complex formation between pentachlorophenol-OD and acetone

1979 ◽  
Vol 57 (20) ◽  
pp. 2707-2713 ◽  
Author(s):  
J. Korppi-Tommola ◽  
H. F. Shurvell
Keyword(s):  
Principal Component Analysis ◽  
Factor Analysis ◽  
Complex Formation ◽  
Equilibrium Constant ◽  
Isotope Effect ◽  
Infrared Spectra ◽  
Equilibrium Constants ◽  
Principal Component ◽  
Proton Donor ◽  
Good Agreement

Complex formation between pentachlorophenol-OD (PCP-OD) and acetone and acetone-d6 in CCl4 solution has been studied. Digitized infrared spectra in the O—D stretching region ν(OD) of PCP-OD and the C—O stretching region ν(CO) of acetone have been recorded from solutions of various concentrations. The present results are compared with previous work on complex formation between PCP and the same acceptor molecules. In the ν(OD) region, factor analysis (principal component analysis) and a concentration study of the areas of the resolved band components suggest that two (1:1) complexes occur in solution. The equilibrium constant obtained for one of the complexes shows an isotope effect due to deuteration of the proton donor. In the ν(CO) region, only one band due to complexed species was resolved. Equilibrium constants calculated using the results from the ν(OD) and ν(CO) regions are in good agreement with each other.

Kinetics and mechanisms of the reaction of 2,4,6-trinitrocumene and 2,4,6-trinitroethylbenzene with 1,1,3,3-tetramethylguanidine in N,N-dimethylformamide solvent

1987 ◽  
Vol 65 (5) ◽  
pp. 1007-1011 ◽  
Author(s):  
Mihir K. Biswas ◽  
Arnold Jarczewski ◽  
Kenneth T. Leffek
Keyword(s):  
Carbon Atom ◽  
Complex Formation ◽  
Proton Transfer ◽  
Equilibrium Constant ◽  
Rate Constants ◽  
Equilibrium Constants ◽  
Activation Parameters ◽  
Reaction Parameters ◽  
Deuterium Isotope Effect ◽  
Constant Rate

The reaction of tetramethylguanidine (TMG) with trinitrocumene (TNC) and trinitroethylbenzene (TNEB) in dimethylformamide solvent has been studied with respect to products and kinetics. For TNC only σ-complex formation with the benzene ring was observed, for which the equilibrium constant, rate constants, and activation parameters were measured. For TNEB, both σ-complex formation and proton transfer from the σ-carbon atom of the ethyl group were observed. The equilibrium constants, rate constants, and activation parameters were separately determined for each reaction and a primary deuterium isotope effect, kH/kD = 13.6 (at 20 °C), was found for the proton transfer. The reaction parameters are compared to those for proton transfer from TNT to tetramethylguanidine in DMF solvent.

Equilibrium constants for σ-complex formation between cyanide ion and 1,3,5-trinitrobenzene in alcoholic solvents

1969 ◽  
Vol 47 (22) ◽  
pp. 4129-4133 ◽  
Author(s):  
E. Buncel ◽  
A. R. Norris ◽  
W. Proudlock ◽  
K. E. Russell
Keyword(s):  
Complex Formation ◽  
Equilibrium Constant ◽  
Equilibrium Constants ◽  
Primary Factor ◽  
Aprotic Solvents ◽  
Kcal Mole ◽  
Cyanide Ion ◽  
Direct Calorimetry ◽  
Entropy Changes ◽  
Enthalpy Changes

Equilibrium constants have been determined spectrophotometrically for the reaction of cyanide ion with 1,3,5-trinitrobenzene in methanol, ethanol, n- and iso-propanol, and n- and t-butanol. The equilibrium constants at 25 °C vary from 39 1 mole−1 for the reaction in methanol to 500 000 1 mole−1 with t-butanol as solvent. Enthalpy changes, determined from equilibrium measurements and by direct calorimetry, vary from 0 to −15.5 kcal mole−1 and the calculated entropy changes decrease from 7 to −26 cal deg−1mole−1 as the solvent is changed from methanol to t-butanol. These results are interpreted on the basis that desolvation of the small cyanide ion is the primary factor influencing enthalpies and entropies of reaction. The equilibrium constant in t-butanol is comparable to the values observed for aprotic solvents such as chloroform and acetone.

Conversion of glucose into furans in the presence of AlCl3 in an ethanol–water solvent system

2012 ◽  
Vol 116 ◽  
pp. 190-194 ◽  
Author(s):  
Yu Yang ◽  
Changwei Hu ◽  
Mahdi M. Abu-Omar
Keyword(s):  
Solvent System ◽  
Water Solvent

Effect of Cellulose Coating on Properties of Cotton Fabric

2016 ◽  
Vol 860 ◽  
pp. 81-84
Author(s):  
Bandu Madhukar Kale ◽  
Jakub Wiener ◽  
Jiri Militky ◽  
Hafiz Shahzad Maqsood
Keyword(s):  
Tensile Strength ◽  
Cotton Fabric ◽  
Solvent System ◽  
Dissolving Pulp ◽  
Cotton Fibers ◽  
Cellulose Solution ◽  
Dyeing Properties ◽  
Sem Micrographs ◽  
Coated Substrate ◽  
Water Solvent

Cellulose solution was used for coating and it was prepared by dissolving pulp cellulose in Urea-Thiourea-NaOH-Water solvent system. Reactive Red 240 dye was used for dyeing the coated as well as control cotton fabric. The effect of cellulose coating on the dyeing properties of cotton fabric was studied by measuring K/S values of the coated substrate at various concentrations of cellulose and dye. K/S value decreased after coating cellulose on the surface of cotton fabric. The lightness of cotton fabric increased after cellulose coating. SEM micrographs revealed that coated cellulose was attached to cotton fibers. Tensile strength increased after cellulose coating.

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