Kinetic solvent effects on alkaline decolorization of crystal violet in some aquo-organic solvents

1986 ◽  
Vol 64 (2) ◽  
pp. 300-307 ◽  
Author(s):  
Urmila Mandal ◽  
Sumita Sen ◽  
Kaushik Das ◽  
Kiron Kumar Kundu
Keyword(s):  
Transition State ◽  
Crystal Violet ◽  
Chemical Properties ◽  
Outer Sphere ◽  
Chloride Salt ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Initial State ◽  
Composition Profiles ◽  
Solvent Systems

Rate constants (ks) of alkaline fading of crystal violet (CV+) have been determined at 25 °C by spectrophotometric measurements in aqueous mixtures of some protic, aprotic, and dipolar aprotic cosolvents. Transfer free energies of the substrate (CV+), [Formula: see text], were also determined in some of the solvent systems from solubility measurements of the chloride salt, and by subtracting [Formula: see text] obtained earlier by use of the tetraphenylarsonium tetraphenylboron (TATB) extrathermodynamic assumption. This helped determine transfer free energies of the transition state (X≠), [Formula: see text] values of lyate ion (S−) based on the TATB assumption are already known for all of these solvent systems. The observed log (ks/kw) – composition profiles reveal that the relative solvation of the reacting species rather than the dielectric constant of the solvents dictates the complex variation of the rates of the reaction in these solvent systems. Correlation of [Formula: see text] with [Formula: see text] indicates that the reaction is largely controlled by the relative solvation of S− in most of the cases. But analysis of [Formula: see text] – composition profiles for some of the solvent systems reveals that the non-compensation of the [Formula: see text] contributions of initial-state substrate and of the transition-state complex, which may be considered to be an outer-sphere complex [CV+](S−), is also in accord with what is expected from the relative solvating characteristics of the cosolvents as guided by their respective physico-chemical properties.

Kinetic solvent effects on acid-catalyzed hydrolysis of sucrose in aqueous mixtures of some protic, aprotic, and dipolar aprotic solvents

1986 ◽  
Vol 64 (8) ◽  
pp. 1638-1642 ◽  
Author(s):  
Urmila Mandal ◽  
Kaushik Das ◽  
Kiron Kumar Kundu
Keyword(s):  
Transition State ◽  
Optical Rotation ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Initial State ◽  
Composition Profiles ◽  
Acid Catalyzed ◽  
Solvent Systems ◽  
Hydrolysis Of ◽  
Reference Electrolyte

Rate constants of acid-catalyzed hydrolysis of sucrose (S) to D-glucose and L-fructose have been determined at 25 °C by optical rotation measurements in aqueous mixtures of protophobic protic glycerol (GL), protophilic protic urea (UH), aprotic dioxane (D), and dipolar aprotic dimethyl sulphoxide (DMSO). Transfer free energies of the substrate sucrose, [Formula: see text] have also been determined in the solvents from solubility measurements. These values as well as those of H+, as obtained earlier by use of the widely used tetraphenylarsonium tetraphenylboron (TATB) reference electrolyte assumption, yielded transfer free energies of the transition state. The observed log (ks/kw) – composition profiles reveal that the rates increase monotonically in GL–water mixtures, that decrease more or less monotonically in UH– and DMSO–water mixtures, and decrease up to 10 mol% D in D–water mixtures, beyond which the values tend to increase. Examination of [Formula: see text]–composition profiles for the different species in each case indicates that the initial and transition state solvation get more or less compensated and the observed rates are dictated by the increased solvation of H+ in aqueous UH, DMSO, and D co-solvent systems. But in GL–water mixtures the decreased solvation of the transition state compared with the initial state is overcome by the decreased solvation of H+, thus resulting in the gradual enhancement of the rates of the reaction. The observed linearity of the correlative plots of −δ(ΔG≠) [= RT ln (ks/kw)] vs. [Formula: see text] with distinctly different slopes in the two cases also substantiates the relative importance of H+ solvation in dictating the rates of the reaction in these widely different aqueous co-solvents.

Free energies and entropies of transfer of hydrogen halides from water to aqueous 2-methoxy ethanol and structuredness of the solvents

1985 ◽  
Vol 63 (4) ◽  
pp. 798-803 ◽  
Author(s):  
Prabir K. Guha ◽  
Kiron K. Kundu
Keyword(s):  
Dielectric Constant ◽  
Mixed Solvents ◽  
Three Dimensional ◽  
Halide Ions ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Hydrogen Halides ◽  
Emf Measurements ◽  
Composition Profiles ◽  
The Individual

Standard free energies (ΔGt0) and entropies (ΔSt0) of transfer of HBr and HI from water to some aqueous solutions of 2-methoxy ethanol (ME) have been determined from emf measurements of the cells: Pt, H2 (g, 1 atm)/HBr (m), solvent/AgBr–Ag and Pt, H2 (g, 1 atm)/KOH (m1), KI (m2), solvent/AgI–Ag, respectively, at seven equidistant temperatures ranging from 15 to 45 °C. ΔGt0 values of HBr and HI as well as of HCl obtained from literature, and particularly that of the individual ions obtained by tetraphenylarsonium tetraphenylboron (TATB) assumption, suggest that while H+ is increasingly stabilized by cosolvent-induced larger "basicity", halide ions (X−) are increasingly destabilized by cosolvent-induced decreased "acidity" and the dielectric constant of the mixed solvents compared to that of water. Analysis of the variation of the observed TΔSt0(HX) and particularly of ΔY (= TΔSt0(H+) + TΔS0t.ch (X−), with composition, in the light of Kundu etal's semi-quantitative theory reveals that ME induces breakdown of three dimensional (3D) tetrahedral structures of water at water-rich compositions. This is being followed by an ordered region due to possible H-bonded cosolvent–water complexation and then the usual disordered region due to packing imbalance. Comparison of ΔY(HI)–composition profiles for aqueous mixtures of t-butanol (ButOH), ethylene glycol (EG), and 1,2-dimethoxy ethane (DME) also demonstrates that the remarkable enhancement of 3D water structures by the well known structure promoter ButOH gets succintly diminished when cosolvent ButOH is replaced by EG, ME, and DME, as is expected from structural and electronic considerations of the cosolvents.

Thermodynamics of transfer of glycine, diglycine, and triglycine from water to aqueous solutions of urea, glycerol, and sodium nitrate

1988 ◽  
Vol 66 (3) ◽  
pp. 461-468 ◽  
Author(s):  
Himansu Talukdar ◽  
Sibaprasad Rudra ◽  
Kiron K. Kundu
Keyword(s):  
Sodium Nitrate ◽  
Regular Function ◽  
Scaled Particle Theory ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Thermodynamics Of Transfer ◽  
Different Temperatures ◽  
Composition Profiles ◽  
Cavity Effect ◽  
Nitrate Solutions

Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of glycine (G), diglycine (DG), and triglycine (TG), from water to aqueous mixtures of glycerol (GL) and urea (UH) have been determined from solubility measurements at different temperatures. This was also extended to an ionic cosolvent system like aqueous sodium nitrate solutions for G and DG. The observed [Formula: see text] and [Formula: see text]–composition profiles, as well as those obtained after correcting for the "cavity effect" as estimated by scaled particle theory (SPT), were examined in the light of various interactions. The corrected [Formula: see text]and [Formula: see text] values show a regular function of the peptide chain length of the amino acids and impart useful information regarding the involved relative structural effects of these ionic and non-ionic cosolvents.

The pressure dependence of benzyl chloride solvolysis in aqueous acetone and aqueous dimethylsulfoxide

1970 ◽  
Vol 48 (16) ◽  
pp. 2494-2499 ◽  
Author(s):  
Digby D. Macdonald ◽  
J. B. Hyne
Keyword(s):  
Transition State ◽  
Benzyl Chloride ◽  
Activation Volume ◽  
Aqueous Acetone ◽  
Solvent Composition ◽  
Pressure Data ◽  
Initial State ◽  
First Order ◽  
Solvent Systems ◽  
Aqueous Dimethylsulfoxide

First-order rate constants for the solvolysis of benzyl chloride in a series of aqueous acetone and aqueous dimethylsulfoxide (DMSO) mixtures at 50.100 °C and at various pressures in the range 1–4083 atm are reported. Volume of activation, calculated from the rate/pressure data, is found to exhibit extremum behavior with varying solvent composition in both solvent systems. The activation volumes are dissected into their initial state and transition state contributions by determining the "instantaneous" volumes of solution of benzyl chloride in the solvent systems. The contributions of both the initial state and the transition state to the behavior of the activation volume as a function of solvent composition are discussed.

Determination of absolute transfer free energies of hydroxyl ion from water to aqueous 2-methoxy ethanol

1981 ◽  
Vol 59 (7) ◽  
pp. 1153-1159 ◽  
Author(s):  
Abhijit Bhattacharya ◽  
Asim K. Das ◽  
Kiron K. Kundu
Keyword(s):  
Ethylene Glycol ◽  
Mixed Solvents ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Free Energies Of Transfer ◽  
Hydroxyl Ion ◽  
Relative Stabilization ◽  
Solvent Systems ◽  
Reference Electrolyte

Absolute standard free energies of transfer ΔGt0 of OH− from water to aqueous mixtures of 2-methoxy ethanol (ME) have been evaluated at 298.15 K by combining the apparent transfer free energies of the lyate ion that were obtained from the standard emf's of the double cell:[Formula: see text]and that from the autoionization constants of these mixed solvents determined by use of the cell comprising H2– and Ag–AgCl electrodes. The required ΔGt0 values of K+ and H+ were determined earlier using the well-known tetraphenyl arsonium tetraphenyl boride (TATB) reference electrolyte method. These values and their non-Born type contributions in particular, are found to be increasingly positive in water-rich compositions, indicating that the relative stabilization of OH− and the acidity of the mixed solvents decrease with increasing cosolvent composition. These, when compared with those in aqueous mixtures of ethylene glycol and 1,2-dimethoxy ethane, are found to lie intermediate between the latter solvent systems conforming to what is expected from the structural and electronic features of the cosolvents.

Ion–ion–solvent interactions in aqueous ionic cosolvent systems. IV. Transfer energetics of water, p-nitroaniline, and benzoic acid from emf/solubility measurements at different temperatures in aqueous sodium nitrate solvent system

1988 ◽  
Vol 66 (3) ◽  
pp. 469-475
Author(s):  
Sibaprasad Rudra ◽  
Himansu Talukdar ◽  
Kiron K. Kundu
Keyword(s):  
Benzoic Acid ◽  
Sodium Nitrate ◽  
Solvent System ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Salting Out ◽  
Emf Measurements ◽  
Solvent Interactions ◽  
Different Temperatures ◽  
Composition Profiles

Autoionization constants (Ks) of aqueous mixtures of 1, 2, and 4 m sodium nitrate used as an ionic cosolvent system have been determined from emf measurements of the cell: Pt, H2 (g, 1 atm)/KOH (m1) KCl (m2), solvent/AgCl–Ag at five equidistant temperatures ranging from 15–35 °C. The standard free energies (ΔG0) and entropies (ΔS0) of autoionisation of the solvents were then evaluated from these data. Relative free energies (ΔG0) and entropies of (ΔS0)of autoionization of the solvents when coupled with the previously determined transfer free energies [Formula: see text] and entropies [Formula: see text] of H+ yielded [Formula: see text][Formula: see text],[Formula: see text] and [Formula: see text]. Values of [Formula: see text] and [Formula: see text] obtained after correcting for [Formula: see text], as well as [Formula: see text] and [Formula: see text]obtained after correcting the "cavity effect" and Born-type electrostatic effect suggests that while the "basicity" of the aqueous NaNO3 solutions decreases, the "acidity" more or less increases with NaNO3 concentration. The observed [Formula: see text]– and [Formula: see text]–composition profiles were also examined in the light of Kundu et al.'s four-step transfer process and the involved order–disorder phenomena, respectively, as proposed earlier.Standard free energies [Formula: see text] and entropies [Formula: see text] of transfer of p-nitroaniline (pNA) and benzoic acid (HBz) for the solvent system have also been determined from solubility measurements at different temperatures. The observed [Formula: see text]–and [Formula: see text]–composition profiles appear to reflect the salting-out effect of the salt and the [Formula: see text]–and [Formula: see text]–composition profiles confirm the applicability of either of these quantities rather than [Formula: see text], as a better structural probe both for aquo-ionic and aquo-organic solvents.

Deprotonation and transfer energetics of glycine in aqueous mixtures of urea and glycerol from emf measurements at different temperatures

1989 ◽  
Vol 67 (2) ◽  
pp. 315-320 ◽  
Author(s):  
Himansu Talukdar ◽  
Sibaprasad Rudra ◽  
Kiron K. Kundu
Keyword(s):  
Scaled Particle Theory ◽  
Aqueous Mixtures ◽  
Free Energies ◽  
Emf Measurements ◽  
Transfer Energetics ◽  
Galvanic Cells ◽  
Aqueous Urea ◽  
Different Temperatures ◽  
Composition Profiles ◽  
Reference Electrolyte

Deprotonation constants, Ka(RH2+) and Ka(RH±), of glycine (RH±) have been determined at five equidistant temperatures ranging from 15 to 35 °C by measuring the emf of galvanic cells comprising Pt/H2 and Ag–AgCl electrodes in aqueous mixtures of protophilic protic urea (UH) and protophobic protic glycerol (GL). Medium effects on deprotonation of the acid: [Formula: see text] have been dissected into transfer free energies [Formula: see text] and entropies [Formula: see text] of the species involved as obtained by measuring the transfer energetics [Formula: see text] of RH± from solubility measurements at different temperatures and of H+ based on tetraphenylarsonium tetraphenylborate (TATB) reference electrolyte assumption determined earlier. The [Formula: see text] values obtained after due correction from the cavity effect based on scaled particle theory (SPT) and electrostatic effects including Born and ion–dipole effects for the charged species involved in the two deprotonation equilibria enable better understanding of the solvent effect on the deprotonation constants. Moreover, the [Formula: see text]–composition profiles are found to exhibit similar characteristic maxima and minima as for simple cations and anions in these solvent systems, thus providing useful information on the structural characteristic of these cosolvents. Keywords: deprotonation energetics, glycine, aqueous urea, aqueous glycerol, EMF measurements.

Free energies and entropies of transfer of hydrogen halides from water to aqueous solutions of tetrahydrofuran, dioxane, and 1,2-dimethoxyethane and the structuredness of the solvents

1981 ◽  
Vol 59 (22) ◽  
pp. 3149-3156 ◽  
Author(s):  
Jayati Datta ◽  
Kiron K. Kundu
Keyword(s):  
Aqueous Solutions ◽  
Mixed Solvents ◽  
3D Structure ◽  
Relative Order ◽  
Halide Ions ◽  
Free Energies ◽  
Composition Profiles ◽  
Solvent Systems ◽  
The Individual ◽  
Soft Interactions

Standard free energies (ΔGt0) and entropies (ΔSt0) of transfer of hydrogen iodide from water to some aqueous solutions of tetrahydrofuran (THF), dioxane (D), and 1,2-dimethoxyethane (DME) have been determined by measuring the emf's of the cell: Pt, H2 (g, 1 atm)|KOH (m1), KI (m2), solvent|AgI, Ag at seven equidistant temperatures ranging from 5 to 35 °C. In each of these ethereal solvent systems ΔGt0 values of HI, as well as of HCl and HBr obtained from the literature, and particularly of the individual ions, suggest that while H+ is increasingly stabilized, halide ions are increasingly destabilized due to the influence of cosolvent-induced larger "basicity" and smaller "acidity" of the mixed solvents compared to that of water, and both conformed to the expected order: D < THF < DME. Moreover, the relative order: Cl− > Br− > I− in all the solvent systems is ascribable to the combined effects of "acid–base" and "soft–soft" interactions and the superimposed quadrupolar interactions in the case of D and the charge transfer to solvent (CTTS) complexation effect, especially on I− in the case of THF. Analysis of the entropie contributions, TΔSt0, and particularly of the relative order of ΔY (≡TΔSt0(H+) + TΔSt,ch0(X−)) for X = Cl, Br, and I, in the light of the semi-quantitative theory proposed earlier by Kundu et al., reveals that at initial compositions, while THF promotes 3D structures of water, both D and DME break down the same; at higher compositions all the cosolvents disrupt the structure as usual due to packing imbalance. The nature and relative positions of ΔY–composition profiles also suggest that while increase of hydrophobic groups of the cosolvents increases the stabilization, increase in hydrophilicity or H-bonding sites decreases the stabilization of the 3D structure of water.

Thermodynamics and acoustic effects of quercetin on micellization and interaction behaviour of CTAB in different hydroethanol solvent systems

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Vikrant Abbot ◽  
Poonam Sharma
Keyword(s):  
Pharmaceutical Industry ◽  
Hydrophobic Interactions ◽  
Chemical Properties ◽  
Formulation Development ◽  
Surfactant Interactions ◽  
Physico Chemical ◽  
Ultrasonic Sound ◽  
Apparent Molar Compressibility ◽  
Solvent Systems ◽  
Thermoacoustic Properties

AbstractFlavonoids amongst the class of secondary metabolites possess numerous health benefits, are known for its use in pharmaceutical industry. Quercetin, a flavonoid has more prominent medical advantages however its utilization is constrained because of various instability and insolubility issues and therefore, taken into consideration for studying its physico-chemical properties. In view of that, the thermodynamic and thermoacoustic properties of quercetin were examined in presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at different hydroethanolic concentrations and temperatures. The conductivity studies were used to calculate change in enthalpy (∆Hom), change in entropy (∆Som) and change in Gibbs free Energy (∆Gom) of micellization. The interactions between quercetin and CTAB were found to be endothermic, entropically controlled and spontaneous. Further, ultrasonic sound velocity and density studies were carried out and utilized for the calculation of thermoacoustic parameters i.e. apparent molar volume and apparent molar compressibility. Thermoacoustic properties revealed that at higher surfactant concentration, hydrophobic interactions are dominant. The results suggested that the flavonoid-surfactant interactions in hydroethanolic solutions is more favourable as compared with aqueous solution. Overall, the data is favourable for the framework to be used for detailing advancement, drug development, drug industry, pharmaceutical industry, medical administration and formulation development studies.

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