1622-95-3Relevant articles and documents
Preferential Solvation of a Dipolar Solute in Mixed Binary Solvent. A Study by UV-Visible Spectroscopy
Chatterjee, P.,Bagchi, S.
, p. 3311 - 3314 (1991)
The preferential solvation in mixed binary solvent, e.g., ethanol + acetonitrile, ethanol + propionitrile, and ethanol + butyronitrile, has been studied by monitoring the solvatochromic charge-transfer band of N-alkylpyridinium iodide.It appears that alcohols are preferred over the nitriles.A model for describing the preferential solvation of a dipolar solute in binary solvent mixture has been developed and discussed in relation to other existing approaches.The role of (a) solvent-solvent interaction and (b) difference in size of the component solvent molecules in determining the preferential solvation has also been discussed.
Effect of Added Sodium Iodide on Spectral and Thermodynamic Properties of Methiodides of Some Nitrogen Heteroaromatics in Dipolar Aprotic Solvents
Pal, Mohan,Bagchi, Sanjib
, p. 800 - 807 (2007/10/02)
The longest wavelength band of N-methylpyrazinium iodide and 4-cyano-N-ethylpyridinium iodide, which incidentally is a charge transfer (CT) band, has been studied in various solvents such as acetone, acetonitrile and methyl ethyl ketone at 25 deg C as a function of the concentration of added sodium iodide.The observed blue shift of the CT band with the increase in concentration of the added salt has been explained by considering a suitable model of solvation involving a change of structure of the local environment of the ion pair by the added salt.In addition to the blue shift it has been observed that the intensities of transitions increase with increase in the concentration of the added NaI and finally tend to limiting values, which are significantly higher than the values expected in view of the existence of equilibrium between free ions and ion pairs.These results are, however, consistent with the view that there exists an equilibrium between the two forms of ion pairs, viz. contact form and the solvent separated form, and the addition of NaI does affect the equilibrium between the two forms.Attempts have been made to calculate the associated thermodynamic parameters for different equilibria in solution.
Electronic Effects on the Menschutkin Reaction. A Complete Kinetic and Thermodynamic Dissection of Alkyl Transfer to 3- and 4-Substituted Pyridines
Arnett, Edward M.,Reich, Ronald
, p. 5892 - 5902 (2007/10/02)
The relationship between kinetic and thermodynamic parameters is explored for quaternization of a series of pyridines (mostly 3- and 4-substituted) with several methylating and ethylating reagents in several solvents.The reaction with methyl iodide in acetonitrile is reversible at temperatures in the neighborhood of 100 deg C so that the effect of substituents on free energy, enthalpy, and entropy for activation of the forward and reverse reactions and for the overall quaternization can be determined.A variety of experimental techniques was used to obtain rates over a range of 1013 and to determine enthalpies and entropies of reaction.The results are self-consistent and agree generally with isolated published values for similar systems.The relationship between thermodynamic and activation parameters is examined, and a gross disparity is found between free energy and enthalpy behavior compared with that of the entropies.A consistent picture of the quaternization reaction emerges, based on many studies using a variety of mechanistic probes.The transition state is "early" as far as bond formation to the base in concerned but "late" in terms of bond rupture between the transferring alkyl group and the leaving group with solvent reorganization nearly complete.Quaternization of the 3- and 4-substituted pyridines does not follow the reactivity-selectivity principle, but that of 2-substituted pyridines does.The current practice of assigning detailed bimolecular structures to transition states for substitution, addition, or elimination reactions by application of the Hammond postulate is criticized in view of its inability to handle the dominating role of solvation dynamics and because of the considerable difference in potential energy content (and therefore structure) between the transition states and the reactants or products.
