Quantitative assessment of solvent-sorting effects. 1. A Menschutkin reaction in mixed solvents

Abstract

The second-order rate constant /capp for the reaction between (C2H5)3N and CH3I has been determined at 30.0 °C in cyclohexane and in mixtures of cyclohexane with variable amounts (up to ca. 0.3 M) of the following cosolvents (S); 7V,/V-dimethylacetamide, cyclohexanecarbonitrile, cyclohexyl methyl ketone, butanone, tetrahydrofuran, ethyl acetate, cyclohexyl chloride, methyl cyclohexanecarboxylate, cyclohexyl methyl ether, dibutyl ether, nitrobenzene, 7V,(V-dimethylbenzamide, benzonitrile, acetophenone, benzophenone, methyl benzoate, diphenylmethane, anisole, chlorobenzene, fluorobenzene, 1,2-diphenylethane, triphenylmethane, benzene, 1,4-dichlorobenzene, toluene, and p-xylene. Within the limits of experimental error, the following have been found: (1) The activity coefficients of the reagents are practically unaffected by the added cosolvent. (2) For low cosolvent concentrations, &app is related to the concentration of S by the equation km = kQ + kc[S], where k0 is the reactioh rate in pure cyclohexane. (3) In all cases, the catalytic effect of S is quite large: it amounts to ca. 50% of the lowering of the activation free energy of the reaction, observed on going from pure cyclohexane to pure S. (4) This major effect is largely underestimated by the Onsager-Kirkwood model. (5) The catalytic efficiency of aromatic cosolvents of low or zero dipolarity is over 1 order of magnitude larger than predicted by this model. This is traced to electrostatic interactions involving higher multipoles and to London forces. (6) Although a fraction of the catalytic effect can be attributed to a "general dielectric" contribution, these and other results strongly suggest that this reaction can proceed through a true termolecular channel.

Dielectric enrichment in binary solvent mixtures. The intramolecular hydrogen bond in N-alkyl-substituted o-nitroanilines. Substituent effects

“…[9]), which coincides with literature data (14) and is interpreted as due to the hydrogen bond donor ability of the H amino group not involved in the intramolecular hydrogen bond.…”

“…The importance of such phenomena has been recognized not only for spectroscopic studies but also for the interpretation of equilibrium and kinetic data (6)(7)(8)(9).…”

Dielectric Relaxation and Solvation Dynamics in a Room-Temperature Ionic Liquid: Temperature Dependence

“…Here we consider an effective solvent polarity measure, determined as the solvatochromic shift of the Franck–Condon (FC) excitation energy of chromophores. − The empirical polarity scale thus defined, such as the Kosower Z factor and E T (30), , gauges the solvating power of solvents, viz., solvent-induced stabilization of dipolar solutes. While this scale correlates well with ε 0 , especially for aprotic dipolar solvents, it yields considerably higher polarity for, e.g., nondipolar but quadrupolar solvents, such as benzene and supercritical carbon dioxide, than their ε 0 values. , This discrepancy arises from electrostatic interactions between the solute dipole and solvent quadrupole moments that are not accounted for in the conventional dielectric constant. − Since these interactions play an important role in solvent reorganization, the empirical polarity scale offers a better measure than ε 0 to describe solvation effects in various charge transfer and shift processes in this solvent class. − Analogously, due to ion monopole–solute dipole interactions, the solvating power and thus effective polarity of RTILs are substantially higher than the predictions made on the basis of their static dielectric constants. This trend was demonstrated by many earlier experiments − and simulations, − ,, where solvation stabilization of polar solutes in various RTILs was found to be comparable to and even exceed that in highly dipolar solvents.…”

Solubility of Water in a Benzene−Cyclohexane Mixture

“…In this article, we apply the CQS description to study solvation in binary mixtures of nonpolar and quadrupolar solvents. It has been found that quadrupolar solvents, when mixed with nonpolar solvents 20 of comparable dielectric constants, enhance the effective polarity of the medium considerably even at small concentrations, analogous to the effect produced by dipolar solvents. , One well studied example is kinetics of Menshutkin reactions . When benzene is added as a cosolvent to cyclohexane, the reaction rate between, e.g., triethylamine and iodomethane in the mixture increases rapidly with the mole fraction of benzene.…”

“…When benzene is added as a cosolvent to cyclohexane, the reaction rate between, e.g., triethylamine and iodomethane in the mixture increases rapidly with the mole fraction of benzene. Its rate constant in pure benzene is larger than that in pure cyclohexane by nearly 4 orders of magnitude . Another example is the solubility of water, which was found to increase with the benzene concentration in the binary mixture of benzene and cyclohexane …”