Lídia M. P. C. Albuquerque

Calorimetric study of the solution process of tetramethylsilane in alcohols

Abstract Calorimetrically measured enthalpies of solution of tetramethylsilane into 16 alcohols, containing from 1 to 6 carbon atoms, are reported at 25°C and infinite dilution. These values are combined with the vaporization enthalpy of the solute to obtain standard enthalpies of gaseous tetramethylsilane and data are analysed in terms of the solvent structures. The solution functions for tetramethylsilane (TMS) are compared with the solution functions for tert-butyl halides (t-BuX) in order to obtain information on ert-butyl halide-alcohol interactions. For this purpose, values of solution enthalpies are also determined for tert-butyl chloride, bromide and iodide in pentan-3-ol, 2-methylbutan-2-ol and hexan-1-ol. The limitations of the use of TMS as “inert” model solute of t-BuX are discussed. However, the application of the Onsager reaction field theory is found to be useful in the analysis of the influence of the eccentricity factor on the interaction enthalpy and leads us to conclusions regarding the relative importance of dipolar solute-solvent interaction and solvent reorganization on the solution process of t-BuX in alcohols.

Linear solvation-energy relationships: solvolytic reactions of t-butyl bromide and t-butyl iodide in hydroxylic solvents

Solvent effects on the solvolytic reactions of ButBr and Butl in water, and 12 monoalcohols and 10 dialcohols, from 1 to 5 carbon atoms, have been analysed in terms of linear solvation energy relationships. The experimentally determined rate constants, at 25 °C, are well correlated through equations of the form log k=a0+a1g(η)+a2ETN+a3C where g(η) is a function of the refractive index, ETN is the normalized Dimroth and Reichardt parameter and C is the solvent cohesive pressure. The correlation analysis revealed significant information on the solvent–solvent–solute interactions. It is also shown that results are in good agreement with previous analysis using different approaches and other sets of solvents.

The enthalpies of solution of 2-chloro-2-methylpropane, 2-chloro-2-methylbutane and 3-chloro-3-methylpentane in mono- and dialcohols at 298.15 K

Abstract The enthalpies of solution at infinite dilution of 2-chloro-2-methylpropane in 9 dialcohols and of 2-chloro-2-methylbutane and 3-chloro-3-methylpentane in 19 mono- and dialcohols, at 298.15 K, were measured using a solution calorimeter. These values are discussed in terms of solute-solvent interactions. Together with previous data, this information provides a thermodynamic picture of the effect of the size of the alkyl chlorides and the structure of the alcohols.

Solution enthalpies of 2-chloro-2-methylpropane in the binary alcoholic mixtures methanol—1,2-ethanediol, ethanol—1,2-ethanediol and 2-methoxyethanol—1,2-ethanediol

Abstract The enthalpies of solution at infinite dilution of 2-chloro-2-methylpropane ( t -BuCl) in methanol—1,2-ethanediol, ethanol—1,2-ethanediol and 2-methoxyethanol—1,2-ethanediol solvent mixtures were measured at 298 K using a calorimetric technique. These values were determined for nine different mole fractions of the alcoholic mixtures. The preferential solvating abilities of the various solvents towards t -BuCl are compared and analysed in terms of the molecular structures of the alcohols.

QUANTITATIVE FORMULATION OF REACTIVITY IN TERMS OF SOLVENT AND SUBSTRATE PROPERTIES. SOLVOLYSIS OF TERT-BUTYL HALIDES IN HYDROXYLIC SOLVENTS

Experimental rate constant values for the solvolysis of tert-butyl chloride in 12 alcohols at 25 °C are presented. These results, together with previous data, are well correlated through the linear solvation energy relationship log k=a0+a1 g(η)+a2ENT+a3C where g(η) is a function of the refractive index, ENT is the normalized Dimroth and Reichardt parameter and C is the solvent cohesive energy density. The same is true for tert-butyl bromide and iodide.A statistical treatment relating the experimental values of the solvolytic rate constants of the three halides in the same set of hydroxylic solvents (water, 8 monoalcohols and 10 dialcohols) to the properties of the solvents [g(η), ENT and C] and of the substrate [molar volume (V) and dipole moment (µ)] simultaneously was performed.

Kinetics and activation thermodynamics of the solvolysis of tert-pentyl and tert-hexyl halides in alcohols

The influences of solvent and substrate were interpreted through the values of rate constants and infinite dilution activity coefficients obtained for the solutes 2-chloro- and 2-bromo-2-methylbutane and 3-chloro-3-methylpentane in several monohydric alcohols at 298.15 K.

Solvent and temperature effects on the rate constants of solvolysis of tert-butyl bromide in mono- and di-alcohols

Rate constants, k, for the solvolytic reactions of 2-bromo-2-methylpropane (ButBr) in the monoalcohols propan-1-ol and butan-1-ol and in the dialcohols ethane-1,2-diol, propane-1,3-diol and butane-1,4-diol are reported, at different temperatures. These values, the Arrhenius activation energies, Ea, and the thermodynamic functions of activation, Gibbs energy (Δ‡G⊖), enthalpy (Δ‡H⊖) and entropy (Δ‡S⊖) are interpreted and compared with previous results in methanol and ethanol. According to the Intersecting-state model, the reaction-energy profile is shaped and the solvent effect on the Gibbs energy of activation, Δ‡G⊖, is analysed.At the molecular level, the dominant solvent–solute interactions are examined. The results show that changes in Ea. (or Δ‡H⊖) most affect the changes in the k values when dialcohols are used in place of monoalcohols; Δ‡S⊖ seems to control the differences in the k values within the set of monoalcohols.