Heat capacity changes associated with the solvolysis of tert-butyl chloride in binary alcohol-water systems

Self Cite

The temperature dependence of the rates of hydrolysis of a series of substituted benzyl nitrates in water provided estimates of the heat capacities of activation. These values varied with the substituent over a wide range (−28 → −101 cal mol−1 deg−1).An approximate parallelism has been found to exist between the ΔCp≠ values and kinetic α-deuterium effects obtained for the nitrates and chlorides.While recognizing the existence of specific factors contributing to individual differences, the relative values of these parameters for the individual members of the two series provide a useful measure of the ionic character of the transition state.

“…Rate measurements were made by a conductance method which has been described previously (7). Teniperature control was good to -i 0 .…”

Section: Rate Measuret?7entsmentioning

confidence: 99%

The Nucleophilic Displacement of the Nitrate Group. 1. The Hydrolysis of a Series of Benzyl Nitrates in Water

Koshy¹,

Robertson²

1974

Self Cite

“…Studies have been undertaken by several investigators to test for different theories accounting for the effect of solvent on the rates of chemical reactions in aquo-organic solvent binaries (1)(2)(3)(4)(5)(6)(7)(8)(9)(10). Several factors influence solvent effects on chemical reaction rates; their relative importance seems to be a function of substrate, detailed mechanism of reaction, and experimental conditions.…”

mentioning

confidence: 99%

Solvolysis rates in aqueous – organic mixed solvents. V. Kinetics of the alkaline decarboxylation of trichloroacetate ion in water – ethanol solutions

Diefallah¹,

El-Nadi²

1978

EL-HUSSIENY M. DIEFALLAH and A. M. EL-NADI. Can. J. Chem. 56,2053Chem. 56, (1978. The kinetics of the alkaline decarboxylation of trichloroacetate ion in ethanol-water solutions have been studied over the temperature range 35.0 t o 70.0nC. The rate of reaction is first order with respect to the trichloroacetate ion and is independent of the concentration of t h e hydroxide ion. The reactivity is enhanced by increasing the concentration of ethanol in t h e water-ethanol solutions and the rate of reaction varies with ethanol addition in a nonlinear manner. The rate of reaction increases with the reciprocal of the dielectric constant of t h e medium and the plot of log k vs. 1 / D is approximately linear for solvent mixtures with less t h a n about 0.7 water mole fraction but is strongly curved towards the pure water end. The activation parameters for the reaction show a regular increase in the solvent composition range 0.3 to 1.0 water mole fraction. The results are discussed in terms of the influence of solvent internal pressure and polarity on reactivity and of the increased amount of hydrogen-bonded structure i n the water-rich solutions. [Traduit par le journal]

“…and AS? (2)) when this coefficient was determined for the same compound, t-butyl chloride, solvolyzing in a series of alcohol-water mixtures. The changes AH* and AS* in this study were similar to those reported previously (3).…”

mentioning

confidence: 99%

The Hydrolysis of t-Butyl Chloride in Aquo-Organic Mixtures: Heat Capacity of Activation and Solvent Structure

Robertson¹,

Sugamori²

1972

Self Cite

The temperature dependence of the rate of solvolysis of t-butyl chloride in mixtures of tetrahydrofuran and of acetonitrile in water have been determined. In the high-water range both minor co-solvents lead t o a reduction in the value ofAHf similar to that found previously where alcohol was the co-solvent. However, a remarkable difference in the values of A C~ across the same concentration range reflected a difference in the effect of these two co-solvents on the structural properties of the several solvent media. Where tetrahydrofuran or alcohols are the mirior co-solvent, AC,f becomes much more negative until that concentration is reached where the quasi-aqueous structure collapses. Where acetonitrile is the minor co-solvent A C~ becomes more positive relative to the value found for hydrolysis in water until a value of about -40 cal deg-' mol-' is reached. The implication of these findings concerning the nature of solvation of weakly polar solutes in such mixtures is discussed.On a determine I'influence de la temperature sur la solvolyse du chlorure de r-butyl dans des melanges de tetrahydrofuranne et d'acetonitrile dans l'eau. Dans le domaine de haute concentration en eau, les deux co-solvants mineurs menent a une rtduction de la valeur de AH+ semblable a celle qu'on a trouve precedemment, ou I'alcool Ctait le co-solvant. Toutefois, une difference remarquable dans les valeurs de A C ,~ dans le meme domaine de concentration reflete une difference de I'effet de ces deux co-solvants sur les proprittes structurales des differents milieux de solvants. Lorsque la tttrahydrofuranne ou les alcools sont le co-solvant mineur, A C~ devient beaucoup plus negatifjusqu'a ce qu'on atteigne la concentration ou la structure quasi-aqueuse s'effondre. Lorsque l'acetonitrile est le co-solvant mineur, A C~ devient plus positif comparativement a la valeur qu'on trouve pour I'hydrolyse dans I'eau, jusqu'a ce qu'on atteigne une valeur d'environ -40 cal deg-' mol-I. On discute de I'implication de ces rtsultats relativement a la nature de la solvatation des solutes faiblement polaires dans de tels melanges.