EFFECT OF PRESSURE ON THE ACID-CATALYZED ENOLIZATION OF ACETONE AND ACETOPHENONE IN VARIOUS ETHANOL-WATER SOLVENTS. ORIGIN OF THE ENTHALPYENTROPY COMPENSATION EFFECT
NATIONAL RESEARCH COUNCIL OF CANADA OTTAWA (ONTARIO) DIV OF APPLIED CHEMISTRY
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The effect of pressure, temperature, and solvent composition on the rate of the acidcatalyzed enolization of acetone and acetophenone, and the solvent deuterium isotope effect for the enolization of acetophenone, were measured by following the iodination. The solvent deuterium isotope effect for the enolization of acetophenone in 16.2 ww ethanol-water is 2.50 0.05, which undoubtedly proves that there is a preequilibruium proton transfer. The effect of solvent in the range water to 33.4 ww ethanol in water on the rate of enolization of both acetone and acetophenone is small at atm pressure, but is about four times larger at 3 kbar. This cannot be explained on simple electrostatic grounds, and indicates that any simple electrostatic explanation of the solvent effect at atmospheric pressure is invalid. The volumes of activation for the enolizations are strongly dependent on the solvent. An examination was made of the enthalpy-entropy compensation effect. In general, if the rate of equilibrium constant of a reaction does not change with changing conditions then either the quantities of activation at constatn pressure.
- Organic Chemistry