Kinetic solvation pressure: a measure of environmental effects on reaction rates. 1. Application to hydrophobic systems
A quantity termed kinetic solvation pressure is defined as (/partial derivative//Delta/G/sup /double dagger////partial derivative//anti/V)/sub T/, where /anti/V is the reactant molar volume. It is identified with the difference in the amount of isothermal work, per unit volume expansion necessary to create a solvation cavity in a particular medium, upon transition-state complex formation. The quantity was evaluated for the hydrolysis of carboxylic esters mediated by different hydrophobic catalysts and was found to be equal to +26 J cm/sup /minus/3/ for the acid-catalyzed hydrolysis of n-alkyl acetates in water solvent; but it becomes negative when macro- or supramolecular acids were used as catalysts: /minus/16 J cm/sup /minus/3/ for Dowex 50W-X2, /minus/43J cm/sup /minus/3/ for poly(styrenesulfonic acid), /minus/64 J cm/sup /minus/3/ for dodecylsulfuric acid micelles. These results suggest the action of hydrophobic forces in enhancing the catalytic power of the supermolecules, relative to aqueous hydrogen ion. No such effect is seen in aqueous acetone or when more hydrophilic acetates are used as substrates. Kinetic solvation pressure for enzyme-catalyzed ester hydrolysis is five times more negative than for the resin system, indicating the full action of hydrophobic forces in the catalytic process.
- Research Organization:
- Univ. of Costa Rica, San Pedro
- OSTI ID:
- 5830620
- Journal Information:
- J. Am. Chem. Soc.; (United States), Vol. 110:18
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBOXYLIC ACID ESTERS
HYDROLYSIS
INORGANIC ACIDS
CATALYTIC EFFECTS
CATALYSIS
CATALYSTS
CHEMICAL REACTION KINETICS
EXPERIMENTAL DATA
MICELLAR SYSTEMS
SOLVATION
THERMODYNAMICS
CHEMICAL REACTIONS
DATA
DECOMPOSITION
ESTERS
HYDROGEN COMPOUNDS
INFORMATION
KINETICS
LYSIS
NUMERICAL DATA
ORGANIC COMPOUNDS
REACTION KINETICS
SOLVOLYSIS
400201* - Chemical & Physicochemical Properties