Secondary Deuterium Isotope Effects in the Reactions of Carboxylic Acid Derivatives

Journal Article · Tue Dec 20 04:00:00 EST 1960 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja01509a032· OSTI ID:4118460

Bender, Myron L.; Feng, Mary S.

Ethyl acetate-d/sub 3/, acetyl chloride-d/sub 3/, and acetic anhydride-d/ sub 6/ were synthesized. The effect of beta -deuterium substitution on the rates of hydrolysis of these carboxylic acid derivatives was determined. In the basic hydrolysis of ethyl acetate in aqueous solution at 25.0 deg C, k/sub H//k/ sub D/ = 0.90, a reverse isotope effect. In the hydrolysis of acetyl chloride in lO% and 20% water-acetone (v./v.) at -22 deg C, k/sub H//k/sub D/ = 1.51 and 1.62, respectively. The solvolyses of acetyl chloride in cyclohexre containing 0.2665 M ethanol and in 5% wateracetone at 25.0 deg C and the solvolysis of acetic anhydride in water at 2O.O deg C showed essentially no secondary deuterium isotope effect. The secondary deuterium isotope effects that occur in the saponification of ethyl acetate and in the hydrolysis of acetyl chloride in 10% and 20% water-acetone can be explained in terms of differences in hyperconjugation in the ground and transition states of these hydrolysis reactions. It is postulated that the transition state of the hydrolysis of acetyl chloride is similar to an acylium ion and that this increase in positive charge leads to an isotope effect in the same direction as that found in Sn1 solvolyses. Its magnitude depends on the amount of positive charge developed in the transition state, which in turn is a function of the solvating power and dielectric constant of the medium. It is predicted that the secondary deuterium isotope effect in the hydrolysis of ethyl acetate should be the reverse of that found in Sn1 solvolyses, on the basis of the hyperconjugation hypothesis and the known mechanism of the reaction in which the positive charge on the carbonyl carbon atom of the ester in the ground state decreases in the transition state. (auth)

• Research Organization: Illinois Inst. of Tech., Chicago
• Sponsoring Organization: USDOE
• NSA Number: NSA-15-007261
• OSTI ID: 4118460
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 24 Vol. 82; ISSN 0002-7863
• Publisher: American Chemical Society (ACS)
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ACETATES
ACETIC ACID
ACETONE
ACETYL RADICALS
ATOMS
CARBON
CARBONYLS
CHEMICAL REACTIONS
CHEMISTRY
CHLORIDES
CYCLOALKANES
DEUTERIUM
DIELECTRICS
ESTERS
ETHANOL
ETHYL RADICALS
HEXANE
HYDROLYSIS
ISOTOPE EFFECTS
MACHINE PARTS
MECHANICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
PREPARATION
REACTION KINETICS
SAPONIFICATION
SERVOMECHANISMS
SOLUTIONS
SOLVOLYSIS
TRANSIENTS
TRANSITION STATES
WATER