Catalysis of transimination by rate-limiting proton transfer to buffer bases

Journal Article · Wed Feb 13 04:00:00 EST 1980 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00524a018· OSTI ID:5279668

Fischer, H; DeCandis, F X; Ogden, S D; Jencks, W P

General base catalysis of the hydroxylaminolysis of benzhydrylidenedimethylammonium ion gives a Bronsted plot that follows the Eigen curve expected for rate-determining trapping of the initially formed addition intermediate by proton transfer to a buffer base or water. The solvent deuterium isotope effects for catalysis by oxy anions exhibit a maximum at the break point of the Eigen curve, close to the estimated pK/sub a/ for the addition intermediate. This maximum can be accounted for by a partial change in rate-limiting step of the proton-transfer process near ..delta..pK = 0. Water shows a positive deviation from the Bronsted plot and a solvent isotope effect of k/sub H/sub 2/O//k/sub D/sub 2/O/ = 4.7 that provide additional evidene for the trapping mechanism. The addition of glycerol increases the rate of the base-catalyzed reaction; much larger increases are observed with ethylene glycol and methanol. In contrast, the base-catalyzed hydrolysis of the cationic imine follows a linear Bronsted plot (..beta.. = 0.24), with a negative deviation for catalysis by water, and gives a constant value of k/sub H/sub 2/O//k/sub D/sub 2/O/ = 1.9 +- 0.2. A concerted mechanism of base-catalyzed attack by water is suggested for this reaction.

• Research Organization: Brandeis Univ., Waltham, MA
• OSTI ID: 5279668
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 102:4; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400302* -- Organic Chemistry-- Isotope Effects-- (-1987)
AMINES
BUFFERS
CHEMICAL REACTIONS
DATA
DATA FORMS
DEUTERIUM
EXPERIMENTAL DATA
HEAVY WATER
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROXIDES
HYDROXYL RADICALS
INFORMATION
ISOLATED VALUES
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
NUCLEI
NUMERICAL DATA
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
OXYGEN COMPOUNDS
RADICALS
STABLE ISOTOPES
WATER