A STUDY OF THE METALATION REACTION USING HYDROGEN ISOTOPES

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1963

OSTI ID:4630956

Barton, K R

The prinrary kinetic hydrogen isotope effects in the metalation of thiophene with n-butyllithium were studied. The protium-deuterium isotope effect (k/sub H//k/sub D/) was established to be 6.6 plus or minus 0.3 at 35 deg . This value is in close agreement with the theoretical value calculated on the basis of the zero-point-energy approximation. A strong protiumtritium isotope effect was also found in this reaction. A definitive value for k/sub H//k/sub T/ was not established, but the data obtained indicate that the rate-constant ratio approaches the theoretical maximum value predicted by the zero-pointenergy approximation, k/sub H//k/sub T/ = 17. Since the isotope effects were found to be relatively strong, the cleavage of the carbon-hydrogen bond at the position to be metalated appeared to be considerably advanced in the transition state leading to proton removal. The agreement between theoretical and experimental values was an indication of the validity of the zero-point-energy approximation for this system. These observations are in accord with the protophilic'' view of the metalation mechanism. The metalation of thiophene in the 2-position was found to be an essentially quantitative process. No evidence of 3-metalation could be detected in a vapor phase chromatographic analysis of the metalation product. Excess quantities of n-butyllithium produced 2,5-dimetalation in the thiophene molecule. The proton transfer in the metalation reaction of thiophene and t- butylbenzene with n-butyllithium and n-butylpotassium, respectively, was followed by deuterium substitution. Deuterium displaced by the metal atom was found to be transferred to the carbon atom of the metalating agent which originally carried the carbon-to-metal bond. There was no evidence to indicate that the beta-carbon atom of the metalating agent becomes involved in the metalation sequence. This is an indication of proton abstraction by a primary carbanion and is in agreement with the 4-member transition state proposal of Bryce-Smith. (Dissertation Abstr.)

• Research Organization: Originating Research Org. not identified
• NSA Number: NSA-17-037250
• OSTI ID: 4630956
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

BENZENE
BINDING ENERGY
BUTYL RADICALS
CHEMICAL REACTIONS
CHEMISTRY
DEUTERIUM
HETEROCYCLICS
HYDROGEN
ISOTOPE EFFECTS
LITHIUM COMPOUNDS
ORGANIC SULFUR COMPOUNDS
ORGANOMETALLICS
POTASSIUM COMPOUNDS
REACTION KINETICS
THIOPHENE
TRITIUM