Presentation Title

Mechanistic Study of 1,8-diazabicyclo[5.4.0]undec-7-ene Catalyzed Esterification of Acylimidazoles

Faculty Mentor

Stephen Heller

Start Date

17-11-2018 12:30 PM

End Date

17-11-2018 2:30 PM

Location

CREVELING 34

Session

POSTER 2

Type of Presentation

Poster

Subject Area

physical_mathematical_sciences

Abstract

The bicyclic amidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), is an extremely effective catalyst for ester and amide formation. It was previously shown that, in the presence of DBU, acylimidazoles, electrophilic carboxylic acid derivatives, react quickly with alcohols to form esters; however, without the catalyst, this reaction proceeds at an extremely slow rate. Despite its intriguing catalytic ability, the exact function and mechanism of DBU is not yet known. A detailed mechanistic understanding of the role of DBU in these acylations can be applied to vastly different reactions and provide an efficient way to create molecules with desired functions. A study of the mechanism of DBU catalysis will be discussed, including a kinetic model for ester formation, catalyst poisoning studies, and investigation of solvent effects on the rate of esterification. The reaction was determined to be first order with respect to the concentration of alcohol, electrophile, and DBU using the isolation method. Evaluation of solvent effects revealed that the rate of esterification increases as solvent polarity increases, but with some notable exceptions. Additionally, it was determined that DBU is easily poisoned by the presence of acid. Contrasting mechanistic hypotheses involving Brønsted or hydrogen-bonding catalysis, as well as future investigations to distinguish between these pathways will also be discussed.

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Nov 17th, 12:30 PM Nov 17th, 2:30 PM

Mechanistic Study of 1,8-diazabicyclo[5.4.0]undec-7-ene Catalyzed Esterification of Acylimidazoles

CREVELING 34

The bicyclic amidine, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), is an extremely effective catalyst for ester and amide formation. It was previously shown that, in the presence of DBU, acylimidazoles, electrophilic carboxylic acid derivatives, react quickly with alcohols to form esters; however, without the catalyst, this reaction proceeds at an extremely slow rate. Despite its intriguing catalytic ability, the exact function and mechanism of DBU is not yet known. A detailed mechanistic understanding of the role of DBU in these acylations can be applied to vastly different reactions and provide an efficient way to create molecules with desired functions. A study of the mechanism of DBU catalysis will be discussed, including a kinetic model for ester formation, catalyst poisoning studies, and investigation of solvent effects on the rate of esterification. The reaction was determined to be first order with respect to the concentration of alcohol, electrophile, and DBU using the isolation method. Evaluation of solvent effects revealed that the rate of esterification increases as solvent polarity increases, but with some notable exceptions. Additionally, it was determined that DBU is easily poisoned by the presence of acid. Contrasting mechanistic hypotheses involving Brønsted or hydrogen-bonding catalysis, as well as future investigations to distinguish between these pathways will also be discussed.