Date of Award
12-2009
Degree Type
Thesis
Degree Name
Master of Science (MS)
Department
Chemistry
First Advisor
Alfons Baumstark - Chair
Second Advisor
Pedro Vasquez
Third Advisor
Markus Germann
Abstract
The epoxidation of a series of α,β-unsaturated esters by dimethyldioxirane was studied. Second order rate constants were determined under pseudo first order conditions. The epoxide of each ester upon full conversion was found to be the only isolable product. Second order rate constants for the cis-like ethyl tiglate showed a 4 fold increase over that of trans-like angelic methyl ester. The ester substituent was found to have little effect on overall rate constants. A comparison of a relatively strained cyclopentene carboxylate to the cyclohexene carboxylate showed a 2 fold increase in selectivity for the former. Ethyl methacrylate displayed unexpected reactivity toward dioxirane; undergoing reaction faster than more substituted electron rich alkenes. Computer modeling studies using the AM-1 and density functional approaches were carried out to gain insights into the mechanistic aspects of the reaction. The esters in general favored the S-cis conformation or were evenly distributed among S-cis and S-trans except for the ethyl methacrylate case. The AM-1 approach did not predict the reactivity of open chain esters. The density functional approach predicted the relative reactivity of seven of the nine esters but could not predict the reactivity when the R1 group was substituted. One possible explanation is that the computer model predicts the methyl groups of the dioxirane to be positioned over the R1 group in the lowest energy of all other esters, but steric clash prevents this for angelic methyl ester and ethyl 3,3 dimethyl acrylate.
DOI
https://doi.org/10.57709/1234339
Recommended Citation
Sansone, John P., "The Kinetics of Epoxidation of A,B-Unsaturated Esters by Dimethyldioxirane: A Mechanistic Study." Thesis, Georgia State University, 2009.
doi: https://doi.org/10.57709/1234339