Date of Defense
THF, DMTHF, solvent qualities, formation
In Dr. John E. Davis' study of the influence of chiral solvents on the stereoselectivity in reactions of Grignard reagents , greater optical activity was expected by the use of more basic derivatives of the solvent tetrahydrofuran (THF). It was thought that the inductive effect of the methyl groups on 2,5-dimethyl-tetrahydrofuran (DMTHF) would enhance its solvent qualities (basicity) by increasing the electron density of the oxygen atom on the THF ring. Thus, tighter association between the oxygen atom of the solvent and the magnesium atom of the Grignard reagent would be achieved.
However, several of Dr. Davis' reactions, such as the simple formation of secondary alcohols, did not proceed in DMTHF. In an attempt to estimate the amount of available benzyl carbanion, benzyl magnesium bromide was prepared in DMTHF and quenched with deuterium oxide. The extent of deuterium in corporation was then determined by analyzing the aliphatic to aromatic proton ratio of toluene on the nuclear magnetic resonance (nmr) spectrum. It was found that no deuterium incorporation had occurred; i.e. there was onehundred percent normal toluene. This meant that the benzyl carbanion had been transformed by proton abstraction, presumably from the very basic solvent, before quenching with deuterium oxide.
Dr. Davis abandoned DMTHF and continued his studies in stereoselectivity using other solvents. The DMTHF anomaly was pursued no further. It has been the objective of this study to reconfirm Dr. Davis' findings, to determine if this is a general reaction or specific reaction, and attempt to locate the site of proton transfer.
Hart, Tadhg, "Reactions of Grignard Reagents in 2,5-Dimethyltetrahydrofuran" (1981). Honors Theses. 714.
Honors Thesis-Campus Only