Date of Award
1985
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
This thesis describes the synthesis of three methyl (omega)-(dimethyl- amino)alkanesulfonates and the experiments used to determine the mechanism of their rearrangements to the corresponding (omega)-(trimethylammonio)alkanesulfonates. Since existence of an intra- molecular pathway would represent the first example of an endo- cyclic methyl transfer, kinetic and double-label crossing experiments were used to determine the molecularity of these rearrangements. Methyl 4-(dimethylamino)butane-1-sulfonate, at concentrations ranging from 0.2 M to 2.0 x 10('-4) M in chloroform, was found to form 4-(trimethylammonio)butane-1-sulfonate exclusively via an inter- molecular pathway and the results are consistent with an effective molarity of less than 3 x 10('-5) M for the endocyclic process. Similarly, the formation of 2-(trimethylammoniomethyl)phenylmethanesulfonate from methyl 2-(dimethylaminiomethyl)phenylmethanesulfonate in benzene with initial ester concentrations ranging from 0.2 M to 5 x 10('-4) M was found to occur via intermolecular methyl transfer and these results imply that the effective molarity for the endocyclic process is less than 2 x 10('-5) M. For the rearrangement of methyl 2- 2-(dimethylaminomethyl)phenyl ethanesulfonate to 2- 2-(trimethylammoniomethyl)phenyl ethanesulfonate in benzene, the crossing experiments provided conclusive proof for the existence of both intramolecular and intermolecular pathways. From the dependence of the intra to intermolecular product ratio on the initial ester concentration, an effective molarity of 2 x 10('-3) M was deduced for the intramolecular process. An example of an endocyclic methyl transfer via a nine-membered cyclic transition state has, therefore, been shown. Collectively, the results imply that concerted nucleo- philic methyl transfer transition states show a marked preference for a linear orientation of the nucleophile, the methyl carbon and the nucleofuge.;Model kinetic studies and an ('18)O-labelling experiment which made use of an ('18)O isotope effect on ('13)C NMR chemical shifts showed that the intermolecular pathway for the rearrangements is a two step process. An intermolecular methyl transfer between two molecules of the amino ester gives an ion pair which then annihilates via N-methylation to give two molecules of the betaine.
Recommended Citation
Mcgarrity, Michael Jerome, "Endocyclic Nucleophilic Methyl Transfer" (1985). Digitized Theses. 1418.
https://ir.lib.uwo.ca/digitizedtheses/1418