Rapid fixation of methylene chloride by a macrocyclic amine.
A simple macrocyclic amine is alkylated by methylene chloride to give a quaternary ammonium chloride salt. When methylene chloride is the solvent, the reaction exhibits pseudo-first-order kinetics, and the reaction half-life at 25.0 degrees C is 2.0 min. The reaction half-life for a structurally related, acyclic amine is approximately 50 000 times longer. Detailed calculations favor a mechanism where the methylene chloride associates with the macrocycle to form an activated prereaction complex. The macrocyclic nitrogen subsequently attacks the methylene chloride with a classic SN2 trajectory, and although the carbon-chlorine bond breaks, the chloride leaving group does not separate from the newly formed cationic macrocycle, such that the product is a tightly associated ion-pair. X-ray crystal structures of the starting amine and the product salt, as well as kinetic data, support this mechanism.
Lee
Jung-Jae
JJ
Department of Chemistry and Biochemistry and Walther Cancer Research Center, University of Notre Dame, Notre Dame, Indiana 46556, USA.
Stanger
Keith J
KJ
Noll
Bruce C
BC
Gonzalez
Carlos
C
Marquez
Manuel
M
Smith
Bradley D
BD