Amide/Iminium Zwitterionic Catalysts for (Trans)esterification: Application in Biodiesel Synthesis

A class
of zwitterionic organocatalysts based on an amide anion/iminium
cation charge pair has been developed. The zwitterions are easily
prepared by reacting aziridines with aminopyridines. They are catalytically
applicable to transesterifications and dehydrative esterifications.
Mechanistic studies reveal that the amide anion and iminium cation
work synergistically in activating the reaction partners, with the
iminium cationic moiety interacting with the carbonyl substrates through
nonclassical hydrogen bonding. The reaction can be applied to large-scale
synthesis of biodiesel under mild conditions.