Selective isotopic oxygen incorporation into C5 and C6 ethers via solid acid-catalyzed reaction of methanol and ethanol with isobutanol

Abstract

Reaction of CH318OH with16O-containing isobutanol (2-methylpropan-1-ol) over strong acid Nafion-H and Amberlyst-H 35 resin catalysts gave the two distinctly labelled C5 ethers 1-methoxy(16O)-2-methylpropane (also designated as methyl isobutyl ether,16O-MIBE) and 2-methoxy(18O)-2-methylpropane (also designated as methyl tertiary-butyl ether,18O-MTBE). Reaction of CH3CH218OH with isobutanol gave the analogously labelled C6 ethers,16O-EIBE and18O-ETBE. These results show that the isobutyl and tertiary-butyl ethers are formed from the alcohols by distinctly different mechanistic pathways, i.e. the former are produced bysurface-catalyzed SN2 reactions that follow Langmuir-Hinshelwood kinetics involving competitive adsorption while the latter arise via carbenium or olefinic intermediates. There is no pathway for isomerization of the two ethers, MIBE and MTBE, under the reaction conditions employed.