SELECTIVE ISOTOPIC OXYGEN INCORPORATION INTO C-5 AND C-6 ETHERS VIA SOLID ACID-CATALYZED REACTION OF METHANOL AND ETHANOL WITH ISOBUTANOL

Reaction of (CH3OH)-O-18 with O-16-containing isobutanol (2-methylprop an-1-ol) over strong acid Nafion-H and Amberlyst-H 35 resin catalysts gave the two distinctly labelled C-5 ethers 1-methoxy(O-16)-2-methylpr opane (also designated as methyl isobutyl ether, O-16-MIBE) and 2-meth oxy(O-18)-2-methylpropane (also designated as methyl tertiary-butyl et her, O-18-MTBE). Reaction of (CH3CH2OH)-O-18 with isobutanol gave the analogously labelled C-6 ethers, O-16-EIBE and O-18-ETBE. These result s show that the isobutyl and tertiary-butyl ethers are formed from the alcohols by distinctly different mechanistic pathways, i.e, the forme r are produced by surface-catalyzed S(N)2 reactions that follow Langmu ir-Hinshelwood kinetics involving competitive adsorption while the lat ter arise via carbenium or olefinic intermediates. There is no pathway for isomerization of the two ethers, MIBE and MTBE, under the reactio n conditions employed.