ADDITION OF ALCOHOLS TO ISOBUTYLENE (Methyl- and Ethyl-Ter-Butyl Ether)

The reaction between isobutylene and methyl and ethyl alcohols is an addition reaction catalyzed by a heterogeneous sulfonated polystyrene resin. When methanol is used a 98% yield of methyl-ter-butyl ether MTBE is obtained:

Ethyl-ter-butyl ether (ETBE) is also produced by the reaction of ethanol and isobutylene under similar conditions with a heterogeneous acidic ion-exchange resin catalyst (similar to that with MTBE):

MTBE and ETBE constitute a group of oxygenates that are currently in high demand for gasoline octane-number boosters. Both MTBE and ETBE have a similar research octane number of 118, but the latter ether has a motor octane number of 102 versus 100 for MTBE.  However, the oxygen content of MTBE is 18.2% compared to 15.7% for ETBE. The lower oxygen content of ETBE is related to the air/fuel ratio, which may not require a change in the automobile carburetors. A comparison between the two ethers regarding phase separation, antiknock behavior, and fuel economy has been reviewed by Iborra et al.