Abstract: The acid-catalyzed reaction between methanol and isobutene to give methyl-t-butyl ether may be carried out using a cation-exchanged smectite as the catalyst. In 1,4-dioxan solvent at 60°C smectites exchanged with Al3+, Fe3+, or Cr3+ give yields of ∼60% after 4 hr, whereas smectites exchanged with Cu2+, Pb2+, Ni2+, Co2+, Ca2+, and Na+ give less than ∼8% yield. The reaction is efficient only when certain solvents are used, e.g., with Al3+-smectite the yield is ∼5% when using 1,2-dimethoxyethane, diethyleneglycol diethylether, n-pentane, tetrahydropyran, N-methylmorpholine, or tetrahydrofuran solvents compared with ∼60% using 1,4-dioxan solvent (4 hr). Moreover, the effective solvents depend somewhat on the clay interlayer cation. The use of tetrahydrofuran and tetrahydropyran gives ∼35% yields at 60°C (4 hr) with Fe3+- or Cr3+-smectites but ∼4% yield with Al3+-smectite.