By refluxing hex-1-ene, hept-1-ene, or oct-1-ene in hexane solution with one of a range of cation-exchanged montmorillonites, the alkenes are converted to the corresponding bis-sec-alkyl ethers. The structures of the ethers may be demonstrated by a combination of gas-liquid chromatography and spectroscopy, but they cannot practicably be prepared by any other method. A number of cations facilitate conversion, the most efficient being Cu2+, Fe2+ and Fe3+, Cr3+, and Al3+: Intercalation is a prerequisite for the reaction which involves transfer of oxygen from hydration shell water held in the interlamellar region to the alkene. Collapsed (strongly dehydrated) montmorillonites do not facilitate the conversion which, for the expanded silicates, is characterized by an optimal water content for a given cation. Thus for Cu2+-exchanged bentonite the optimal metal-water ratio is 1:12 and under these circumstances 100% conversion of usable interlamellar water to ether is achieved. Use of other sheet structures, e.g., Cu(UO2)2(PO4)2 · 6H2O, failed to convert the alkenes, while with Cu2+-exchanged synthetic hectorites and fluorohectorites the reaction was not clean, the ether being only one of a number of products. It has not yet proved possible to make the reaction self-sustaining by constant addition of water. © 1979.