Samuel H. Graham

Selective chemical conversions using sheet silicate intercalates: Low-temperature addition of water to 1-alkenes

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.

Catalyzed reactions of organic molecules at clay surfaces: Ester breakdown, dimerizations, and lactonizations

The use of montmorillonites as Bronsted acid catalysts has been investigated for a range of reactions: (i) decomposition of cyclohexyl esters, (ii) dimerization of propenylbenzenes, and (iii) the lactonization of cyclooctene-5-carboxylic acid. The ester cracking can be accomplished with a wide range of ion-exchanged clays, with conversions of up to 98% after 7 hr at 140 °C (Al3+-montmorillonite). Although the cracking rate is dependent upon the interlayer cations in the clay, at least some of the activity is due to sites on the external surfaces of the clay particles. The dimerization of anethole (1-(4-methoxybenzene)-prop-1-ene) is efficient when using either di- or trivalent cation-exchanged montmorillonites, e.g., 44% recoverable yield of metanethole is attainable in 1 hr at 126 °C compared with literature procedures giving 24% yields in 7 hr. For a second propenylbenzene, isohomogenol (1-(3,4-dimethoxybenzene)-prop-1-ene), dimerization could only be effected using the very acidic trivalent ion-exchanged montmorillonites. Yields were typically 60% after 5 hr at 69 °C. It is not apparent why there are large differences in reactivity between anethole and isohomogenol, which are closely related structurally. Cation-exchanged montmorillonites can also catalyze the conversion of cyclooctene-5-carboxylic acid initially to 4-cyclooctane carbolactone and then to a variety of other lactone products. The rate of consumption of the acid is similar with a variety of ion-exchanged clays, but the subsequent rate of isomerization is cation dependent. For the lactonizations the clay acid catalysts proved no better than liquid phase catalysts in producing a high percentage of one particular lactone.

Selective organic reactions in sheet-silicate intercalates: conversion of 4,4′-diamino-trans-stilbene into aniline

Aniline is produced in good (ca. 45%) yield when the intercalate of montmorillonite and 4,4′-diamino-trans-stilbene is heated, in vacuo, to ca. 300 °C.

Chemical conversions using sheet silicates: simple method for producing methyl t-butyl ether

Copper-exchanged montmorillonite, in which the water of hydration of the interlamellar Cu2+ ions has been exchanged by methanol, readily converts 2-methylpropene into methyl t-butyl ether.

Chemical conversions using sheet silicates: ready dimerization of diphenylethylene

Cation-exchanged montmorillonites function as efficient catalysts for the production of 1-methyl-1,3,3-triphenylindan from 1,1-diphenylethylene at low temperature.

Catalytic conversion using a sheet silicate: hydrogen exchange between hydrocarbons on a synthetic hectorite

1,1-Diphenylethylene and 9,10-dihydroanthracene react smoothly over a synthetic hectorite catalyst to give anthracene and diphenylethane.

Ready conversion of 1,1-diphenylethylene into benzophenone and 1,1-diphenylethane over a synthetic hectorite

Synthetic fluorohectorite serves as an efficient agent for the conversion of 1,1-diphenylethylene into benzophenone and 1,1-diphenylethane.