Isomerization of endo-tetrahydrodicyclopentadiene over clay-supported chloroaluminate ionic liquid catalysts

Various halide salts with different alkyl lengths were allowed to intercalate into the layer structure of sodium montmorillonite clay through an ion exchange reaction. Intercalation of 1-hexadecyl-3-methylimidazolium chloride, hexadecyltrimethylammonium bromide, dihexadecyldimethylammonium bromide, and tributylhexadecylphosphonium bromide could expand the spacing of the silicate layers from 12 to 37-41 angstrom (measured by X-ray diffraction). The modified clays were pretreated with the pyridine hydrochloride/AlCl3 mixture and used for suitably supporting a chloroaluminate ionic liquid catalyst for the isomerization of endo-tetrahydrodicyclopentadiene into the corresponding exo-isomer. Nearly quantitative conversion to the desired product and nearly quantitative selectivity were observed for the newly developed clay-supported ionic liquid catalysts, which were proven to be recyclable. (C) 2009 Elsevier B.V. All rights reserved.