Catalytic properties of metal-containing polymethylsiloxanes

Aluminium-, iron-, titanium- and zirconium-containing polymethylsiloxanes were studied as catalysts for acid-catalysed reactions; their surface acidity and the strengths of their acid centres were determined. They appeared to be active for 2-propanol dehydration; the best sample was almost as active as alumina, which is known for its high activity for alcohol dehydration. All metal-containing polymethylsiloxanes (MPS) catalysed double-bond migration and cis-trans isomerization of 2-butene. Some of them also catalysed the synthesis of methyl t-butyl ether, but their activity for this reaction was inferior to that of the resin Amberlyst-15 and some of sulphate-ion modified metal oxides. No cumene conversion occurred on the catalysts studied and no pyridinium ion formation was observed by IR spectroscopy, which points to the absence of strong Bronsted acid sites. The MPS are distinguished by quite large surface areas (86-299 m(2) g(-1)) and are capable of chemisorbing pyridine (0.014-0.047 mmol g(-1)) on their Lewis acid centres.