Exchange reactions of alkanes containing quaternary carbon atoms over supported metal catalysts

Abstract

A comparison has been made of the exchange reactions with deuterium of 2,2-dimethylpropane (DMP), 2,2,3,3-tetramethylbutane (TMB) and 2,2,4,4-tetramethylpentane (TMP) over supported catalysts containing iridium, palladium, platinum or rhodium at temperatures in the neighbourhood of 400 K. Reactions were followed mass-spectrometrically and products were also examined by deuterium n.m.r. spectroscopy. Four processes or mechanisms were found to contribute to different extents with the various hydrocarbon–metal systems. These were (I) stepwise exchange, (II) methyl–group exchange, and more general multiple exchange involving(III)αγ-diadsorbed or (IV)αδ-diadsorbed intermediates. Some isomerisation of TMP was observed to occur simultaneously with exchange with the TMP–rhodium system.