SIMILARITIES AND DIFFERENCES IN ACTIVATION OF SMALL ALKANES BY LIQUID AND SOLID STRONG ACIDS - AN NMR, MS, AND UV SPECTROSCOPIC STUDY

摘要

The regioselectivity of H/D exchange occurring between isobutane and strong solid acids such as D2O exchanged sulfated zirconia and acidic zeolites has been reinvestigated with increasing contact times on D2O-exchanged USY zeolite and the results compared with those obtained by using 98% D2SO4, As expected, during the initial stage, both on the solid and in the liquid acid only the primary hydrons of isobutane were exchanged for deuterons. However, with aging catalysts, deuterium is slowly introduced also in the tertiary position of isobutane, by a mechanism related to the formation of polyenylic ions which could be monitored by UV spectroscopy. When the catalyst is repeatedly replaced by fresh material, isobutane can be completely selectively deuterated on the primary position with both acids, The MS and NMR spectra show however that the isotopologs distribution in partially deuterated isobutane is very different when D2SO4 is used in comparison with the solid acid. (C) 1997 Academic Press. [References: 29]