Acid zeolites as catalysts in organic reactions. tert-Butylation of anthracene, naphthalene and thianthrene

Liquid phase tert-butylation of anthracene, naphthalene and thianthrene to afford 2-tert-butyl plus 2,6- and 2,7-di tert-butyl derivatives were carried out at atmospheric pressure and moderate temperatures (below 100°C) in the presence of a series of large pore zeolites and mesoporous aluminosilicates including HY-100 (Si/Al 2.6), HY-D1 (Si/Al 2.75), HY-D2 (Si/Al 15), Hβ, HMor and MCM-41. The activity increases from MCM-41 and Mor to β and Y zeolites, the latter being the most active catalysts. In addition, HY zeolites are much more efficient as catalysts than p-toluenesulfonic acid under the same reaction conditions. As alkylating reagent tert-butyl alcohol was employed in isooctane or carbon tetrachloride. It was found that isooctane itself is a powerful and convenient reagent for the tert-butylation. Mechanistic studies using radical scavengers indicates that in the isooctane alkylation tert-butyl cation is the sole intermediate involved. In the case of thianthrene, the concomitant formation of the thianthrenium radical cation during the alkylation reaction has been observed.