Lanthanide(III) complexes of aromatic sulfonic acids as catalysts for the nitration of toluene

Ytterbium(III) complexes of benzenesulfonic acid, Yb(BSA)3, p-toluenesulfonic acid, Yb(Tos)3, and 2-naphthalenesulfonic acid, Yb(NSA)3, were prepared and tested as possible catalyst for the nitration of toluene. With a loading of 5-10 mol% of Yb(BSA)3 and Yb(NSA)3, a quantitative conversion of toluene to nitrotoluene was achieved within 5 h, while Yb(Tos)3 was slightly less active and 77% of nitrated products were obtained. The catalysts can be easily recovered after the reaction, and 1H NMR spectroscopy of analogous diamagnetic lanthanide(III) catalysts showed that the recovered catalysts were identical to the freshly prepared ones. The ratio of ortho:meta:para products was in all reactions 52:6:42, which is consistent with a direct electrophilic attack by the nitronium ion, NO2+. © 2003 Elsevier B.V. All rights reserved.