Regioselectivity of the nitration of phenol by acetyl nitrate adsorbed on silica gel

The reaction of phenol with acetyl nitrate in chloroform gives nitrophenol with an ortho/para ratio of 1.8. This ratio increase to 13.3 when the react ion was carried out with acetyl nitrate pre-adsorbed on dry silica gel. Sil ica may be acting as a template to bring phenol close to acetyl nitrate by hydrogen bonds forming a ternary complex, which undergoes a six-center rear rangement to o-nitrophenol. The formation of this ternary complex is evalua ted by ab initio molecular orbital calculation, (C) 1999 Elsevier Science L td. All rights reserved.