Nitration of bibenzyl by nitronium tetrafluoroborate. Comments on the mechanism of nitration by nitronium salts

Abstract

The addition of a solution of nitronium tetrafluoroborate (ca. 0·2M) in sulpholan to a well-stirred solution of bibenzyl in sulpholan gives a high percentage of dinitrobibenzyls even when the bibenzyl is in five-fold excess. This product composition is shown to be a consequence of nitration during mixing. On the basis of a simple model, it is calculated that the nitronium ions are effectively mixed with ca. 1·2 times the equivalent number of aromatic rings before reaction is complete. This calculation is used to show that the competitive nitration of similar aromatic compounds under these conditions should give apparent relative reactivities of near unity, irrespective of the true relative reactivity of the substrates towards the nitronium ion.