Nitration nitric acid-hydrogen fluoride-boron

Numerous Lewis acids promote the formation of nitronium ions when in the presence of nitric acid. Nitric acid-boron trifluoride, and the nitric acid-hydrogen fluoride-boron trifluoride reagents described by Olah are practical nitrating agents the latter provides a convenient preparation of nitronium tetrafluoroborate. Olah reports that nitric acid-magic acid (FSOsH-SbFs) is extremely effective for the polynitration of aromatic substrates. 

Another aspect of my early research in Budapest was in nitration chemistry, specifically the preparation of nitronium tetrafluoroborate, a stable nitronium salt. 1 was able to prepare the salt in a simple and efficient way from nitric acid, hydrogen fluoride, and boron trifluoride. 

A convenient method for the preparation of nitronium tetrafluoroborate involves treating a mixture of absolute nitric acid or an alkyl nitrate " with anhydrous hydrogen fluoride and an excess of boron trifluoride. Pure nitronium triflate can be synthesized by treating triflic anhydride or triflic acid with dinitrogen pentoxide in an inert solvent. Other methods for nitronium salt synthesis are discussed by Olah. ... 

The formation of the nitronium ion is critical to the success of nitration. The purpose of the sulfuric acid is to generate the nitronium ion other acids such as perchloric acid, hydrogen fluoride and boron trifluoride are also effective. Nitric acid alone contains only relatively small concentrations of nitronium ion and hence is not an effective nitrating agent, except with very reactive substrates. 

Nitronium tetrafluoroborate, from nitric acid, boron trifluoride, and hydrogen fluoride, 47, 56 in nitration of aromatic rings, 47,... 

However, it is not only sulphuric acid added to nitric acid that increases the latter s nitrating properties, Such substMices as boron fluoride (R. J. Thomas et al. [46]) or hydrogen fluoride (Simons et al. [47]) when added to nitric acid have a similar effect. 

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