A new method of nitration of aromatic compounds has been developed by use of stable nitronium salts, first, with nitronium tetrafluoroborate.MOISSAN and LEBEAU,~ using material which probably contained some nitryl fluoride,, obtained evidence of formation of nitrobenzene from benzene. Using pure nitryl fluoride, now readily prepared, Hetherington and Robinson 3 have surveyed its nitrating properties towards organic compounds, alone or dissolved in an inert liquid. Of the organic compounds used some were inert (aliphatic hydrocarbons and deactivated aromatic compounds such as nitrobenzene), some were nitrated normally, and some were destroyed (e.g., aniline, which rapidly gave tars). As expected, those undergoing nitration gave the same nitro-compounds as result from the use of mixed acids. Hetherington and Robinson postulated that the nitration is due to the nitronium ion NO,+, formed by dissociation of the nitryl fluoride in the liquid undergoing treatment. During investigation of the mechanism of nitration Goddard, Hughes, and Ingold * isolated some nitronium salts, [NO,+]X-, e.g., the perchlorate, hydrogen disulphate, neutral disulphate, neutral nitronium trisulphate, and fluorosulphonate. The ionic constitutions assigned were spectroscopically established. The compounds isolated were not sufficiently stable for use as nitrating agents and as yet nothing has been published about the kinetics of reaction of these compounds. Woolf and Emeldus treated oxy-salts with bromine trifluoride and nitrogen oxide, and so obtained a number of nitronium salts, such as the tetrafluoroborate, hexafluorostannate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, and tetrafluoroaurate, but did not refer to their use as nitrating agents. So nothing has beeq known hitherto about the use of stable nitronium salts as nitrating agents.We have found that some nitronium salts, first, nitronium tetrafluoroborate,6 and then the hexafluorosilicate, hexafluoroantimonate, and hexafluorophosphate, are useful nit rating agents.Of the stable nitronium salts it seems that the tetrafluoroborate is the most convenient. It can be prepared by Aynsley, Hetherington, and Robinson's method2 from nitryl fluoride and boron trifluoride, or without the use of elementary fluorine by Schmeisser and Elischer's method, by the reaction of dinitrogen pentoxide with hydrogen fluoride and boron trifluoride in nitromethane. Nitronium tetrafluoroborate, which is a white crystalline compound, is stable in the absence of moisture and is adaptable as a nitrating agent for common use. For instance, with it we have nitrated the compounds listed in the Table, with the yields stated. For the experimental methods see the Experimental section. In the case of nitrogen-containing compounds such as diethyl-and dimethyl-aniline or pyridine the basic nitrogen atom reacts first with the nitronium salt., and isolation of nitrated compounds is complicated.Nitronium hexafluorosilicate, hexafluoroantimonate, and hexafluorophosphate behave similarly as nitrating agents (...
