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NITRATION AGENTS AND METHODS MORE RARELY USED^109

NITRYL FLUORIDE (NITRONIUM FLOURIDE, NO 2 F)

Nitryl fluoride is a gas which liquifies at -73°C and solidifies at ca. -160°C.

Nitryl fluoride was prepared for the first time, by Ruff, Manzel and Neumann

[115] in 1932, by acting with fluorine on nitrogen dioxide. (The earlier report of

Moissan and Lebeau [116] in 1905 is uncertain.) Aynsley, C. Hetherington and

Robinson [117] improved the method in 1954 by acting on dry sodium nitrite

with fluorine.

Nitryl fluoride reacts with sulphuric acid according to the following equation

(Hetherington, Hub and Robinson [118]) :

NO 2 F + H 2 SO 4 -> NO 2 + + HF + HSO 4 - (44)

After that the reaction becomes reversible:

HF + 2H 2 SO 4 <-> HSO 3 F + HSO 4 - + H 3 O+ (45)

On the basis of eqn. (45) it would be expected that nitryl fluoride in sul-

phuric acid is a nitrating agent (besides also possessing fluorinating and sulpho-

fluorinating effects).

NITROGEN TRIOXIDE (NITROUS ANHYDRIDE)

Although solid N 2 O 3 can exist as a pure compound (m.p. ca. -102°), never-

theless in the liquid phase it very soon begins to dissociate, and exists only at low

temperature under an atmosphere containing free nitrogen oxide. At temperatures

above -100°C dissociation begins and the gaseous phase is enriched with nitrogen

oxide, and the liquid phase with the dioxide. Thus, the “blue-green” liquid commonly

described as N 2 O 3 is a solution of greater or smaller quantities of NO 2 in N 2 O 3.

d’Or and Tarte [119], on the basis of the infra-red spectrum of the compound,

have given its constitutional formula as:

(the N-N bond produces an absorption band similar to that given by N 2 O 4 ).
It is assumed that the mechanism of dissociation of nitrogen trioxide involves
its separation into disproportionate amounts of the nitrosonium and nitrite ions:
N 2 O 3 -> NO+ + NO 2 - (46)
Hence the formation of nitroso compounds (C-nitroso- and O-nitroso, i.e. nitrous
acid esters) is possible.

Nitrogen trioxide combines with boron trifluoride to form a complex salt,

the structure of which, as assumed by G. B. Bachman and Hokama [104], should
be either:
(F 3 B<-NO 2 )-NO+ or (F 3 B+NO)-NO 2 +

In consequence of its dual form the compound can act both as a nitrosating (diazo-
tizing) and as a nitrating agent.