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196 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

at 140°C phenazine and its oxide were formed, while at 160°C phenazine only was

obtained. The yield of the reaction was insignificant.

The reaction was improved and its mechanism partly elucidated by several

Russian investigators (Pushkareva and Agibalova [13], Chernetskii, Kipryanov,

Serebrianyi and others [14-17] and Abramova and Postovskii [18]).

It is interesting to note an example of cyclization by the elimination of a

methoxy group by means of a nitro group (Slack and Slack [19]) :

(12)

Among more recent examples of cyclization through a nitro group the

reaction of preparation of phenanthridine might be referred to (Muth, Ellers and

Folmer [20]) :

(13)

The known reduction of two nitro groups to an azoxy group by acting with

strong alkali on nitro compounds (p. 183) can yield cyclic azoxy compounds,

according to Knueppel [153].

A rather unusual example of cyclization by means of a nitro group can also

be referred to in which the nitro group is separated as a molecule of nitrous acid

(Turpin [20a], Angeletti and Brambilla [21]), e.g.:

2-Amine-2’-nitro-4,4’-dimethyldiphenyl

3,7-Dimethyldiphenylene oxide

An interesting instance of elimination of a nitro group was given by Kenner
and co-workers [21a,21b]. It consists in oxidation of 2,6-disubstituted deriva-
tives of p- nitrophenol by lead tetraacetate at room temperature to form deriva-
tives of p- benzoquinone in excellent yields: