74 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES
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It should be borne in mind that since the advent of chromatography, it isnow possible to separate and identify the constituents of complex mixtures
which formerly presented some difficulty. It therefore seems desirable that some
of the existing data on the composition of nitration products, particularly those
obtained in earlier studies should be re-examined using up to date techniques.
Finally attention must be drawn to the fact that the orienting effect of the nitro
group in nucleophile and radical reactions usually differs from that in electrophilic
reactions, and instead of meta orientation, ortho or para orientation takes place. The
corresponding observations are referred to in chapters dealing with nucleophile and
radical substitutions of nitro compounds (pp. 204, 207 and 212 respectively).
A monographic description of aromatic nitration and modern approach to
substitution rules was recently given by de la Mare and Ridd [78a].
SIDE REACTIONS IN THE NITRATION PROCESS
A nitration reaction is always accompanied by side reactions which depend
on such different factors as the nature of the substance being nitrated, the com-
position of the nitrating acid and the general nitration conditions.
Thus, oxidation reactions occurring along with a nitration reaction are partic-
ularly strong, whenever the aromatic ring is liable to such a reaction (e.g. oxidation
of phenol to oxalic acid, oxidation of methyl groups in benzene homologues to
hydroxymethyl and carboxyl group, oxidation of naphthalene to phthalic acid etc.).
According to Nightale [79] the action on polyalkylbenzene of concentrated nitric
acid (d = 1.5) leads to oxidation of an alkyl group to yield an alcohol and possibly
a nitrate, e.g.:
An aromatic nucleus not yet substituted with the nitro group is also readily
oxidized to form phenols. That is the reason why certain quantities of nitrophenols
are formed when nitrating benzene to nitrobenzene, and certain nitrocresols when