NITRO DERIVATIVES OF PHENOL^481(2)The direct formation of styphnic acid from resorcinol and nitric acid may
also be explained by this series of reactions.
Earlier, Auwers [37] expressed the opinion that phenols when reacted with nitric
acid, could yield dark coloured quinols, e.g.:“Nitroketone”(3)Hydrolysis of chloronitro compounds. The chlorine atom in chlorobenzene
and in its homologues becomes reactive after one or more nitro groups have been
introduced into the ring. This is used widely in the preparation of nitrophenols
and their ethers. The preparation of dinitrophenol, dinitroanisole and dinitro-
phenetole may serve as a classical example (see Chapter XVI).
Oxidation of nitrosophenols. This method is applied when fewer nitro groups
are to be introduced on the ring than those obtained by way of nitration. It is also
applied when a pure product, free from its isomers, is to be prepared, e.g. p- nitro-
phenol from phenol. Direct nitration of phenol yields a mixture of the o- and p- iso-
mers, dinitrophenol being readily formed as a by-product. Similarly dinitroresorcinol
may be obtained by oxidation of dinitrosoresorcinol (p. 537).MANUFACTURE OF DINITROPHENOL BY DIRECT NITRATIONReverdin and de la Harpe’s method [22]This method consists in the sulphonation of phenol to phenolsulphonic acid
which, on heating with nitric acid, is converted into dinitrophenol. In addition
some 2,6-dinitrophenolsulphonic acid is also formed. As the latter remains in
solution the yield of dinitrophenol is lower than the calculated one.
According to Marqueyrol and Lorriette [38], the reaction proceeds as follows: