Weygand/Hilgetag Preparative Organic Chemistry

Replacement of nitrogen by oxygen 343
less preparative importance than that of primary aromatic amines into aromatic
hydroxy compounds.
Primary aromatic amines can be converted into the corresponding hydroxy
compounds in various ways. In some cases this can be done by use of dilute
acid or alkali under specific conditions, but that method is used mainly in
industry and is rarely suitable for laboratory practice. 4-Amino-2,7- and -2,6naphthalenedisulfonic
acid and 8-amino-l,6-naphthalenedisulfonic acid are
converted quantitatively into the corresponding hydroxynaphthalenedisulfonic
acids when their acid salts are heated in water at 180° ; 555 and 2-methoxy-
4-nitroaniline affords 4-nitroguaiacol in 86% yield when boiled for 30 hours with
aqueous sodium hydroxide. 556
A generally applicable procedure for conversion of aromatic amines into
phenols or naphthols consists of "boiling" aromatic diazonium compounds
(for their preparation see page 581). This method will be illustrated here by
some examples.
ArN2 + HSO4- + H2O > ArOH + H2SO4 + N2
Side reactions that occur in this process with diazonium halides and nitrates
prevent the diazotization being effected in nitric or hydrochloric acid solution;
it is necessary to do this in sulfuric acid solution, and the sparing solubility
of the sulfates of aromatic amines necessitates certain departures from the
usual diazotization procedures.
Preparation of m-nitrophenol from m-nitroaniline: 557 A cold mixture of water (450 ml
and concentrated sulfuric acid (330 ml) is poured, with stirring, over finely powdered m-nitroaniline
(210 g), and ice (800 g) is added. When the mixture has become homogeneous, a
solution of sodium nitrite (105 g) in water (250 ml) is run in during 8-10 min from a dropping
funnel until the starch-iodine reaction remains positive. The temperature is kept between 0°
and 5° and the mixture is stirred for a further 5-10 min. Then the m-nitrobenzenediazonium
sulfate is allowed to settle, the supernatant liquid is poured off and the solid washed, if
necessary, with water by decantation in order to purify the salt; filtration is necessary only
when gross impurity is present.
Meanwhile a mixture of water (750 ml) and concentrated sulfuric acid (11) has been
brought to boil in a large (5-1) flask, and to this the liquid decanted from the diazonium salt is run
in from a dropping funnel at such a rate that the mixture remains in lively ebullition for 50 min.
Then the solid diazonium salt is added in small portions, care being taken to avoid losses due
to foaming. After these additions the mixture is boiled for a few minutes and then poured
into a large beaker that is cooled in running water; there it is vigorously stirred while cooling,
so that the dark oily /w-nitrophenol that separates solidifies in as finely divided a state as
possible, rather than in large lumps. When cold, the solid is filtered off, sucked as dry as
possible, and washed with ice-water (450 ml in all). The crude product (170-180 g, 81-86%)
is dried in the air, and is purified by distillation in a vacuum (b.p. 160-165°/12 mm) or by
recrystallization from benzene.
This procedure can be used also for other, relatively stable nitro diazonium
compounds. However, when the diazonium compounds are unstable, their
separation in the solid state is to be avoided. The following directions for
preparation of m-chlorophenol are given by Holleman and Rinkes: 558
555 A. Rieche and H. Seeboth, Ann. Chem., 638,102 (1960).
556 N. L. Drake, H. C. Harris, and C. B. Jager, /. Amer. Chem. Soc, 70, 170 (1948).
557 R. H. F. Manske, Org. Syn., 8, 80 (1928).
558 A. F. Holleman and I. J. Rinkes, Rec. Trav. Chim., 30, 81 (1911).