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NITRO DERIVATIVES OF PHENOL 483

From 100 kg of phenol 140 kg of the dark red product is obtained, which is 76%
of the theoretical yield. The crude product melts at 102-103°C.

Another modification of the Seyewetz method (applied also at St. Forts 1915-18)

is to use dilute nitric acid for the nitration, the process being carried out as follows.

A vessel of acid resistant bricks (2 m^3 capacity) is charged with 1500 kg of 26%

nitric acid (6 moles) heated to 20-30°C. An emulsion of 100 kg of phenol and

50 kg of water heated to 55-60°C is then introduced into the acid, which takes

about 8-10 min.

While this is being done and during the next operations the nitrator contents

are agitated by compressed air which enters through 4 pipes. During the mixing

of the reactants the temperature rises to 60°C and, after 15 min from the beginning

of the reaction, to 80°C. Should it rise higher than this, cold water must be added

and the flow of compressed air stopped until the temperature falls again to 80°C.

When it has stopped rising, i.e. when nitration has been completed, which usually
requires 45 min, air is blown through the reaction mixture until the temperature

goes down to 40°C. This takes about 12 hr. The dinitrophenol formed is either

skimmed off from the surface of the mixture by means of a sieve or filtered off on

a vacuum filter.

100 kg of phenol yields 155 kg of yellowish-orange coloured dinitrophenol,

which equals 80% of the theoretical yield. The melting point of the product ranges

between 101.5° and 105°C.

Nitration by this method has also been carried out in nitrators of smaller capac-

ity for batches of 18 kg of phenol and 155 kg of 26% nitric acid. Here the tem-

perature may be allowed to rise to 90-92°C. The yield and the purity of the product

obtained are as in the above processes.

The spent acid separated from dinitrophenol contains:

HNO 3 11-12%

HNO 2 0.02-0.03%

oxalic acid 1.5%

dinitrophenol 0.4-0.5%

It is used as a spray in towers for the recovery of the nitrogen oxides evolving during

the nitration of phenol to dinitrophenol. As a result of this operation the HNO 3
content in the acid rises to 19-20%.

A part of this acid is mixed with concentrated nitric acid (sp. gr. 1.40-1.50)

to obtain the 26% acid to be used for nitration again. The rest is transferred to

a distillation unit for concentration.

Purification of dinitrophenol

The product prepared by the above methods usually contains:

2,4-dinitiophenol 88-89%

2,6-dinitrophenol 34%

p- nitrophenol 0-4%

picric acid 3-5%