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OTHER NITRO DERIVATIVES OF PHENOLS 537

They are yellow substances, readily soluble in hot water, which dye animal fibres

and leather.

Only the 2,4-isomer is of practical importance as the one most easily available.

The 4,6-isomer cannot be obtained directly, though it may be prepared by the

nitration of diacetylresorcinol.

Since the nitration of resorcinol by the conventional method for phenols (i.e.

sulphonation followed by the action of nitric acid) yields a trinitro derivative, two

other methods for the preparation of dinitroresorcinol are possible, viz.: oxidation

of dinitrosorcsorcinol or nitration of resorcylic acid followed by decarboxylation.

According to Kostanecki and Feinstein [27], the following reactions take place

in the former process:

(4)

Hemmelmayer [28] presented the nitration of resorcylic acid and its subsequent

decarboxylation by the following reactions :

(5)

In practice the first process is applied, as it gives a higher yield of the product.

The nitrosation is effected in a well known way. A weak (2.75%) aqueous solu-

tion of one mole of resorcinol is acidified with 2 moles of sulphuric acid. The solu-

tion is cooled down to -2°C and a 10% aqueous solution of 2 moles of NaNO 2

is added, dropwise. Crystalline yellowish 2,4-dinitrosoresorcinol is precipitated

in theoretical yield. The precipitate is washed and separated in a centrifuge or on
a vacuum filter prior to oxidation. From dinitrosoresorcinol the divalent lead salt
of dinitrosoresorcinol may be prepared, having initiating properties.