urbaf2

492 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Constituents

Picric acid with α− benzylnaphthalene

α− chloronaphthalene

α− bromonaphthalene

α− nitronaphthalene

β− chloronaphthalene

acenaphthene

phenanthrene

M. p., °C

97.0

125.7

35.0

about 55 (non

uniform melting)

81.5

160.8

132.8

retene 120.9

With amines, picric acid yields picrates. Some of them such as quinine or qul-

noline picrates, are very difficult to dissolve in water and this may be utilized for

quantitative determination of picric acid or these bases.

The composition of various practically applied eutectics given by picric acid

is discussed in the chapter on fusible explosive compositions in Vol. III.

For the qualitative determination of picric acid a characteristic reaction with

potassium cyanide may be utilized. When an aqueous solution of the two compounds

is boiled a red-coloured potassium salt of “isopurpuric acid” is formed. Formula

I was assigned to this compound by Nietzki and Petri [54], while Borsche and Böcker

[55] suggested the formulae IIa or IIb.

I IIa IIb

However, Lobry de Bruyn [56] demonstrated that “isopurpuric acid” is a mixture

of compounds in which one of the nitro groups has been reduced to an azoxy-,

azo-, or nitroso group, while the cyano groups have entered the ring, replacing

a hydrogen atom or a nitro group.

Picric acid is not resistant to strong oxidizing agents. It is oxidized by boiling

nitric acid to yield oxalic acid. Boiling with ammonium persulphate results in

a complete oxidation, according to the equation:

C 6 H 2 (NO 2 ) 3 OH

(NH 4 ) 2 S 2 O 8

CO 2 + HNO 3 + HCN (6)

When mildly reduced, for example with sodium sulphide or hydrosulphite or
with ferrous sulphate, picric acid is converted into picramic acid, a very useful

intermediate in the dyestuffs industry and a starting material for the preparation

of dinitrodiazophenol, a primary explosive (Vol. III). Stronger reduction may lead

to the formation of triaminophenol.