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NITRO DERIVATIVES OF BENZENE^249

All the isomers are crystalline, pale yellow products and are poisonous. In

addition, sym-trinitrobenzene causes severe irritation of the skin. 1,3,5-Trinitro-
benzene can be formed in poor yield by the action of a mixture of anhydrous nitric

acid and fuming sulphuric acid on m- dinitrobenzene, the 1,2,4-isomer also being

formed in a very small quantity. The 1,2,3-isomer can be obtained only by indirect

methods.
sym-Trinitrobenzene, though the most readily obtainable as well as chemi-

cally the most stable of the three isomers, has not found practical application,

although it is a powerful explosive, with an explosive power slightly higher than

that of TNT. Its preparation is too expensive. In the organic chemical industry

sym-trinitrobenzene is used only for the manufacture of certain intermediates.

e.g. phloroglucinol.

PHYSICAL PROPERTIES OF SYM-TRINITROBENZENE

According to Jefremov and Bogoyavlenskii [37] sym-trinitrobenzene exists in

two isomorphic forms, which melt at 122.5°C and 106.3°C respectively.

It forms eutectics with other high nitrated aromatic compounds and certain

nitric esters (Table 40). (See also Burkhardt [65].)

The solubility of sym-trinitrobenzene in various solvents according to Orlova

[3] is given in Table 41.

The solubility of sym-trinitrobenzene in sulphuric acid of various concentrations

is given in Table 42 (according to Orlova [3]).

CHEMICAL PROPERTIES OF SYM-TRINITROBENZENE

Reactions with alkalis. sym-Trinitrobenzene like other polynitro-compounds.

exhibits high resistance to acids, while it reacts readily with alkalis.

It was Hepp [30] in 1882 who first found that sym-trinitrobenzene forms a dark

coloured substance with sodium alcoholate. V. Meyer [38] isolated a similar sub-

stance in 1896 when treating sym-trinitrobenzene with potassium alcoholate, and

assigned the following structure to it:

However, the formula could not be accepted, as, according to observations of

de Bruyn [16] in 1895, the product is formed only in the presence of alcohol, and

its empirical formula is C 6 H 3 (NO 2 ) 3 .CH 3 OK.

Angeli [39] suggested in 1884 that the addition of potassium alcoholate occurs

through one of the nitro groups: