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460 CHEMISTRY AND TECHNOLOGY OF EXPLOSIVES

Both methods are merely of theoretical interest. A method reported by R. Boyer.

Spencer and Wright [26] is of greater practical importance. It is based on the reaction

of pyridine picrate with phosgene in which picryl chloride forms in theoretical

yield. The pyridine in the aqueous solution left after picryl chloride has been sepa-

rated is regenerated as picrate by treating the solution with picric acid. The picrate

is returned to the process. According to T. Urbanski, Kuboszek and Dworak [26a]

phosgene can be replaced by thionyl chloride. For industrial practice a method was

developed at Griesheim [12] consisting in the nitration of l-chloro-2,4-dinitrobenzene.

It was applied in Germany during World War I.

As Desvergnes [18] reports, nitration by this method was effected in the following

way: 100 parts of chlorodinitrobenzene were dissolved in 200 parts of 40%

oleum. A mixture of 400 parts of anhydrous sulphuric acid and 300 parts of 94%

nitric acid was added to the solution. The whole was heated to 150°C with

stirring, this temperature being maintained for 3 hr longer. After cooling the mixture

was left for crystallization, filtered and the product was washed with cold

water.

According to Desvergnes [18] and Frankland and F. H. Garner [24], chloro-

dinitrobenzene can be nitrated with a mixture containing less nitric acid and more

sulphuric acid. The resultant product is of higher purity and the yield is also higher.

Desvergnes suggests a mixture of 560 parts of sulphuric acid (100%) and 150

parts of nitric acid (93%) for the nitration of 100 parts of chlorodinitrobenzene

dissolved in 200 parts of 40% oleum at 150°C.

Frankland and Garner dissolved 100 parts of chlorodinitrobenzene in 750 parts

of sulphuric acid (100%) and added 125 parts of nitric acid (93%) to the solution.

As Desvergnes pointed out in a comparison of the three methods the third one

looks the best as can be seen from the following figures (Table 103):

TABLE 103

Method

Theoretical Melting point of

yield the product

% °C

Griesheim 55 65

Desvergnes 82.5 75.8

Frankland and F. H. Garner 85 76

Physical properties. Picryl chloride is only sparingly soluble in water: at 15°C

0.0178 parts and at 100°C 0.346 parts dissolve in 100 parts of water.

On dissolution in hot water picryl chloride undergoes partial hydrolysis, picric

acid being formed. Solubility data for picryl chloride in organic solvents are given
in Table 104.
Kast [28] reports the specific gravity of molten and then solidified picryl chloride
to be 1.76.