which is theoretically possible and is indicated above for that reason, there is not more than a trace.23 During the trinitration a small amount of the a-TNT is oxidized to trinitro ben zoic acid, finally appearing in the finished product in the form of TNB, which, however, does no harm if it is present in small amount. At the same time some of the material is destructively oxidized and nitrated by the strong mixed acid to form tetranitromethane, which is driven off writh the steam during the subsequent boiling and causes annoyance by its lachrymatory properties and unpleasant taste. The product of the trinitration is separated from the spent acid while still molten, washed with boiling water until free from acid, and grained—<jr, after less washing with hot water, subjected to purification by means of sodium sulfite.
n 3,5-Dinitrotoluene, in which both nitro groups are meta to the methyl, is probably not formed during the dinitration, and 3- and «-TNT, namely 3,4,5- and 2,3,5-trinitrotoluene, are not found among the final products of the nitration of toluene.
In this country the crude TNT, separated from the wash water, is generally grained by running the liquid slowly onto the refrigerated surface of an iron vessel which surface is continually scraped by mechanical means. In France the material is allowed to cool slowly under water in broad and shallow wooden tubs, while it is stirred slowly with mechanically actuated wooden paddles. The cooling is slow, for the only loss of heat is by radiation. The French process yields larger and flatter crystals, flaky, often several millimeters in length. The crystallized crude TNT is of about the color of brown sugar and feels greasy to the touch. It consists of crystals of practically pure a-TNT coated with an oily (low-melting) mixture of and y-TNT, 2,4-dinitrotoluene, and possibly TNB and TNX. It is suitable for many uses as an explosive, but not for high-explosive shells. The oily mixture of impurities segregates in the shell, and sooner or later exudes through the thread by which the fuze is attached. The exudate is disagreeable but not particularly dangerous. The difficulty is that exudation leaves cavities within the mass of the charge, perhaps a central cavity under the booster which may cause the shell to fail to explode. There is also the possibility that the shock of setback across a cavity in the rear of the charge may cause the shell to explode prematurely while it is still within the barrel of the gun.
The impurities may be largely removed from the crude TNT, with a corresponding improvement in the melting point and appearance of the material, by washing the crystals with a solvent. On a plant scale, alcohol, benzene, solvent naphtha (mixed xylenes), carbon tetrachloride, and concentrated sulfuric acid have all been used. Among these, sulfuric acid removes dinitro-toluene most readily, and organic solvents the p- and y-TNT, but all of them dissolve away a portion of the a-TTiT with resulting loss. The material dissolved by the sulfuric acid is recovered
Figure 46. TNT Manufacturing Building, Showing Barricades and Safety
Chutes. (Courtesy E. I. du Pont de Nemours and Company, Inc.) for use again or going to the acid-recovery treatment. The principal products of the first stage are o- (b.p. 222.3°) and p-nitro-toluene (m.p. 51.9°) in relative amounts which vary somewhat according to the temperature at which the nitration is carried out. During the dinitration, the para compound yields only 2,4-dinitro-toluene (m.p. 70°), while the ortho yields the 2,4- and the 2,6-(m.p. 60.5°). Both these in the trinitration yield 2,4,6-trinitro-toluene or a-TNT. 2,4-Dinitrotoluene predominates in the product of the dinitration, and crude TNT generally contains a
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