The Purification of TNT

The purification of TNT, while in reality a part of its manufacture, may consist of any one of a number of methods, most of which are equally good as a means of extracting the impurities in the TNT. There are appearing every day new methods of purifying this substance, and the number is now too great to treat each method separately. It is thought wise, in view of the fact that a differentiation is made between crude and purified TNT, to treat the purification as a separate subject, rather than to include it in the discussion of the manufacture. 

The product which results from the application of the various processes outhned in the previous chapter is known as crude TNT. To define the word crude as applied to TNT is rather difficult, since a crude product is generally thought of as being a product that is contaminated with foreign substances. The purified product differs from the crude product in that these foreign matters are removed. As a matter of fact, crude TNT contains no real impurities, in the true sense of the word, because the impurities have been removed in the washing of the crude product. There are, it is true, other compounds of nitric acid and toluene (the lower nitration products), in the TNT, and 

The Purification by Alcohol. The crude TNT is placed upon the filter medium of a vacuum filter. An amount of 180 proof alcohol, equal in weight to one-quarter the weight of the TNT, is added. This mixture of TNT and alcohol is then agitated thoroughly, and fresh alcohol, equal to one-half the weight of the TNT is poured in on top of the mixtme. The filter prnnp is then started, and the alcohol is filtered off until the top level of the alcohol layer is coincident 

The action of the first portion of alcohol added is to dissolve the mononitrotoluenes and the dinitro-toluenes. The second volume added dilutes this solution and dissolves any of the nitrotoluenes which escaped solution by the previous addition. The last portion of alcohol serves to dissolve out any remaining traces of the impurities, and also serves to wash the TNT. 

The cost of this method of purif5dng TNT is rather high. Pure ethyl alcohol is preferable to denatured alcohol, because of the action the denaturing agents have on the TNT. The cost of the xmdenatured solvent is too high, however, to permit its use unless a well-developed plan of solvent recovery is in operation, so that practically none of the solvent is lost. 

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In the purification of TNT the following impurities have to be removed (1) traces of nitric and sulfuric acids (2) unsymmetrical isomers (3) products of incomplete nitration (4) byproducts (tetranitromethane, trinitrobenzene, nitrobenzoic acids, nitrocresols, etc)... 

The purification of TNT to remove DNT and other exudation-causing impurities increased the brittleness of TNT-based cast expls. However, since DNT was known to be an effective plasticizer of NC in propint formulations, it was found that Octol + 0.45% plasticized high viscosity NC and Octol +... 

Mononitrodiazotoluenesulfonic Acid, CH3. C6H2(N02).(N20).S02 mw 243.21, N 17.28% 6-Nitro-4-diazotoluene-2-sulfonic Acid, dk-red crysts, mp deflgr when heated mod sol in w si sol in ale prepd by treating 4-amino-2-sulfonic acid with cold fuming HNOj (Ref 1, p 567). Batik (Ref 2) found that this compd was formed on acidification of the waste waters from the purification of TNT with Na2SC>3 soln (Selllte Method). 

Pa. When a spent "sellite liquor from the purification of TNT(red water) was re-... 

Trinitrotoluol or Trotyl (TNT). TNT was manufd during WWII by a two-stage process, first to mononitrotoluene and then to TNT. The crude product was called Rohtri, mp 76— 78° and the purified TNT was called Reintri, mp 80—81°. There were several methods used to purify TNT, such as by Na sulfite soln or by re-crystn from nitric acid, in the opinion of Dr A. Stettbacher, the best method (but more expensive) was to recryst it from hot acet contg 8% benz. This method was used at the Schweiz-erische Sprengstoff-Fabrifc AG, Dottikon, and in Holland, for the purification of TNT used as a bursting charge in HE projectiles... 

Sulfite ion forms a complex of structure III (Refs 44 80), which is a source of yield loss during the purification of TNT if the pH exceeds 8. Cyanide ion also forms a compd of structure III (Ref 44) the kinetics of this reaction has been studied (Ref 76), TNT, as the anion I, can react with itself to form adducts of type II it can similarly react with 13 >5-trinitrobenzene (Ref 57). Primary and secondary aliphatic amines form a-complexes (Refs 46 58), but tertiary amines (in an aprotic solvent), and aromatic amines, form ir-complexes instead. Upon soln in liq ammonia, a complex of type III is initially formed, with no evidence of I (Ref 105). With time, a second NH2 group becomes attached to the ring carbon with the methyl group this compd has cis- and transisomers. Removal of the ammonia gave a red... 

The 5-(picrylmethyl) compd ( MPDM ) is formed to some extent during the purification of TNT (see Purification ) but the corresponding 3-isomer is not formed, probably because of greater steric hindrance of the reacting nitro group... 

A commonly used method of obtaining TNT is the direct nitrating of a mixture of the three isomers of nitrotoluene. Details are given later (Chapter IX) in the description of the manufacture of DNT and TNT. The purification of TNT from unsymmetrical derivatives of m- nitrotoluene consists as a rule in the sulphitation of di- or, more often, tri-nitrotoluenes or in crystallization of the trinitro-products. 

Recently, as the disposal of large volumes of toxic waste waters from the purification of TNT by sulphitation has. become a problem (p. 390), new ways are being sought for the manufacture of TNT free from the unsymmetrical isomers. Apart from the possibility, mentioned above, of the utilization of nitrotoluene obtained by nitrating toluene with a mixture of acetic anhydride and nitric acid, factories TNT are now tending to separate nitrotoluene isomers by methods similar to those applied in the manufacture of dyestuffs intermediates. 

Although the purification of TNT by sodium sulphite was widely used after World War I a number of factories continued with the crystallization method using among other solvents toluene, which directly after crystallization was used for nitration. 

Carbon Tetrachloride and Alcohol. A mixture of carbon tetrachloride and alcohol exerts a marked solvent action on the two lower nitro-compounds of toluene, and this action forms the basis of a patent granted for the purification of TNT. The proportions of the solvent used vary, certain conditions requiring particular concentrations of the two solvents. For the use of this solvent an especially designed filter is needed which wiU allow the mixture of TNT and the solvent to be thoroughly agitated directly on the filter medium. The method of operation is practically the same as that used for the purification by alcohol alone. The vacuum filter is so arranged that when the last layer of solvent... 

Many other solvents may be used to accomplish the purification of TNT, The organic solvents such as toluene, acetone, etc., find an especially wide application. The method followed with these solvents may be either a simple heating of the mixture of TNT and solvent until the impurities dissolve, followed by cooling and crystalhzation of the TNT, or it may be a more elaborate scheme somewhat as outlined in method 1 above. Well-developed processes have been worked out for pxirifying TNT by solvent means using nitrobenzene and nitrotoluene as the solvents. The solvents may be purified for further use by distillation with steam. (2)... 

Also the purification of TNT by crystallization from the acids (see also Vol. I. p. 378) should be considered. It offers the advantage that acids used for crystallization are recycled and enter the production process. However, the inipurities present in the acid after crystallization are introduced into the nitrator which is a drawback of the method. 

The nitro groups in a portion of the TNT are the oxidizing agent. Small amounts of HNBB are formed by this reaction during the purification of TNT with alkaline sodium sulfrte. Air oxidation in the presence of base and copper sulfate is claimed to give yields as high as 82 percent. 

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