No m-nitrotetryl is produced if pure dimethylaniline is used in the usual process for the manufacture of tetryl. The amount of this impurity in the usual process depends upon the amount of monomethylaniline which may be present. A large excess of sulfuric acid tends toward the production of m-nitro compounds, but a reduction in the amount of sulfuric acid is not feasible for this increases the amount of benzene-insoluble material. m-Nitro-tetryl reacts with water, as TNA does; the nitro group in the 3-po8ition is replaced by hydroxyl, and m-hydroxytetryl or 2,4,6-trinitro-3-methylnitraminophenol, yellow crystals (rom water, m.p. 183°, is formed. This substance resembles picric acid and forms explosive salts. ^^ readily soluble in water, and m-nitrotetryl is effectively removed from crude tetryl by boiling the finely powdered solid with water.
Crude tetryl commonly contains a small quantity of amor-phous-appearing, buff-colored material of high melting point which is insoluble in benzene. The amount of this material is increased by the presence of larger amounts of water in the nitrating acid. Michler and Pattinson found that tetramethyl-benzidine is produced when dimethylaniline is heated with concentrated sulfuric acid. The same material is evidently formed during the preparation of tetryl and gives rise to the three substances indicated below, which constitute the benzene-insoluble impurity.
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