2-bromo-4,6-dinitromesitylene may be used as a starting material to form a number of compounds, such as for example 2-perfluoroalkyl-4,6-diaminomesitylene, which in turn may be used as one of the main constituents in polyamides, polyimides, urethanes, ureas, and the like.
2-bromo-4,6-dinitromesitylene has been prepared so far by reacting nitric acid or a mixture of fuming sulfuric and nitric acids with bromomesitylene. Such preparations are shown for example in very old as well as more recent references, such as "Fittig and Storer, Liebigs Ann. Chem., 147, 1-11 (1868)", "Suessenguth, Liebigs Ann. Chem., 215, 242-252 (1882)", and "Adams and Miller, J. Amer. Chem. Soc., 62, 53-56 (1940)."
The following is translated from Fittig and Storer (p. 8): "By pouring fuming nitric acid over bromomesitylene at ambient temperature and after short standing, it is converted into the (title) compound, which through washing with water and recrystallization with alcohol is easily purified. It crystallizes in fine, colorless needles, which dissolve little in cold alcohol, easier in hot alcohol, yet are much less soluble than the starting compound. Its melting point is 189.degree.-190.degree. C. Under warming, the compound develops a genuine musk smell."
______________________________________ Analysis: Calculated Found ______________________________________ C9 108 37.37% 37.16% H9 9 3.11 3.29 Br 80 27.68 27. 2 NO.sub.2 92 1.84 -- 289 100.00 ______________________________________
This preparation appears to be simple and leading to a pure product, since there are only two positions in the aromatic ring of bromomesitylene, which are open for substitution by nitro groups. Simple elemental analysis, indicates the reaction to be clean and straightforward. However, more careful examination of this reaction reveals it to be considerably more complicated.
Depending on how the reaction is conducted, a number of undesirable by-products, such as 2,4,6-trinitromesitylene, 2,4-dibromomesitylene, and 2,4-dibromo-6-nitromesitylene, are formed. Some of these by-products are extremely difficult to separate, because they cocrystallize with the desired product, even upon repeated recrystallization from a variety of solvents. These by-products may also prove to be catastrophic to polymers intended to be made from derivatives of the main product (dinitro compounds) after hydrogenation (diamines), since monoamine derivatives will serve as chain terminators, and triamine derivatives will serve as crosslinkers. Thus, expensive procedures, such as repeated crystallizations, sublimations, and the like are needed for purifying the products obtained in subsequent conversions of impure 2-bromo-4,6-dinitromesitylene, to free these products from undesirable impurities.
In contrast to previous attempts, considerably purer 2-bromo-4,6-dinitromesitylene may be prepared according to the methods of the present invention.