|||||||||||||| US0051 18880A United States Patent (19) 11 Patent Number: 5,118,880 Beck et al. 45) Date of Patent: Jun. 2, 1992 54 METHOD OF PREPARING 2,934,571 4/1960 Bonetti............................ 568/939 X 2-BROMO-4,6-DINITROMESITYLENE 3,180,900 4/1965 Sparks ................................. 568/937 3,221,062 11/1965 Wright ............................ 568/940 X 75) Inventors: William A. Beck, Middletown; David P. Higley, Wilmington, both of Del.: OTHER PUBLICATIONS John R. Tyndall, Pisgah Forest, N.C. Urbanaski, T. "Chemistry and Technology of Explo 73) Assignee: E. I. Du Pont de Nemours & Co., sives" vol. 1, p. 413, 1964, Permagon Press. Wilmington, Del. Topochiev, A. V., "Nitration of Hydrocarbons and Other Organic Compounds', p. 158, 1959, Permagon 21) Appl. No.: 720,679 Press. 22 Filed: Jun. 25, 1991 Primary Examiner-John S. Maples 51) Int. C. ............................................ CO7C 205/12 Assistant Examiner-C. Sayala 52 U.S.C. .................................... 568/940; C 57) ABSTRACT (58) Field of Search ............... 568/939, 940, 937,924, A method of preparing 2-bromo-4,6-dinitromesitylene 568/927, 932,933,934,936 having only small amounts of impurities, by first mixing 56 References Cited fuming sulfuric acid with bromomesitylene, and then adding concentrated nitric acid. U.S. PATENT DOCUMENTS 2,314,212 3/1943 Hennion .......................... 568/940 X 10 Claims, No Drawings 5, 118,880 1. 2 tylene, to free these products from undesirable impuri METHOD OF PREPARING ties. 2-BROMO-4,6-DINITROMESITYLENE In contrast to previous attempts, considerably purer 2-bromo-4,6-dinitromesitylene may be prepared accord 1. FIELD OF THE INVENTION 5 ing to the methods of the present invention. This invention relates to a method of preparing 3. SUMMARY OF THE INVENTION bromodinitrocompounds. More particularly it pertains The instant invention pertains to a method of prepar to a method of preparing 2-bromo-4,6-dinitromesity ing 2-bromo-4,6-dinitromesitylene comprising the steps lene. 10 of: 2. BACKGROUND OF THE INVENTION (a) mixing fuming sulfuric acid with 2-bromomesity lene; and 2-bromo-4,6-dinitromesitylene may be used as a start (b) mixing nitric acid with the mixture of step (a). ing material to form a number of compounds, such as Preferably, in step (a), the 2-bromomesitylene is for example 2-perfluoroalkyl-4,6-diaminomesitylene, 15 added to the fuming sulfuric acid at a temperature lower which in turn may be used as one of the main constitu than 30° C. preferably between 10° C. and 20° C., with ents in polyamides, polyimides, urethanes, ureas, and vigorous stirring. the like. The nitric acid is preferably in the form of an aqueous 2-bromo-4,6-dinitromesitylene has been prepared so solution containing nitric acid in excess of 70% by far by reacting nitric acid or a mixture of fuming sulfu 20 weight, and more preferably at a concentration of sub ric and nitric acids with bromonesitylene. Such prepa stantially 90%. Preferably the temperature during nitra rations are shown for example in very old as well as tion is maintained in the range of 30-50 C., and more more recent references, such as "Fittig and Storer, Lie preferably in the range of 35-45 C. bigs Ann. Chem., 147, 1-11 (1868)", "Suessenguth, Lie 4. DETAILED DESCRIPTION OF THE bigs Ann. Chem., 215, 242-252 (1882)', and "Adams and 25 Miller, J. Anner. Chem. Soc., 62, 53-56 (1940).' INVENTION The following is translated from Fittig and Storer (p. The instant invention pertains to a method of prepar 8): "By pouring fuming nitric acid over bromomesity ing 2-bromo-4,6-dinitromesitylene. lene at ambient temperature and after short standing, it The preparation of 2-bromo-4,6-dinitromesitylene by is converted into the (title) compound, which through 30 reacting nitric acid or a mixture of nitric acid and fum washing with water and recrystallization with alcohol is ing sulfuric acid with bronomesitylene appears to be easily purified. It crystallizes in fine, colorless needles, simple, since there are only two places in the which dissolve little in cold alcohol, easier in hot alco bromomesitylene where hydrogen atoms may be easily hol, yet are much less soluble than the starting com replaced by nitro groups. However, in practice, this pound. Its melting point is 189-190° C. Under warm 35 reaction is considerably more complicated. ing, the compound develops a genuine musk smell.' As aforementioned, depending on how the reaction is conducted, a number of undesirable by-products, such as 2,4,6-trinitromesitylene, 2,4-dibronomesitylene, and Analysis: Calculated Found 2,4-dibromo-6-nitromesitylene, are formed, which are C9 108 37.37% 37.16% 40 difficult to distinguish and separate, since they seem to H9 9 3.11 3.29 have similar crystalline characteristics. The by-pro Br 80 27.68 27. ducts of these reactions may sometimes prove to be 2 NO2 92 1.84 catastrophic to polymers intended to be made from the 289 100.00 main product (dinitrocompound) after hydrogenation 45 (diamine), since monoamines will serve as chain termi This preparation appears to be simple and leading to nators, and triamines will serve as crosslinkers. Thus, a pure product, since there are only two positions in the expensive procedures, such as repeated crystallizations, aromatic ring of bromomesitylene, which are open for sublimations, and the like are needed for purifying the substitution by nitro groups. Simple elemental analysis, product and remove the undesirable impurities. indicates the reaction to be clean and straightforward. 50 In contrast to previous attempts, considerably purer However, more careful examination of this reaction 2-bromo-4,6-dinitromesitylene may be prepared accord reveals it to be considerably more complicated. ing to the method of the present invention. It was very Depending on how the reaction is conducted, a num unexpected to find out that if the sulfuric acid and the ber of undesirable by-products, such as 2,4,6-trini nitric acid are not mixed simultaneously with the tromesitylene, 2,4-dibromomesitylene, and 2,4- 55 bronomesitylene, but only the sulfuric acid is mixed dibromo-6-nitromesitylene, are formed. Some of these first with bromomesitylene, and the nitric acid is mixed by-products are extremely difficult to separate, because then, the reaction yields a considerably purer product. they cocrystallize with the desired product, even upon One would expect that free water might be the culprit repeated recrystallization from a variety of solvents. in the production of various by-products. By mixing These by-products may also prove to be catastrophic to 60 first the fuming sulfuric acid with the fuming nitric acid, polymers intended to be made from derivatives of the all the water coming along with the nitric acid is re main product (dinitro compounds) after hydrogenation acted with the free sulfur trioxide of the fuming sulfuric (diamines), since monoamine derivatives will serve as acid, and thus, this is the technique one would follow to chain terminators, and triamine derivatives will serve as assure absence of water, and purer product. However, crosslinkers. Thus, expensive procedures, such as re 65 as already mentioned, Applicants found that mixing first peated crystallizations, sublimations, and the like are the bromomesitylene with the fuming sulfuric acid and needed for purifying the products obtained in subse then adding the nitric acid, produces a considerably quent conversions of impure 2-bromo-4,6-dinitromesi purer product, which is not concurrent with the above 5,118,880 3 4. logic. Applicants may not provide any proven explana Upon addition of nitric acid, the benzenesulfonic acid tion on why this is so. Only pure speculations may be derivative may be attacked by nitronium ion at the made, such as for example, that sulfonation may occur carbon bearing the sulfonic acid group; a proton first with subsequent replacement of the sulfonic groups may be lost from the sulfonic acid group in the by nitro groups, and for some unclear reason this inter 5 resulting intermediate, then a molecule of sulfur feres with the production of undesirable products. trioxide may be lost, leaving a molecule of 2 Another speculation is that 2-bromomesitylene, when bromo-4-nitromesitylene; added to nitric acid or to a mixture of nitric and sulfuric The resulting 2-brono-4-nitromesitylene may be suf acids, undergoes a rapid bromine-transfer reaction to ficiently deactivated by the nitro group that it can form a significant portion of dibromomesitylene. This 10 not undergo the bromine transfer process, but in may occur as the major process when reaction condi stead may undergo nitration to form the final, de tions are not sufficiently severe to effect nitration to any sired product, 2-bromo-4,6-dinitromesitylene. considerable extent. When conditions are such as to The above schemes are of course extremely specula tive and should be considered as such with regard to effect nitration, the bromine transfer reaction appears to 15 this invention. occur competitively with nitration, to an extent such On the basis of the results from the experiments that undesirable quantities of 2,4-dibromo-6-nitromesi shown in the Examples, one may conclude that under tylene are found in the final product. This compound ordinary nitration conditions, using 90% fuming nitric may arise from formation of 2,4-dibromonesitylene by acid (Examples 1 and 2), 80% nitric acid (Example 3), bromine transfer, followed by nitration of the dibromo 20 or mixed (fuming nitric and sulfuric) acids (Example 4), compound. there occurs an unexpected disproportionation of 2 It may also be speculated that the bromine transfer bromonesitylene to form substantial quantities of mesit reaction and subsequent conversion to final products ylene and 2,4-dibromomesitylene.