Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1999-02-26
2000-10-17
Lambkin, Deborah C.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
546152, C07D21172, C07D21500
Patent
active
061334480
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a new nitration system, and a new method for nitration of aromatic compounds.
Aromatic nitro compounds are of great importance, both as such and as starting material for the production of pharmaceuticals, dyestuff, pesticides and other important products. It is therefore of general interest both to optimise the existing nitration methods and to invent new ones.
Nitration of aromatic compounds is mainly performed by the use of a mixture of nitric and sulphuric acid (the "mixed acid" method) or by the use of nitric acid itself. For many aromatic compounds a satisfactory yield is obtained by the use of these comparatively cheap reagents. However, the use of strong acids makes these methods less suitable for the nitration of compounds containing acid sensitive groups. Furthermore, the nitration of several aromatic compounds gives only low or no yields by these reagents, This is the case for several hetero aromatic substance classes, for instance for pyridine and substituted pyridines.
Another system reported for the nitration of aromatic compounds is dinitrogen pentaoxide (N.sub.2 O.sub.5) dissolved in HNO.sub.3 (U.S. Pat. No. H-447 and DE-2435651). Dinitrogen pentaoxide has gained technical importance after the invention of new methods for its production (EP-295878, U.S. Pat. No. 4,432,902 and U.S. Pat. No. 4,525,252). Dinitrogen pentaoxide in HNO.sub.3 is more reactive than nitric acid or nitric acid/sulfuric acid. Less reactive aromatic compounds may therefore be successfully nitrated by this system. However, the presence of nitric acid may be detrimental to acid sensitive compounds. Furthermore, several compounds, for instance pyridine and substituted pyridines, are nitrated in very low yields even by this system (J. Bakke and I. Hegbom, Acta Chem. Scand., 48 (1994) 181).
Pyridine and several substituted pyridines are nitrated in yields lower than 5% by the methods referred to above. In our Norwegian Patent NO-C-174 462 the inventors described a method for nitration of aromatic compounds by using dinitrogen pentaoxide in sulphur dioxide (SO.sub.2). This method was particularly advantageous for pyridine systems. Good yields were obtained for a series of these compounds. However, the use of sulphur dioxide, especially as a solvent, has several disadvantages such as low reaction temperatures and technical difficulties in handling large amounts of liquid sulphur dioxide. The inventors later found that it was not necessary to use liquid sulphur dioxide as a solvent for the successful outcome of the reaction. Conventional organic solvents could be used together with only a minor proportion of sulphur dioxide. The experiments showed that approximately two molecules of sulphur dioxide per molecule of pyridine were needed in the reaction mixture to obtain as good results as those obtained when liquid sulphur dioxide was used for the reaction (NO-A-950367). Even though, Norwegian patent application no. 950367 discloses a nitration system advantageous over the one disclosed in Norwegian patent no. 174462, it still involves a need of some sulphur dioxide. By using modern equipment application of sulphur dioxide can be made safe. However, using sulphur dioxide makes the operations cumbersome.
Thus, the main object of this invention is to provide a nitration system and a method for nitration of aromatic compounds, in particular pyridine and substituted pyridines, where the disadvantages by using sulphur dioxide together with an organic solvent, are omitted.
This and other objects of the invention are solved as characterised by the features stated in the attached claims.
The inventors have found that the presence of sulphur dioxide in the reaction mixture containing the pyridine compound and dinitrogen pentaoxide is not necessary for the formation of a nitrated pyridine compound. Instead, the reaction between the pyridine compound and dinitrogen pentaoxide can be carried out in a standard organic solvent, for instance tetrahydrofuran (THF), nitromethane (CH.sub.3 NO.sub.2) or one of the other so
REFERENCES:
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patent: 5945537 (1999-08-01), Sikkema
Arnestad et al., "Direct Nitration of Pyridine and Substituted Pyridine", Acta Chemica Scandinavica, vol. 50, Jun. 1996, pp. 556-557.
Bakke et al., "Nitration of pyridine by dinitrogen pentaoxide in sulfur dioxide: investigation of the reaction mechanism", J. Chem. Soc. Perkin Trans, vol. 2, 1995, pp. 1211-1215.
Bakke et al., "Dinitrogen Pentoxide-Sulfur Dioxide, a New Nitration System", Acta Chemica Scandinavica, vol. 48, 1994, pp. 181-182.
Taylor, "Nitration of Biphenyl by Nitronium Borofluoride", Tetrahedron Letters, vol. 49, 1966, pp. 6093-6095.
Chemical Abstracts, vol. 91, No. 13, Sep. 24, 1979, (Columbus, Ohio, USA), p. 584, The Abstract No. 107978f, SU, 662551 A, (Gidaspov B.V. et al.) May 15, 1979.
Zielinska et al., "Reaction of Dinitrogen Pentoxide with Fluoranthene" J. Am. Chem. Soc., vol. 108, 1986, pp. 4126-4132.
Albright, et al., "Recent Laboratory and Industrial Developments", American Chemical Society, Nitration, Jun. 18, 1996, pp. 134-150.
Bakke Jan
Ranes Eli
Lambkin Deborah C.
Norsk Hydro ASA
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