Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2000-03-01
2001-06-05
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06242656
ABSTRACT:
This invention relates to the production of a mixture of isomers of dinitronaphthalene containing an increased proportion of 1,5-dinitronaphthalene (referred to below as 1,5-DNN) by the nitration of pure 1-nitronaphthalene or of a crude nitronaphthalene mixture. 1,5-Dinitronaphthalene is a key compound for the production of 1,5-diaminonaphthalene (referred to below as 1,5-NDA). This is, inter alia, the starting compound for the production of 1,5-diisocyanatonaphthalene (1,5-NDI, trade name Desmodur 15®). 1,5-NDI is used as the isocyanate component in polyurethanes.
The production of nitrated aromatics has been known for a long time (G. A. Olah et al., Nitration: Methods and Mechanisms, VCH, New York, 1989). For decades, corresponding nitroaromatics have been produced industrially by nitration using a mixture of sulfuric acid and nitric acid (so-called mixed acid or nitrating acid). Nowadays polynitrations, for example dinitrations, are mostly carried out on the large scale by a two-step nitration (Kirk-Othmer, Encyclopedia of Chemical Technology, 1981, Vol. 15 and Ullmann, Encyclopedia of Industrial Chemistry, 1991, Vol. A17, pages 411-455).
The nitration of naphthalene (Houben-Weyl, Methoden der Organischen Chemie, 1971, Vol. 10, pages 492-495) yields a mixture of the isomers 1-nitronaphthalene and 2-nitronaphthalene in the ratio of about 95:5. In the nitration of the isomerically pure 1-nitronaphthalene using a mixture of sulfuric acid and nitric acid, a mixture of 1,5- and 1,8-dinitronaphthalene in the ratio of about 1:2 is formed, in addition to about 5% of other isomers (for example, 1,6- and 1,7-DNN). The unfavourable selectivity of the reaction leads in the production of 1,5-DNN chiefly to a high and undesirable content of 1,8-DNN.
DE-A 11 50 965 reports the increase in the selectivity by a rapid and intensive mixing of 1-nitronaphthalene dissolved in sulfuric acid together with nitrating acid. A disadvantage of this process is the considerable quantity of sulfuric acid used as solvent, the working-up of which is very expensive and cost-intensive. In addition, considerable quantities of trinitrated products, which both significantly decrease the yield of 1,5-DNN and are to be considered critical as regards safety regulations, can be formed in this process—particularly in the adiabatic reaction procedure described in the above-mentioned prior art.
WO 94/19310 describes nitrations of nitroaromatics on aluminium silicates partially doped with heavy metal, so-called claycops, as solid catalyst, which deliver high yields of dinitrated products together with small quantities of trinitroaromatics. However, nitrations of 1-nitronaphthalene carried out by this process yield ratios of isomers similar to those in classical nitrations with mixed acid.
Nitrations with nitric acid in organic solvents, for example, dichloroethane, and azeotropic removal of the water of the reaction are described in DE-A 24 53 529. They deliver dinitronaphthalene in high yields, but without influencing the ratio of isomers.
The object, accordingly, was to find a process for producing a mixture of isomers of dinitronaphthalene containing a high proportion of 1,5-dinitronaphthalene by nitration of 1-nitronaphthalene, in which mixed or nitrating acid, which simply entails expensive working up, need not be used.
Surprisingly, it has now been found that a shift of the ratio of isomers towards 1,5-DNN is possible where solid, perfluorinated, strongly acidic ion exchangers are used as catalyst in the nitration of 1-nitronaphthalene. The reaction is carried out in an excess of nitric acid, which can be recovered on completion of the reaction and after concentration.
The invention therefore provides a process for producing a mixture of isomers of dinitronaphthalene by nitration of nitronaphthalene, wherein nitronaphthalene, optionally in an inert organic solvent, is reacted with 1 to 20 times the equivalent quantity, based on nitronaphthalene, of 50% to 100% nitric acid in the presence of a solid, perfluorinated, strongly acidic ion exchanger. 1 to 20 times the equivalent quantity corresponds, in the case e.g. of a 65% nitric acid, to 33 wt. % to 92 wt. %, based on the solution, and in the case of an 100% nitric acid, to 26 wt. % to 88 wt. %.
The mixtures of DNN isomers produced according to the invention contain a surprisingly high proportion of the 1,5-DNN isomer. Conventionally, the content of 1,5-DNN is more than 30 wt. %, in particular between 34 and 50 wt. %. The content of other secondary products, in particular of other isomers of dinitronaphthalene and of more highly nitrated products, is smaller than in comparable nitrations with mixed acid.
The starting product used can be pure 1-nitronaphthalene or even a crude nitronaphthalene mixture, such as is obtained as crude product in the nitration of naphthalene.
The solid, perfluorinated, strongly acidic ion exchanger catalyses the reaction to form the 1,5-dinitronaphthalene-enriched end product. Such perfluorinated, strongly acidic ion exchangers are known in prior art and are commercially available, for example, under the trade name Nafion®. Preferably an ion-exchange resin with the trade name Nafion® NR 50 Superacid Catalyst (Dupont) is used.
The ion exchanger used as catalyst is chemically inert and can be easily removed from the reaction batch, for example, by filtration. A working up, as in the case of the diluted and organically contaminated sulfuric acid which accumulates during nitrations with mixed acid (nitric acid/sulfuric acid mixture), is advantageously omitted in the process according to the invention.
The concentration of the nitric acid is between 50% and 100%, preferably between 60% and 80%. The quantity of nitric acid added is between 1 equivalent and 20 equivalents, based on the quantity of nitronaphthalene used. In the case of a 65% nitric acid, this corresponds to 33 to 92 wt. %. Preferably quantities of nitric acid of between 3 equivalents (in the case of 65% nitric acid: 62.7 wt. %) and 12 equivalents (corresponding to 87.0 wt. % of 65% nitric acid) are used.
The process is conventionally carried out at temperatures of between 20° C. and 100° C., preferably 80° C.
To ensure a complete reaction, the conversion is carried out with thorough mixing of the reaction mixture, for example, by intensive stirring for a reaction period of between 20 minutes and 8 hours, for example, 3 hours.
In the absence of additional solvent, the process according to the invention can only be carried out in an excess of nitric acid, or else optionally after the introduction of a solvent.
In this connection, the 1,5-selectivity can, surprisingly, be increased even further in the presence of an inert organic solvent.
The process according to the invention is therefore preferably carried out in the presence of an inert organic solvent. Suitable solvents of this kind are polar compounds which are inert in the reaction medium. Examples of such solvents are sulfolane or nitroalkanes, such as, for example, nitromethane.
The process according to the invention is preferably carried out in the presence of sulfolane as organic solvent.
Unreacted nitronaphthalene, excess nitric acid and solvent can be returned to the process.
The quantity of organic solvent added is between 0.1 and 20 parts and preferably between 0.5 and 3 parts, based on the quantity of nitronaphthalene used. The concentration of the nitric acid is adjusted according to the quantity of solvent added and is between 50% and 100%, preferably 60% to 80%.
The mixture of isomers of dinitronaphthalene can be separated into the isomeric dinitronaphthalenes in known manner, for example, by fractional crystallisation. Such separations of isomers, for example, with dimethylformamide or dichloroethane as solvent, have already been described (cf. Houben-Weyl, Methoden der organischen Chemie, 1971, Vol. 10, page 494).
The invention also provides mixtures of isomers consisting of 1,5- and 1,8-dinitronaphthalene, having a 1,5-dinitronaphthalene content of more than 30 wt. %, in particular of between 34 and 50 wt. %.
Steinlein Christian
Wegener Gerhard
Barts Samuel
Bayer Aktiengesellschaft
Gil Joseph C.
Whalen Lyndanne M.
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