Chemikalen.de English: Explosively Green Chemistry

A new approach to polynitration could make the manufacture of explosives a greener process.

Aromatic nitration is a nightmare reaction in terms of its environmental credentials. It is a key procedure in research and industrial chemistry. But the standard methods carry with them a high penalty in terms of the large volumes of strong acid needed and the equally large volumes of waste products formed. Innovative solid catalysts and the use of dinitrogen pentoxide have helped clean up the manufacturing process but there are still problems when it comes to polynitration for explosives production.

Now, Michael Crampton, and colleagues Emma Cropper, Linda Gibbons and Ross Millar of the University of Durham with support from the Corporate Research Portfolio of the Defence Evaluation and Research Agency (DERA) have taken the bold step of using perfluorocarbons in polynitration in order to improve the reactions’ environmental profile. They have obtained very good yields of polynitroaromatics using much smaller quantities of hazardous mineral acids than are currently employed. Moreover, the perfluorocarbons can readily be recycled, so greatly reducing waste.

According to Crampton and his team, the perfluorocarbons act as both solvent and as bulking agents in the reactions of various aromatic compounds including toluene, benzene, phenol, benzyl chloride and chlorobenzene. Either nitric acid or dinitrogen pentoxide can be used to generate highly nitrated products but without the need for the large quantities required in the conventional scheme. The researchers point out that the reactions can be carried out in just one step and at lower temperature.

Crampton is quick to point out that perfluorocarbons are not ozone depleters like their chloro cousins and are chemically inert and immiscible with most organic solvents and aqueous media, so endowing them with facile recyclability once the reaction is over. Indeed, the team found that straight recycling without further purification gave the same effective results on the second pass. For instance, they were able to produce trinitrotoluene (TNT) at 70 °C with five equivalents of nitric and sulfuric acid. Products are quickly separated out using water.

Anonymous…Quelle: Alchemist/USA; Michael R. Crampton, Emma L. Cropper, Linda M. Gibbons & Ross W. Millar. The nitration of arenes in perfluorocarbon solvents. Green Chem 2002