Free Radical Decomposition of Nitroaromatics Using Ozone and Ultrasound.

[NNadir]

Nitroaromatics are key intermediates in a host of industrially industrial processes, including many for the manufacture pharmaceutical compounds, explosives, dyes, plastics and other products.

However the compounds have profound toxicological implications and contamination of the environment by them is a serious problem in many parts of the world.

A journal I sometimes read for pleasure is Industrial & Engineering Chemistry Research, a publication of the American Chemical Society, one of the premier scientific societies in the United States.

I collected some papers back in May of last year and just got around to reading some of them today and came across some very interesting work on the destruction of nitroaromatics in waste water: http://pubs.acs.org/doi/abs/10.1021/ie801566z?prevSearch=%255Btitle%253A%2Bsonolysis%2Bdegradation%255D&searchHistoryKey=">Ind. Eng. Chem. Res., 2009, 48 (12), pp 5578–5583.

Nitroaromatics are highly stable and refractory to conventional treatments,2–5 which makes the remediation of wastewater containing nitroaromatics difficult. Problems associated with traditional treatments of industrial wastewater containing nitroaromatics have prompted environmental engineers and scientists to search for innovative solutions. Recently, various chemical treatment processes were proposed as options for the removal of organic contaminants. One promising approach uses advanced oxidation processes (AOPs), which are generally based on the generation of highly reactive species such as hydroxyl radicals (^.OH), and have the advantages of being nonselective, leading to no secondary pollution, and being particularly effective in removing persistent and biorefractory pollutants from water.6,7 One AOP has been in use for over a decade for complete degradation of organic pollutants in environmental decontamination; the combination of ozonation and sonolysis US/O₃ has been applied for the treatment of aromatic compounds.7–10 US/O₃ is more efficient and uses less energy than either ozonation or sonolysis alone. When ozone is used alone under alkaline conditions, it is decomposed and generates very reactive free radicals, such as · OH, which is nonselective and much more powerful than molecular oxidants.11 When sonolysis is combined with the ozonation system, the additional thermal decomposition of O3 results primarily in increased production of the hydroxyl radical.8,9 Furthermore, the ultrasonic irradiation enhances the mass transfer and decomposition of O₃ and produces more ·OH for more efficient degradation.12,13

The paper has an interesting mechanistic discussion.

After two hours of treatment with ultrasound and ozone, the majority of the nitrotoluene is converted into butene diacids, acetic acid and oxalic acid. Benzoic acids of various forms and benzene itself seem to be intermediates.

The ultrasound works primarily through the physical chemistry of bubbles, allowing for greater dispersion and the formation of many hydroxy radicals.

Cool chemistry, I think, esoteric, but cool.