Sonochemical Degradation Reactions of Nitrobenzene: Oxidation, Reduction, and Dimerization

摘要

Nitroaromatic compounds with energetic characteristics are frequently present in waste streams produced at U.S. Army facilities. Previous work on the sonolytic destruction of nitroaromatic species in aqueous solutions involved primarily denitration together with oxidation via hydroxyl radical attack. Subjecting a chemical reaction to ultrasound, with frequencies roughly between 15 kHz and 10 MHz, can have a drastic effect. Ultrasound causes acoustic cavitation - the creation, growth, and collapse of bubbles in the solution. The collapse produces localized spots of extreme conditions including temperatures as high as 5000 K and pressures near 1000 atmospheres. The extreme conditions thus created initiate three distinct destruction pathways for organic contaminants: oxidation by hydroxyl radicals, supercritical water oxidation, and pyrolysis. These three mechanisms account for the degradation mechanisms for organic species in water. Interest in ultrasound for decontamination arises from its ability to cause these effects relatively inexpensively, with simple equipment and without severe experimental conditions. In this report, a simple mechanical manipulation of the experimental apparatus is shown to greatly alter the degradation pathway to promote reduction of the nitro group rather than oxidation of the aromatic ring. This work describes this experimental change and demonstrates the sonochemical reduction of nitrobenzene.