An Easy Access to Aromatic Azo Compounds under Ultrasound/Microwave Irradiation

Chemoselective reduction of nitroarenes to azo and azoxy compounds was easily achieved using zinc powder and ­ammonium chloride in DMF or DMF-water (95:5) under high intensity ultrasound (US) or microwave (MW) irradiation, separately or combined. When carried out under conventional heating the reaction required much higher temperatures and gave lower yields. The addition of a small amount of water caused a dramatic increase in the reactivity, permitting the reduction of hindered nitroarenes at the expense of selectivity. A novel reactor for combined US/MW ­irradiation was employed which demonstrated additional beneficial effects.