Oxidation of Primary Aromatic Amines under Irradiation with Ultrasound and/or Microwaves

Abstract

The oxidation of primary aromatic amines, p-methylaniline, p-ethylaniline and p-chloroaniline to the corresponding azo- and azoxy-compounds has been observed in ultrasound and/or microwaves systems. The individual irradiation of microwaves and its simultaneous irradiation with ultrasound obviously elevate the conversion of amines, as compared with the individual irradiation of ultrasound and the heating in a plain water bath. However, the formation of formamidine resulted in poor selectivity toward azo and azoxy products in the presence of dimethylformamide (DMF).

ACKNOWLEDGMENT

The authors acknowledge support from Cesare Buffa for the building of ultrasound device and from Markus Hoffman for embellishment of the text.

Notes

^a 2 mmol of amine, 4 mmol of KMnO₄, 25 ml of DMF, 5 ml of H₂O. MW: MLS-Ethos MW system; 1 min at 1000 W to heat the mixture to 95 °C and further irradiated for 19 min at 70 W to maintain this temperature. US: 20 kHz with a Pyrex® horn (Φ 15 mm), nominal power 50 W, reaction vessel standing in a water bath heated at 95 °C.