Efficient degassing of dissolved oxygen in aqueous media by microwave irradiation and the effect of microwaves on a reaction catalyzed by Wilkinson's catalyst

• Degassing dissolved oxygen in water was enhanced when using microwave heating.
• Degassing was more effective with lower frequency microwaves.
• Synthesis of cyclohexanol with Wilkinson's catalyst was investigated under microwave irradiation.

To the extent that some reactions are oxygen-sensitive, we herein examined the degassing of dissolved oxygen in water and in 2-propanol solvent by microwave heating with regard to the effects of the microwave frequency (2.45 GHz versus 915 MHz), and with regard to when samples are subjected to electric-field-rich and magnetic-field rich 2.45-GHz microwaves. Changes in the quantity of dissolved oxygen were ascertained by monitoring its concentration in such solvents when exposed to microwave and conventional heating using a polarographic technique and by the chemical oxygen demand (COD) method. The specific microwave (non-thermal) effect played a role in the degassing process on comparing results between microwave heating and conventional heating under identical temperature conditions. The 915-MHz microwaves were more effective, at least at 60 °C, owing to their greater penetration into the solutions. No significant differences were found when degassing was carried out on exposing the water sample to 2.45-GHz microwaves with the sample located within the waveguide at positions rich in either the electric field or the magnetic field (T=80 °C). Conversion of cyclohexanone to cyclohexanol via hydrogen transfer in the presence of Wilkinson's catalyst and 2-propanol solvent (hydrogen source) was also investigated to assess the effect(s) that microwaves might have on this oxygen-sensitive reaction with respect to product yields in contrast to conventional heating by the oil-bath method.