Simple, Efficient and Green Synthesis of Oximes under Ultrasound Irradiation

The condensation of aldehydes and ketones with hydroxylamine hydrochloride gives oximes in 81-95 % yields in water and EtOH under ultrasound irradiation. Compared to conventional methods, the main advantages of the present procedure are milder reaction conditions, shorter reaction times and higher yields. The chemical applications of ultrasound, 'Sonochemistry', have become an exciting new field of research during the past decade and increasingly used in organic synthesis in recent years. This is because a large number of organic reactions can be carried out in higher yields, shorter reaction times and milder conditions under ultrasonic irradiation. 1 Ultrasonication can accelerate many reactions as well as condensation of aldehydes and ketones with hydroxylamine hydrochloride. This may be due to the fact that the power of ultrasound (20-100 kHz, >10 W/cm 2 ) uses the energy to create cavitations, which involve the formation, growth, and implosive collapse of microscopic bubbles in a liquid. These bubbles are generated when the 'negative' pressure during the rarefaction phase of the sound wave is sufficiently large to disrupt the liquid. The implosive collapse of the bubbles can locally produce extreme temperatures and pressures (5000 °C, 20 MPa) for very short times, because of compression of the gas phase inside the cavity. These hotspots can lead to irreversible changes such as the formation of excited states, bond breakage, and the genera- tion of radicals. 2