Ultrasound effects on photochemical reactions 2. A study of ultrasound effects on some monomolecular and bimolecular photochemical reactions

The ultrasound effect on two well-described photochemical reaction was studied. Ultrasound does not affect the initiated photoisomerization of 2-phenylindan-1,3-dione to 3-benzylidenephthalide in the case when any additive is present, which is a monomolecular process, but enhances the effect of quenchers on its photoisomerization, which is a bimolecular process. The photodimerization of acenaphthylene is considerably affected by simultaneous sonication, which results in different ratios of the stereoisomers in comparison with the silent process. Sonication appears to affect the first reaction by homogeneous distribution of the excited states, or intermediates and possibly by quenching the excited tripler state of the second reaction. Two new reactors were designed allowing simultaneous irradiation of the reaction mixture by UV light and ultrasonic waves. (C) 1998 Elsevier Science S.A. All rights reserved.