7. 水溶液中での有機合成反応における超音波の効果
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概要
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Recently, there is growing interest in synthetic organic reactions in water without any organic solvent, which reactions are environmentally-friendly in relation to today's environmental concerns. Water has many advantages in terms of cost, safety, simple operation, and environmental preservation compared to the use of organic solvents. We have been continuously investigating reductive dehalogenation of halogenated compounds with a Raney alloy in aqueous media. Much attention is focused on environmental pollution caused by chlorinated organic compounds such as polychlorobiphenyl (PCBs) because PCBs are hazardous and have half-life in the environment in the order of decades. In our work on dehalogenation of aromatic halides, we turned our attention to development of a convenient and practical method for the disposal of PCBs. We found that a Raney Ni-Al alloy is effective for the dechlorination of PCBs congeners in dilute aqueous alkaline solution, and that ultrasonication not only accelerates the reaction rate but also effects regioselectivity in the reduced products. That is to say, dechlorination of 4-chlorobiphenyl (1a) selectively occurred at 60℃ under ultrasonic irradiation to afford the biphenyl in about 80% yield. Without ultrasonic irradiation, unreacted la remained (ratio: 48%); furthermore, longer reaction time was required compared to the reaction under irradiation. On the other hand, we have also interest in development of a convenient and practical method for the synthesis of diamines, because the coupling reaction of imines is significant to obtain vicinal diamines in organic synthesis. For example, the vicinal diamines are extremely useful as ligands of metal catalysts in asymmetric hydrogenation of aromatic ketones. We also report here our significant finding that under ultrasonication, the reaction time is shortened and the formation of the coupling product is increased.
- 日本ソノケミストリー学会の論文