Alkali Metals Plus Silica Gel: Powerful Reducing Agents and Convenient Hydrogen Sources

摘要

Alkali metals absorbed into silica gel yield three types of loose black powders (M-SG) that are strong reducing agents.All react nearly quantitatively with water to form hydrogen.Liquid NaK alloys form air-sensitive powders at room temperature that can be converted at 150 deg C to a form that is sensitive to moisture but not to dry air.Slowly heating sodium and silica gel to 400 deg C yields a third type that can be handled in ambient air with only slow degradation by atmospheric moisture.These materials eliminate many hazards associated with pure alkali metals by providing easily handled reducing agents and hydrogen sources.In continuous-flow reactors,they could reductively protonate aromatics,dechlorinate alkyl and aryl halides,and desulfurize various compounds.