Safer Sodium

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Science  01 Jul 2005:
Vol. 309, Issue 5731, pp. 21
DOI: 10.1126/science.309.5731.21d

Metallic sodium and potassium, as well as their alloys, are useful for their potency in chemical reduction reactions. However, their instability when exposed to oxygen is inconvenient, and their highly exothermic reaction with water is a severe fire hazard in the laboratory.

Dye et al.have addressed this problem by mixing the metals with silica gel. Liquid Na-K alloy combines with silica at room temperature, producing a black powder that remains air-sensitive but is easily handled under nitrogen. Heating the powder to 150°C (or heating a pure Na/silica mixture to 165°C) yields a new product, stable for months, that retains much of its reducing capacity even on exposure to dry oxygen. This so-called stage I powder can be packed in columns and used for reductions or dehalogenative couplings of eluted aromatics. Further heating of the Na-stage I powder to 400°C gives a slightly less powerful stage II reducing agent that can be handled in humid air and used for drying organic solvents or for controlled reaction with water to generate small quantities of hydrogen. Preliminary experiments suggest that stage II formation involves chemical decomposition of the silica to produce Na4Si4 particles. — JSY

J. Am. Chem. Soc. 10.1021/ja051786+ (2005).

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