Sodium Hydride

Introduction

Sodium hydride (NaH) [¹] is an important reagent for the synthesis of both organic and inorganic compounds. It is used as a base for the deprotonation of alcohols, phenols, amides, ketones, esters, and stannanes, and thus it is widely used to promote condensations of carbonyl compounds via the Dieckmann, Stobbe, Darzens and Claisen condensations. Under aprotic conditions NaH is an effective reducing agent for disulfides, disilanes, azides, and isoquinolines.

NaH is produced by the direct reaction of hydrogen and liquid sodium. Pure NaH is colorless (mp 800 ˚C), although samples generally appear grey, and commercially available either as free-flowing grey powder (95% dry hydride) or as grey powder dispersed in mineral oil. Because of its rapid and irreversible reaction with water, NaH can be used to dry some organic solvents. NaH-based hydrogen storage systems are also being developed for use in fuel-cell vehicles.

As sodium hydride can behave both as a base and a source of hydride, this dual ability in the presence of an electrophile and suitable solvents results in the formation of selective products. [²] An interesting selectivity between NaH and potassium hydride was observed in the preparation of Macroviracin A where NaH yielded the desired macro­cyclic dilactone core. [²]

References

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• 1c Wiberg E. Amberger E. Hydrides of the Elements of Main Groups I-IV   Elsevier; New York: 1971. 
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• 1e Gawley RE. Hennings DD. In Encyclopedia of Reagents for Organic Synthesis   John Wiley & Sons Ltd.; Chichester: 2006. 
• 1f DiPietro JP. Skolnik EG. Analysis of the Sodium Hydride-Based Hydrogen Storage System being developed by PowerBall Technologies LLC  US Department of Energy, Office of Power Technologies, 1999, 861-888
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