Sodium hydride

NaH is colorless, although samples generally appear grey. NaH is around 40% denser than Na (0.968 g/cm³).

NaH, like LiH, KH, RbH, and CsH, adopts the NaCl crystal structure. In this motif, each Na⁺ ion is surrounded by six H⁻ centers in an octahedral geometry. The ionic radii of H⁻ (146 pm in NaH) and F⁻ (133 pm) are comparable, as judged by the Na−H and Na−F distances.Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press

A very unusual situation occurs in a compound dubbed "inverse sodium hydride", which contains H⁺ and Na⁻ ions. Na⁻ is an alkalide, and this compound differs from ordinary sodium hydride in having a much higher energy content due to the net displacement of two electrons from hydrogen to sodium. A derivative of this "inverse sodium hydride" arises in the presence of the base [3⁶]adamanzane. This molecule irreversibly encapsulates the H⁺ and shields it from interaction with the alkalide Na⁻.{{cite journal |title="Inverse Sodium Hydride": A Crystalline Salt that Contains H⁺ and Na⁻ |journal=J. Am. Chem. Soc. |year=2002 |volume=124 |issue=21 |pages=5928–5929 |doi=10.1021/ja025655+ |pmid=12022811 |last1=Redko |first1=M. Y. |last2=Vlassa |first2=M. |last3=Jackson |first3=J. E. |last4=Misiolek |first4=A. W. |last5=Huang |first5=R. H. |last6=Dye |first6=J. L. |display-authors=etal}} Theoretical work has suggested that even an unprotected protonated tertiary amine complexed with the sodium alkalide might be metastable under certain solvent conditions, though the barrier to reaction would be small and finding a suitable solvent might be difficult.{{cite journal |url=http://simons.hec.utah.edu/papers/266.pdf |title=Inverse Sodium Hydride: A Theoretical Study |journal=J. Am. Chem. Soc. |year=2003 |volume=125 |pages=3954–3958 |doi=10.1021/ja021136v |pmid=12656631 |issue=13 |last1=Sawicka |first1=Agnieszka |last2=Skurski |first2=Piotr |last3=Simons |first3=Jack |bibcode=2003JAChS.125.3954S |url-status=live |archive-url=https://web.archive.org/web/20130209002911/http://simons.hec.utah.edu/papers/266.pdf |archive-date=2013-02-09}}

Industrially, NaH is prepared by introducing molten sodium into mineral oil with hydrogen at atmospheric pressure and mixed vigorously at ~8000 rpm. The reaction is especially rapid at 250−300 °C.

:{{chem2|2 Na + H2 → 2 NaH}}

The resultant suspension of NaH in mineral oil is often directly used, such as in the production of diborane.{{Citation |last1=Rittmeyer |first1=Peter |title=Hydrides |date=2000-06-15 |url=https://onlinelibrary.wiley.com/doi/10.1002/14356007.a13_199 |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry |editor-last=Wiley-VCH Verlag GmbH & Co. KGaA |access-date=2023-11-21 |place=Weinheim, Germany |publisher=Wiley-VCH Verlag GmbH & Co. KGaA |language=en |doi=10.1002/14356007.a13_199 |isbn=978-3-527-30673-2 |last2=Wietelmann |first2=Ulrich|url-access=subscription }}

NaH is a base of wide scope and utility in organic chemistry.Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{doi|10.1002/047084289X}}. As a superbase, it is capable of deprotonating a range of even weak Brønsted acids to give the corresponding sodium derivatives. Typical "easy" substrates contain O-H, N-H, S-H bonds, including alcohols, phenols, pyrazoles, and thiols.

NaH notably deprotonates carbon acids (i.e., C-H bonds) such as 1,3-dicarbonyls such as malonic esters. The resulting sodium derivatives can be alkylated. NaH is widely used to promote condensation reactions of carbonyl compounds via the Dieckmann condensation, Stobbe condensation, Darzens condensation, and Claisen condensation. Other carbon acids susceptible to deprotonation by NaH include sulfonium salts and DMSO. NaH is used to make sulfur ylides, which in turn are used to convert ketones into epoxides, as in the Johnson–Corey–Chaykovsky reaction.

NaH reduces certain main group compounds, but analogous reactivity is very rare in organic chemistry (see below).{{cite journal|last1=Too|first1=Pei Chui|last2=Chan|first2=Guo Hao|last3=Tnay|first3=Ya Lin|last4=Hirao|first4=Hajime|last5=Chiba|first5=Shunsuke|date=2016-03-07|title=Hydride Reduction by a Sodium Hydride–Iodide Composite|journal=Angewandte Chemie International Edition|language=en|volume=55|issue=11|pages=3719–3723|doi=10.1002/anie.201600305|issn=1521-3773|pmc=4797714|pmid=26878823}}
For early examples of NaH acting as a hydride donor, see ref. [3] therein.{{citation needed|date=September 2021}} Notably boron trifluoride reacts to give diborane and sodium fluoride:Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. {{ISBN|0-12-352651-5}}.

:6 NaH + 2 BF₃ → B₂H₆ + 6 NaF

Si–Si and S–S bonds in disilanes and disulfides are also reduced.

A series of reduction reactions, including the hydrodecyanation of tertiary nitriles, reduction of imines to amines, and amides to aldehydes, can be effected by a composite reagent composed of sodium hydride and an alkali metal iodide (NaH⋅MI, M = Li, Na).{{cite journal|last1=Ong|first1=Derek Yiren|last2=Tejo|first2=Ciputra|last3=Xu|first3=Kai|last4=Hirao|first4=Hajime|last5=Chiba|first5=Shunsuke|date=2017-01-01|title=Hydrodehalogenation of Haloarenes by a Sodium Hydride–Iodide Composite|journal=Angewandte Chemie International Edition|volume=56|issue=7|language=en|pages=1840–1844|doi=10.1002/anie.201611495|pmid=28071853|hdl=10356/154861 |issn=1521-3773|hdl-access=free}}

Although not commercially significant sodium hydride has been proposed for hydrogen storage for use in fuel cell vehicles. In one experimental implementation, plastic pellets containing NaH are crushed in the presence of water to release the hydrogen. One challenge with this technology is the regeneration of NaH from the NaOH formed by hydrolysis.{{cite web |url= https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/28890pp2.pdf |title= Analysis of the Sodium Hydride-based Hydrogen Storage System being developed by PowerBall Technologies, LLC |author= DiPietro, J. Philip |author2= Skolnik, Edward G. |date= October 1999 |publisher= US Department of Energy, Office of Power Technologies |access-date= 2009-09-01 |url-status= live |archive-url= https://web.archive.org/web/20061213093231/http://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/28890pp2.pdf |archive-date= 2006-12-13}}

Sodium hydride is sold as a mixture of 60% sodium hydride (w/w) in mineral oil. Such a dispersion is safer to handle and weigh than pure NaH. The compound is often used in this form but the pure grey solid can be prepared by rinsing the commercial product with pentane or tetrahydrofuran, with care being taken because the waste solvent will contain traces of NaH and can ignite in air. Reactions involving NaH usually require air-free techniques.

NaH can ignite spontaneously in air. It also reacts vigorously with water or humid air to release hydrogen, which is very flammable, and sodium hydroxide (NaOH), a quite corrosive base. In practice, most sodium hydride is sold as a dispersion in mineral oil, which can be safely handled in air.{{cite web|url=http://www.rohmhaas.com/wcm/products/product_detail.page?display-mode=msds&product=1120734&application=1120208|title=The Dow Chemical Company – Home|website=www.rohmhaas.com}} Although sodium hydride is widely used in DMSO, DMF or DMAc for SN2 type reactions there have been many cases of fires and/or explosions from such mixtures.{{cite journal |doi=10.1021/acs.oprd.9b00276 |doi-access=free |title=Explosion Hazards of Sodium Hydride in Dimethyl Sulfoxide, N,N-Dimethylformamide, and N,N-Dimethylacetamide |year=2019 |last1=Yang |first1=Qiang |last2=Sheng |first2=Min |last3=Henkelis |first3=James J. |last4=Tu |first4=Siyu |last5=Wiensch |first5=Eric |last6=Zhang |first6=Honglu |last7=Zhang |first7=Yiqun |last8=Tucker |first8=Craig |last9=Ejeh |first9=David E. |journal=Organic Process Research & Development |volume=23 |issue=10 |pages=2210–2217 }}[http://www.crhf.org.uk/incident101.html UK Chemical Reaction Hazards Forum] {{Webarchive|url=https://web.archive.org/web/20111006011739/http://www.crhf.org.uk/incident101.html |date=2011-10-06}} and references cited therein

{{Reflist}}

• {{cite book | editor= Haynes, William M. | date = 2016| title = CRC Handbook of Chemistry and Physics | edition = 97th | publisher = CRC Press | isbn = 9781498754293}}

{{Sodium compounds}}

{{Hydrides by group}}

Category:Metal hydrides

Category:Reagents for organic chemistry

Category:Sodium compounds

Category:Superbases

Category:Rock salt crystal structure

Category:Semiconductor materials