Sodium hydride

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Sodium hydride
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  Sodium cation, Page Module:Chem2/styles.css has no content.Na+
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  Hydrogen anion, Page Module:Chem2/styles.css has no content.H−
Names
IUPAC name
Sodium hydride
Identifiers
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3D model (JSmol)
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EC Number Page Template:Plainlist/styles.css has no content.
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UN number 1427
  • InChI=1S/Na.H ☒N
    Key: MPMYQQHEHYDOCL-UHFFFAOYSA-N ☒N
  • InChI=1/Na.H/q+1;-1
    Key: BZKBCQXYZZXSCO-UHFFFAOYAY
  • InChI=1S/Na.H/q+1;-1
    Key: BZKBCQXYZZXSCO-UHFFFAOYSA-N
  • [H-].[Na+]
Properties
NaH
Molar mass 23.998 g·mol−1
Appearance white or grey solid
Density 1.39 g/cm3[1]
Melting point 425 °C (797 °F; 698 K)[4] (decomposes)
Reacts with water[1]
Solubility insoluble in all solvents
Band gap 3.51 eV (predicted)[2]
1.470[3]
Structure
fcc (NaCl), cF8
Fm3m, No. 225
4
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Thermochemistry[1][5]
36.4 J·mol-1·K-1
40.0 J·mol-1·K-1
−56.3 kJ⋅mol−1
−33.5 kJ⋅mol−1
Hazards
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[citation needed]

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3
3
2
W
Flash point 185 °C (365 °F; 458 K)[4] (closed cup)
Related compounds
Other anions
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Other cations
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Template:Chembox Footer/trackingTemplate:Short description

Sodium hydride is the chemical compound with the empirical formula NaH. This alkali metal hydride is primarily used as a strong yet combustible base in organic synthesis. NaH is a saline (salt-like) hydride, composed of Page Module:Chem2/styles.css has no content.Na+ and Page Module:Chem2/styles.css has no content.H− ions, in contrast to molecular hydrides such as borane, silane, germane, ammonia, and methane. It is an ionic material that is insoluble in all solvents (other than molten sodium metal), consistent with the fact that Page Module:Chem2/styles.css has no content.H− ions do not exist in solution.

Basic properties and structure

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 Page Module:Chem2/styles.css has no content.Na+ ion is surrounded by six Page Module:Chem2/styles.css has no content.H− centers in an octahedral geometry. The ionic radii of Page Module:Chem2/styles.css has no content.H− (146 pm in NaH) and Page Module:Chem2/styles.css has no content.F− (133 pm) are comparable, as judged by the Page Module:Chem2/styles.css has no content.Na−H and Page Module:Chem2/styles.css has no content.Na−F distances.[6][page needed]

"Inverse sodium hydride" (hydrogen sodide)

A very unusual situation occurs in a compound dubbed "inverse sodium hydride", which contains Page Module:Chem2/styles.css has no content.H+ and Page Module:Chem2/styles.css has no content.Na− ions. Page Module:Chem2/styles.css has no content.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 Page Module:Chem2/styles.css has no content.H+ and shields it from interaction with the alkalide Page Module:Chem2/styles.css has no content.Na−.[7] 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.[8]

Preparation

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 Template:Cvt.

Page Module:Chem2/styles.css has no content.2 Na + H2 → 2 NaH

The resultant suspension of NaH in mineral oil is often directly used, such as in the production of diborane.[9]

Applications in organic synthesis

As a strong base

NaH is a base of wide scope and utility in organic chemistry.[10] 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.[citation needed]

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.[citation needed]

As a reducing agent

NaH reduces certain main group compounds, but analogous reactivity is very rare in organic chemistry.[11] Notably boron trifluoride reacts to give diborane and sodium fluoride:[12][page needed]

Page Module:Chem2/styles.css has no content.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 (Page Module:Chem2/styles.css has no content.NaH·MI, M = Li, Na).[13]

Hydrogen storage

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.[14]

Practical considerations

Sodium hydride is often 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. Reactions involving NaH usually require air-free techniques.[citation needed]

Safety

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,[citation needed] which can be safely handled in air.[citation needed] 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.[15]

References

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  1. ^ a b c Template:RubberBible97th
  2. ^ Page Module:Citation/CS1/styles.css has no content.Singh, S.; Eijt, S. W. H. (30 December 2008). "Hydrogen vacancies facilitate hydrogen transport kinetics in sodium hydride nanocrystallites". Physical Review B. 78 (22) 224110. Bibcode:2008PhRvB..78v4110S. doi:10.1103/PhysRevB.78.224110.
  3. ^ Page Module:Citation/CS1/styles.css has no content.Batsanov, Stepan S.; Ruchkin, Evgeny D.; Poroshina, Inga A. (2016). Refractive Indices of Solids. Springer. p. 35. ISBN 978-981-10-0797-2.
  4. ^ a b c Sigma-Aldrich Co., Sodium hydride (dry). Retrieved on January 2026.
  5. ^ Page Module:Citation/CS1/styles.css has no content.Zumdahl, Steven S. (2009). Chemical Principles 6th Ed. Houghton Mifflin Company. p. A23. ISBN 978-0-618-94690-7.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Wells, A. F. (1984). Structural inorganic chemistry (5th ed.). Oxford [Oxfordshire] : New York: Clarendon Press ; Oxford University Press. ISBN 978-0198553700.
  7. ^ Page Module:Citation/CS1/styles.css has no content.Redko, M. Y.; Vlassa, M.; Jackson, J. E.; Misiolek, A. W.; Huang, R. H.; Dye, J. L.; et al. (2002). ""Inverse Sodium Hydride": A Crystalline Salt that Contains H+
     and Na−
    ". J. Am. Chem. Soc. 124 (21): 5928–5929. doi:10.1021/ja025655+. PMID 12022811.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Sawicka, Agnieszka; Skurski, Piotr; Simons, Jack (2003). "Inverse Sodium Hydride: A Theoretical Study" (PDF). J. Am. Chem. Soc. 125 (13): 3954–3958. Bibcode:2003JAChS.125.3954S. doi:10.1021/ja021136v. PMID 12656631. Archived (PDF) from the original on 2013-02-09.
  9. ^ Script error: No such module "Template wrapper".
  10. ^ Page Module:Citation/CS1/styles.css has no content.Gawley, Robert E. (2001). "Sodium Hydride". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. Chichester ; New York: J. Wiley and Sons. doi:10.1002/047084289X.rs073. ISBN 9780471936237.
  11. ^ Page Module:Citation/CS1/styles.css has no content.Too, Pei Chui; Chan, Guo Hao; Tnay, Ya Lin; Hirao, Hajime; Chiba, Shunsuke (2016-03-07). "Hydride Reduction by a Sodium Hydride–Iodide Composite". Angewandte Chemie International Edition. 55 (11): 3719–3723. doi:10.1002/anie.201600305. ISSN 1521-3773. PMC 4797714. PMID 26878823.
  12. ^ Page Module:Citation/CS1/styles.css has no content.Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, ISBN 0-12-352651-5
  13. ^ Page Module:Citation/CS1/styles.css has no content.Ong, Derek Yiren; Tejo, Ciputra; Xu, Kai; Hirao, Hajime; Chiba, Shunsuke (2017-01-01). "Hydrodehalogenation of Haloarenes by a Sodium Hydride–Iodide Composite". Angewandte Chemie International Edition. 56 (7): 1840–1844. doi:10.1002/anie.201611495. hdl:10356/154861. ISSN 1521-3773. PMID 28071853.
  14. ^ Page Module:Citation/CS1/styles.css has no content.DiPietro, J. Philip; Skolnik, Edward G. (October 1999). "Analysis of the Sodium Hydride-based Hydrogen Storage System being developed by PowerBall Technologies, LLC" (PDF). US Department of Energy, Office of Power Technologies. Archived (PDF) from the original on 2006-12-13. Retrieved 2009-09-01.
  15. ^ Page Module:Citation/CS1/styles.css has no content.Yang, Qiang; Sheng, Min; Henkelis, James J.; Tu, Siyu; Wiensch, Eric; Zhang, Honglu; Zhang, Yiqun; Tucker, Craig; Ejeh, David E. (2019). "Explosion Hazards of Sodium Hydride in Dimethyl Sulfoxide, N,N-Dimethylformamide, and N,N-Dimethylacetamide". Organic Process Research & Development. 23 (10): 2210–2217. doi:10.1021/acs.oprd.9b00276.

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