Sodium hydride
Sodium cation, Na+ Hydrogen anion, H− | |
Names | |
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IUPAC name
Sodium hydride
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Identifiers | |
3D model (
JSmol ) |
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ChemSpider | |
ECHA InfoCard
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100.028.716 |
EC Number |
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PubChem CID
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UNII | |
CompTox Dashboard (EPA)
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Properties | |
NaH | |
Molar mass | 23.998 g/mol[1] |
Appearance | white or grey solid |
Density | 1.39 g/cm3[1] |
Melting point | 638 °C (1,180 °F; 911 K)(decomposes)[1] |
Reacts with water[1] | |
Solubility | insoluble in all solvents |
Band gap | 3.51 eV (predicted)[2] |
Refractive index (nD)
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1.470[3] |
Structure | |
fcc (NaCl), cF8 | |
Fm3m, No. 225 | |
a = 498 pm
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Formula units (Z)
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4 |
Octahedral (Na+) Octahedral (H−) | |
Thermochemistry[5][4] | |
Heat capacity (C)
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36.4 J/mol K |
Std molar
entropy (S⦵298) |
40.0 J·mol−1·K−1[4] |
Std enthalpy of (ΔfH⦵298)formation |
−56.3 kJ·mol−1 |
Gibbs free energy (ΔfG⦵)
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-33.5 kJ/mol |
Hazards | |
Occupational safety and health (OHS/OSH): | |
Main hazards
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highly corrosive, reacts violently with water or humid air. |
GHS labelling:[6] | |
Danger | |
H260 | |
NFPA 704 (fire diamond) | |
Flash point | combustible |
Safety data sheet (SDS) | External MSDS |
Related compounds | |
Other anions
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Sodium borohydride Sodium hydroxide |
Other cations
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Lithium hydride Potassium hydride Rubidium hydride Caesium hydride |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Sodium hydride is the
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 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.[8]
"Inverse sodium hydride" (hydrogen sodide)
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−.[9] 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.[10]
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 250−300 °C.
- 2 Na + H2 → 2 NaH
The resultant suspension of NaH in mineral oil is often directly used, such as in the production of diborane.[11]
Applications in organic synthesis
As a strong base
NaH is a base of wide scope and utility in organic chemistry..
NaH notably deprotonates carbon acids (i.e., C-H bonds) such as 1,3-
As a reducing agent
NaH reduces certain main group compounds, but analogous reactivity is very rare in organic chemistry (see below).[13] Notably boron trifluoride reacts to give diborane and sodium fluoride:[14]
- 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).[15]
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.[16]
Practical considerations
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.
Safety
NaH can
References
- ^ a b c d Haynes, p. 4.86
- .
- ISBN 978-981-10-0797-2.
- ^ ISBN 978-0-618-94690-7.
- ^ Haynes, p. 5.35
- ^ Index no. 001-002-00-4 of Annex VI, Part 3, to Regulation (EC) No 1272/2008 of the European Parliament and of the Council of 16 December 2008 on classification, labelling and packaging of substances and mixtures, amending and repealing Directives 67/548/EEC and 1999/45/EC, and amending Regulation (EC) No 1907/2006. OJEU L353, 31.12.2008, pp 1–1355 at p 340.
- ^ "New Environment Inc. – NFPA Chemicals". newenv.com. Archived from the original on 2016-08-27.
- ^ Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press
- PMID 12022811.
- (PDF) from the original on 2013-02-09.
- ISBN 978-3-527-30673-2, retrieved 2023-11-21
- .
- PMID 26878823.]
For early examples of NaH acting as a hydride donor, see ref. [3] therein.[citation needed - ISBN 0-12-352651-5.
- PMID 28071853.
- ^ 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.
- ^ "The Dow Chemical Company – Home". www.rohmhaas.com.
- .
- ^ UK Chemical Reaction Hazards Forum Archived 2011-10-06 at the Wayback Machine and references cited therein
Cited sources
- Haynes, William M., ed. (2016). ISBN 9781498754293.