Sodium hydride 521877 223908287 2008-07-06T13:22:20Z 72.93.68.89 {{Chembox new | Name = Sodium hydride | ImageFile = Sodium-hydride-3D-vdW.png | ImageSize = 200px | ImageName = Sodium hydride | Section1 = {{Chembox Identifiers | CASNo = 7646-69-7 }} | Section2 = {{Chembox Properties | Formula = NaH | MolarMass = 23.99 g/mol | Appearance = colorless to gray solid | Density = 1.396 g/cm³, solid | Solubility = Reacts | MeltingPt = 800 °C with decomp. }} | Section3 = {{Chembox Structure | Structure = [[Cubic crystal system|fcc]] ([[Sodium chloride#Crystal structure|NaCl]]) }} | Section7 = {{Chembox Hazards | ExternalMSDS = [http://www.state.nj.us/health/eoh/rtkweb/1702.pdf External MSDS] | EUClass = Flammable ('''F''') | NFPA-H = 3 | NFPA-F = 3 | NFPA-R = 2 | NFPA-O = W | RPhrases = {{R15}} | SPhrases = {{S2}}, {{S7/8}}, {{S24/25}}, {{S43}} }} | Section8 = {{Chembox Related | OtherCations = [[Potassium hydride]] | OtherCpds = [[Sodium borohydride]] }} }} '''Sodium hydride''' is the [[chemical compound]] with the formula NaH. It is primarily used as a strong [[base (chemistry)|base]] in [[organic synthesis]]. NaH is representative of the saline hydrides, meaning it is a salt-like [[hydride]], composed of Na<sup>+</sup> and H<sup>−</sup> ions, in contrast to the more molecular hydrides such as [[borane]], [[methane]], [[ammonia]] and [[water]]. It is an ionic material that is insoluble in organic solvents (although apparently soluble in molten Na), consistent with the fact that H<sup>−</sup> remains an unknown anion in solution. Because of the insolubility of NaH, all reactions involving NaH occur at the surface of the solid. ==Basic properties and structure== NaH is produced by the direct reaction of hydrogen and liquid sodium.<ref name=Holl>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.</ref> Pure NaH is colorless, although samples generally appear gray. NaH is ca. 40% more dense than Na (0.968 g/cm³). NaH, like [[Lithium hydride|LiH]], [[Potassium hydride|KH]], [[Rubidium hydride|RbH]], and CsH, adopts the [[sodium chloride|NaCl]] [[crystal structure]]. In this motif, each Na<sup>+</sup> ion is surrounded by six H<sup>−</sup> centers in an octahedral geometry. The ionic radii of H<sup>−</sup> (146 pm in NaH) and F<sup>−</sup> (133 pm) are comparable, as judged by the Na−H and Na−F distances.<ref>Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press</ref> ==Applications in organic synthesis== ===As a strong base=== First and foremost, NaH is a base of wide scope and utility in organic chemistry.<ref>Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. DOI: 10.1002/047084289.</ref> 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 [[alcohol]]s, [[phenol]]s, [[pyrazole]]s, and [[thiol]]s. NaH most notably is employed to deprotonate carbon acids such as 1,3-dicarbonyls and analogues such as [[malonic ester]]s. 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 [[Dimethyl sulfoxide|DMSO]]. NaH is used to make [[sulfur]] [[ylide]]s, which in turn are used to convert [[ketones]] into [[epoxides]]. ===As a reducing agent=== NaH reduces certain main group compounds, but analogous reactivity is unknown in organic chemistry. Notably [[boron trifluoride]] reacts to give [[diborane]]:<ref name=Holl/> :6 NaH + 2 BF<sub>3</sub> → B<sub>2</sub>H<sub>6</sub> + 6 [[sodium fluoride|NaF]] Si-Si and S-S bonds in [[disilane]]s and [[disulfide]]s are also reduced. ===Drying agent=== Because of its rapid and irreversible reaction with water, NaH can be used to dry some organic solvents. Other drying agents are far more widely used, such as [[calcium hydride]]. ==Practical considerations== Sodium hydride is sold by many chemical suppliers such as [[Sigma-Aldrich]] and [[ACROS]], usually 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 pure white solid is prepared by rinsing the oil with pentane or THF, care being taken that the washings will contain traces of NaH that can ignite in air. Reactions involving NaH require an [[inert]] atmosphere, such as [[nitrogen]] gas. Typically NaH is used as a suspension in [[THF]], a solvent that resists deprotonation but solvates many organosodium compounds. ==Safety== NaH can ignite in air, especially upon contact with water to release [[hydrogen]], which is also flammable. Hydrolysis converts NaH into sodium hydroxide ([[NaOH]]), a [[caustic]] [[base (chemistry)|base]]. In practice, most sodium hydride is dispensed as a dispersion in oil, which can be safely handled in air. ==References== <references/> [[Category:Metal hydrides]] [[Category:Sodium compounds]] [[Category:Reagents for organic chemistry]] [[Category:Bases]] [[ar:هيدريد صوديوم]] [[ca:Hidrur de sodi]] [[de:Natriumhydrid]] [[fr:Hydrure de sodium]] [[it:Idruro di sodio]] [[nl:Natriumhydride]] [[ja:水素化ナトリウム]] [[pl:Wodorek sodu]] [[pt:Hidreto de sódio]] [[sv:Natriumhydrid]] [[zh:氢化钠]]