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Sodium hydride
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<h2 id="basic-properties-and-structure">Basic properties and structure</h2> <p>NaH is colorless, although samples generally appear grey. NaH is around 40% denser than Na (0.968 g/cm3). </p><p>NaH, like <a href="/facts/Lithium_hydride/uWCl2pST">LiH</a>, <a href="/facts/Potassium_hydride/NEp3Vbd7">KH</a>, <a href="/facts/Rubidium_hydride/37RvT8xV">RbH</a>, and <a href="/facts/Caesium_hydride/bKLfb2PL">CsH</a>, adopts the <a href="/facts/Sodium_chloride/MWcXl3Mb">NaCl</a> <a href="/facts/Crystal_structure/bJ4bCeHd">crystal structure</a>. In this motif, each Na+ ion is surrounded by six H− centers in an <a href="/facts/Octahedral_molecular_geometry/bNXLVvks">octahedral</a> geometry. The <a href="/facts/Ionic_radius/C3dwKrrB">ionic radii</a> of H− (146 pm in NaH) and F− (133 pm) are comparable, as judged by the Na−H and Na−F distances.<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p> <h3>"Inverse sodium hydride" (hydrogen sodide)</h3> <p>A very unusual situation occurs in a compound dubbed "inverse sodium hydride", which contains H+ and Na− ions. Na− is an <a href="/facts/Alkalide/6lw9cCFv">alkalide</a>, 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 <a href="/facts/Adamanzane/VEW7GP2a">[36]adamanzane</a>. This molecule irreversibly encapsulates the H+ and shields it from interaction with the alkalide Na−.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> 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.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> </p> <h2 id="preparation">Preparation</h2> <p>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. </p> 2 Na + H2 → 2 NaH <p>The resultant suspension of NaH in mineral oil is often directly used, such as in the production of <a href="/facts/Diborane/k7egwbPf">diborane</a>.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="applications-in-organic-synthesis">Applications in organic synthesis</h2> <h3>As a strong base</h3> <p>NaH is a base of wide scope and utility in organic chemistry.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> As a <a href="/facts/Superbase/HyFVR2U3">superbase</a>, it is capable of <a href="/facts/Deprotonating/SmUSh369">deprotonating</a> a range of even weak <a href="/facts/Br%25C3%25B8nsted_acid/bqxQnJoX">Brønsted acids</a> to give the corresponding sodium derivatives. Typical "easy" substrates contain O-H, N-H, S-H bonds, including <a href="/facts/Alcohol_(chemistry)/Y0SCTDkh">alcohols</a>, <a href="/facts/Phenol/ACJs5NIU">phenols</a>, <a href="/facts/Pyrazole/mNToRYlQ">pyrazoles</a>, and <a href="/facts/Thiol/VemKEDP9">thiols</a>. </p><p>NaH notably deprotonates carbon acids (i.e., C-H bonds) such as 1,3-<a href="/facts/Dicarbonyl/JbdbaftY">dicarbonyls</a> such as <a href="/facts/Malonic_ester/2SEFoMyk">malonic esters</a>. The resulting sodium derivatives can be alkylated. NaH is widely used to promote condensation reactions of carbonyl compounds via the <a href="/facts/Dieckmann_condensation/DDDayVRc">Dieckmann condensation</a>, <a href="/facts/Stobbe_condensation/XDXF7TMJ">Stobbe condensation</a>, <a href="/facts/Darzens_condensation/BRuYwrob">Darzens condensation</a>, and <a href="/facts/Claisen_condensation/XDXF7TMJ">Claisen condensation</a>. Other carbon acids susceptible to deprotonation by NaH include sulfonium salts and <a href="/facts/Dimethyl_sulfoxide/T4HSYfuC">DMSO</a>. NaH is used to make <a href="/facts/Sulfur/IK0amTfM">sulfur</a> <a href="/facts/Ylide/WcfsUPR7">ylides</a>, which in turn are used to convert <a href="/facts/Ketone/BqQXpLo4">ketones</a> into <a href="/facts/Epoxide/PLxRI7r1">epoxides</a>, as in the <a href="/facts/Johnson%25E2%2580%2593Corey%25E2%2580%2593Chaykovsky_reaction/a8L93tg6">Johnson–Corey–Chaykovsky reaction</a>. </p> <h3>As a reducing agent</h3> <p>NaH reduces certain main group compounds, but analogous reactivity is very rare in organic chemistry (<i>see below</i>).<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> Notably <a href="/facts/Boron_trifluoride/2qa0NIH8">boron trifluoride</a> reacts to give <a href="/facts/Diborane/k7egwbPf">diborane</a> and <a href="/facts/Sodium_fluoride/HHcvwK7s">sodium fluoride</a>:<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> 6 NaH + 2 BF3 → B2H6 + 6 NaF <p>Si–Si and S–S bonds in <a href="/facts/Disilane/bVesjWzR">disilanes</a> and <a href="/facts/Disulfide/eDx5Xtlg">disulfides</a> are also reduced. </p><p>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).<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h3>Hydrogen storage</h3> <p>Although not commercially significant sodium hydride has been proposed for hydrogen storage for use in <a href="/facts/Fuel_cell/UcMYnCW3">fuel cell</a> 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.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="practical-considerations">Practical considerations</h2> <p>Sodium hydride is sold as a mixture of 60% sodium hydride (w/w) in <a href="/facts/Mineral_oil/KjXl9BUo">mineral oil</a>. 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 <a href="/facts/Air-free_technique/pEW9wY6e">air-free techniques</a>. </p> <h2 id="safety">Safety</h2> <p>NaH can <a href="/facts/Pyrophoricity/1b8Sl2AJ">ignite spontaneously in air</a>. It also reacts vigorously with water or humid air to release <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, which is very flammable, and <a href="/facts/Sodium_hydroxide/xjtdYtq7">sodium hydroxide</a> (NaOH), a quite corrosive <a href="/facts/Base_(chemistry)/M9wA7qeM">base</a>. In practice, most sodium hydride is sold as a dispersion in <a href="/facts/Mineral_oil/KjXl9BUo">mineral oil</a>, which can be safely handled in air.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Although sodium hydride is widely used in <a href="/facts/Dimethylsulfoxide/T4HSYfuC">DMSO</a>, <a href="/facts/Dimethylformamide/wjI8UfB4">DMF</a> or <a href="/facts/Dimethylacetamide/X4VpNaPw">DMAc</a> for <a href="/facts/SN2_Reaction/0N06Ra0R">SN2 type reactions</a> there have been many cases of fires and/or explosions from such mixtures.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a><a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <h2 id="cited-sources">Cited sources</h2> <ul><li>Haynes, William M., ed. (2016). <i><a href="/facts/CRC_Handbook_of_Chemistry_and_Physics/qjxzC2Cu">CRC Handbook of Chemistry and Physics</a></i> (97th ed.). <a href="/facts/CRC_Press/duTuH4hz">CRC Press</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 9781498754293.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Wells, A.F. (1984). Structural Inorganic Chemistry, Oxford: Clarendon Press <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>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. <a href="http://simons.hec.utah.edu/papers/266.pdf" target="_blank">http://simons.hec.utah.edu/papers/266.pdf</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Rittmeyer, Peter; Wietelmann, Ulrich (2000-06-15), "Hydrides", in Wiley-VCH Verlag GmbH & Co. KGaA (ed.), Ullmann's Encyclopedia of Industrial Chemistry, Weinheim, Germany: Wiley-VCH Verlag GmbH & Co. KGaA, doi:10.1002/14356007.a13_199, ISBN 978-3-527-30673-2, retrieved 2023-11-21 <a href="978-3-527-30673-2" target="_blank">978-3-527-30673-2</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>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.For early examples of NaH acting as a hydride donor, see ref. [3] therein.[citation needed] <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4797714" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4797714</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5. <a href="/wiki/ISBN_(identifier)" target="_blank">/wiki/ISBN_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>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. <a href="https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/28890pp2.pdf" target="_blank">https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/28890pp2.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>"The Dow Chemical Company – Home". www.rohmhaas.com. <a href="http://www.rohmhaas.com/wcm/products/product_detail.page?display-mode=msds&product=1120734&application=1120208" target="_blank">http://www.rohmhaas.com/wcm/products/product_detail.page?display-mode=msds&product=1120734&application=1120208</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>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. <a href="https://doi.org/10.1021%2Facs.oprd.9b00276" target="_blank">https://doi.org/10.1021%2Facs.oprd.9b00276</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>UK Chemical Reaction Hazards Forum Archived 2011-10-06 at the Wayback Machine and references cited therein <a href="http://www.crhf.org.uk/incident101.html" target="_blank">http://www.crhf.org.uk/incident101.html</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> </ol>