Lithium aluminium hydride: Difference between revisions

| Watchedfields =dkmrodkrg

| verifiedrevid = 457117309

| Name = Lithium aluminium hydride

| ImageFile =

| ImageFileL1 = lithium aluminium hydride.svg

| ImageNameL1 = Wireframe model of lithium aluminium hydride

| ImageFileR1 = Lithium-aluminium-hydride-layer-3D-balls.png

| ImageNameR1 = Unit cell ball and stick model of lithium aluminium hydride

| ImageFile2 = Lithium aluminium hydride.jpg

| ImageName2 = Lithium aluminium hydride

| ImageSize2 =

| PIN = Lithium tetrahydridoaluminate(III)

| SystematicName = Lithium alumanuide

| OtherNames = {{ubl|Lithium aluminium hydride|Lithal|Lithium alanate|Lithium aluminohydride|Lithium tetrahydridoaluminate}}

| IUPACName =

| Section1 = {{Chembox Identifiers

| Abbreviations = LAH

| InChI = 1S/Al.Li.4H/q-1;+1;;;;

| CASNo_Ref = {{cascite|correct|CAS}}

| CASNo1_Ref = {{cascite|correct|??}}

| CASNo1 = 14128-54-2

| CASNo1_Comment = (²H₄)

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = 77UJC875H4

| PubChem = 28112

| PubChem1 = 11062293

| PubChem1_Comment = (²H₄)

| PubChem2 = 11094533

| PubChem2_Comment = (³H₄)

| ChemSpiderID = 26150

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| EINECS = 240-877-9

| ChEBI_Ref = {{ebicite|correct|EBI}}

| RTECS = BD0100000

| SMILES = [Li+].[AlH4-]

| StdInChI_Ref = {{stdinchicite|correct|chemspider}}

| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

| Gmelin = 13167

| UNNumber = 1410

}}

| Section2 = {{Chembox Properties

| Formula = {{chem2|Li[AlH4]}}

| Li=1|Al=1|H=4

| Appearance = white crystals (pure samples)<br />grey powder (commercial material) <br /> [[hygroscopic]]

| Odor = odorless

| Solubility = Reacts

| Solvent1 = tetrahydrofuran

| Solubility1 = 112.332 g/L

| Solvent2 = diethyl ether

| Solubility2= 39.5 g/(100 mL)

| MeltingPtC = 150

| MeltingPt_notes = (decomposes)

}}

| Section3 = {{Chembox Structure

| Coordination =

| SpaceGroup = ''P''2₁/''c''

| Dipole =

}}

| Section4 = {{Chembox Thermochemistry

| DeltaHf = −117 kJ/mol

| DeltaGf = −48.4 kJ/mol

| Entropy = 87.9 J/(mol·K)

| HeatCapacity = 86.4 J/(mol·K)

}}

| Section5 =

| Section6 =

| Section7 = {{Chembox Hazards

| Hazards_ref = <ref>{{CLP Regulation|index=001-002-00-4|page=472}}</ref>

| GHSPictograms = {{GHS02}}{{GHS05}}

| GHSSignalWord = DANGER

| HPhrases = {{H-phrases|260|314}}

| PPhrases = {{P-phrases|223|231+232|280|305+351+338|370+378|422}}<ref name="sigma">{{Sigma-Aldrich|id=199877|name=Lithium aluminium hydride|accessdate=2018-06-1}}</ref>

| ExternalSDS = [https://www.sigmaaldrich.com/MSDS/MSDS/DisplayMSDSPage.do?country=PL&language=EN-generic&productNumber=199877&brand=ALDRICH&PageToGoToURL=https%3A%2F%2Fwww.sigmaaldrich.com%2Fcatalog%2Fproduct%2Faldrich%2F199877%3Flang%3Dpl Lithium aluminium hydride]

| NFPA-S = W

| NFPA_ref = <ref>[https://cameochemicals.noaa.gov/chemical/989 Lithium aluminium hydride]</ref>

| FlashPtC = 125

}}

| Section8 = {{Chembox Related

| OtherFunction_label = [[hydride]]

| OtherFunction = [[aluminium hydride]]<br />[[sodium borohydride]]<br />[[sodium hydride]]<br />[[Sodium aluminium hydride]]

}}

'''Lithium aluminium hydride''', commonly abbreviated to '''LAH''', is an [[inorganic compound]] with the [[chemical formula]] {{chem2|Li[AlH4]|auto=1}} or {{chem2|LiAlH4}}. It is a white solid, discovered by Finholt, Bond and [[Hermann Irving Schlesinger|Schlesinger]] in 1947.<ref name="Schlessinger">{{cite journal|last1=Finholt|first1=A. E.|last2=Bond|first2=A. C.|last3=Schlesinger|first3=H. I.|title=Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry|journal=Journal of the American Chemical Society|year=1947|volume=69|issue=5|pages=1199–1203|doi=10.1021/ja01197a061}}</ref> This compound is used as a [[reducing agent]] in [[organic synthesis]], especially for the reduction of [[ester]]s, [[carboxylic acid]]s, and [[amide]]s. The solid is dangerously reactive toward water, releasing gaseous [[hydrogen]] (H₂). Some related derivatives have been discussed for [[hydrogen storage]].

== Properties, structure, preparation ==

[[File:Lialh4 sem.png|thumb|left|upright|[[scanning electron microscopy|Scanning Electron Microscope]] image of LAH powder]]

LAH is a colourless solid but commercial samples are usually gray due to contamination.<ref name=africa>{{cite encyclopedia |author1=Gerrans, G. C. |author2=Hartmann-Petersen, P. | title = Lithium Aluminium Hydride | encyclopedia = Sasol Encyclopaedia of Science and Technology | publisher = New Africa Books | year = 2007 | page = 143 | isbn = 978-1-86928-384-1 | url = https://books.google.com/books?id=1wS3aWR5SO4C&pg=PA143 }}</ref> This material can be purified by recrystallization from [[diethyl ether]]. Large-scale purifications employ a [[Soxhlet extractor]]. Commonly, the impure gray material is used in synthesis, since the impurities are innocuous and can be easily separated from the organic products. The pure powdered material is [[pyrophoric]], but not its large crystals.<ref>{{cite book |author1=Keese, R. |author2=Brändle, M. |author3=Toube, T. P. | title = Practical Organic Synthesis: A Student's Guide | publisher = John Wiley and Sons | year = 2006 | page = [https://archive.org/details/practicalorganic0000kees/page/134 134] | isbn = 0-470-02966-8 | url = https://archive.org/details/practicalorganic0000kees |url-access=registration }}</ref> Some commercial materials contain [[mineral oil]] to inhibit reactions with atmospheric moisture, but more commonly it is packed in moisture-proof plastic sacks.<ref>{{cite journal | last1 = Andreasen | first1 = A. | last2 = Vegge | first2 = T. | last3 = Pedersen | first3 = A. S. | title = Dehydrogenation Kinetics of as-Received and Ball-Milled LiAlH₄ | journal = Journal of Solid State Chemistry | year = 2005 | volume = 178 | issue = 12 | pages = 3672–3678 | doi = 10.1016/j.jssc.2005.09.027 | url = http://dcwww.camd.dtu.dk/Nabiit/Dehydrogenation%20kinetics%20of%20as-received%20and%20ball-milled%20LiAlH4.pdf | bibcode = 2005JSSCh.178.3672A | access-date = 2010-05-07 | archive-url = https://web.archive.org/web/20160303221434/http://dcwww.camd.dtu.dk/Nabiit/Dehydrogenation%20kinetics%20of%20as-received%20and%20ball-milled%20LiAlH4.pdf | archive-date = 2016-03-03 | url-status = dead }}</ref>

LAH violently reacts with water, including atmospheric moisture, to liberate dihydrogen gas. The reaction proceeds according to the following idealized equation:<ref name="africa" />

:{{chem2|Li[AlH4] + 4 H2O → LiOH + Al(OH)3 + 4 H2}}

This reaction provides a useful method to generate hydrogen in the laboratory. Aged, air-exposed samples often appear white because they have absorbed enough moisture to generate a mixture of the white compounds [[lithium hydroxide]] and [[aluminium hydroxide]].<ref name="sittig">{{cite book | last = Pohanish | first = R. P. | title = Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens | edition = 5th | publisher = William Andrew Publishing | year = 2008 | page = 1540 | isbn = 978-0-8155-1553-1 }}</ref>

=== Structure ===

[[File:Lithium-aluminium-hydride-unit-cell-3D-polyhedra.png|left|upright|thumb|The crystal structure of LAH; Li atoms are purple and {{chem2|AlH4}} tetrahedra are tan.]]

LAH crystallizes in the [[monoclinic]] [[space group]] ''P''2₁/''c''. The [[unit cell]] has the dimensions: ''a'' = 4.82, ''b'' = 7.81, and ''c'' = 7.92 Å, α = γ = 90° and β = 112°. In the structure, {{chem2|Li+}} [[cations]] are surrounded by five {{chem2|[AlH4]−}} [[anions]], which have [[tetrahedral molecular geometry]]. The {{chem2|Li+}} cations are bonded to one [[hydrogen]] atom from each of the surrounding tetrahedral {{chem2|[AlH4]−}} anion creating a [[bipyramid]] arrangement. At high pressures (>2.2 GPa) a phase transition may occur to give β-LAH.<ref name="crystal_structure">{{cite journal |author1=Løvvik, O. M. |author2=Opalka, S. M. |author3=Brinks, H. W. |author4=Hauback, B. C. | title = Crystal Structure and Thermodynamic Stability of the Lithium Alanates LiAlH₄ and Li₃AlH₆ | journal = Physical Review B | year = 2004 | volume = 69 | issue = 13 | pages = 134117 | doi = 10.1103/PhysRevB.69.134117 |bibcode=2004PhRvB..69m4117L }}</ref>

[[File:Lialh4 xrpd.svg|left|thumb|upright|[[X-ray powder diffraction]] pattern of as-received {{chem2|Li[AlH4]}}. The asterisk designates an impurity, possibly [[Lithium chloride|LiCl]].]]

=== Preparation ===

{{chem2|Li[AlH4]}} was first prepared from the reaction between [[lithium hydride]] (LiH) and [[aluminium chloride]]:<ref name="Schlessinger" /><ref name="africa" />

:{{chem2|4 LiH + AlCl3 → Li[AlH4] + 3 LiCl}}

In addition to this method, the industrial synthesis entails the initial preparation of [[sodium aluminium hydride]] from the elements under high pressure and temperature:<ref name="HollemanAF">{{cite book | author = Holleman, A. F., Wiberg, E., Wiberg, N. | title = Lehrbuch der Anorganischen Chemie | edition = 102nd | publisher = de Gruyter | year = 2007 | isbn = 978-3-11-017770-1 | url = https://books.google.com/books?id=mahxPfBdcxcC }}</ref>

:{{chem2|Na + Al + 2 H2 → Na[AlH4]}}

{{chem2|Li[AlH4]}} is then prepared by a [[salt metathesis reaction]] according to:

:{{chem2|Na[AlH4] + LiCl → Li[AlH4] + NaCl}}

which proceeds in a high yield. [[Lithium chloride|LiCl]] is removed by [[filtration]] from an [[diethyl ether|ethereal]] solution of LAH, with subsequent precipitation of LAH to yield a product containing around 1% ''w''/''w'' LiCl.<ref name="HollemanAF" />

An alternative preparation starts from LiH, and metallic Al instead of {{chem2|AlCl3}}. Catalyzed by a small quantity of {{chem2|TiCl3}} (0.2%), the reaction proceeds well using [[dimethylether]] as solvent. This method avoids the cogeneration of salt.<ref>{{cite journal |last1=Xiangfeng |first1=Liu |last2=Langmi |first2=Henrietta W. |last3=McGrady |first3=G. Sean |last4=Craig |first4=M. Jensen |last5=Beattie |first5=Shane D. |last6=Azenwi |first6=Felix F. |title=Ti-Doped LiAlH₄ for Hydrogen Storage: Synthesis, Catalyst Loading and Cycling Performance |journal=J. Am. Chem. Soc. |year=2011 |volume=133 |issue=39 |pages=15593–15597|doi=10.1021/ja204976z|pmid=21863886 }}</ref>

=== Solubility data ===

|+ Solubility of {{chem2|Li[AlH4]}} (mol/L)<ref name=sol>{{cite journal | last1 = Mikheeva | first1 = V. I. | last2 = Troyanovskaya | first2 = E. A. | title = Solubility of Lithium Aluminum Hydride and Lithium Borohydride in Diethyl Ether | journal = Bulletin of the Academy of Sciences of the USSR Division of Chemical Science | year = 1971 | volume = 20 | issue = 12 | pages = 2497–2500 | doi = 10.1007/BF00853610 }}</ref>

|-

!rowspan=2 |Solvent

!colspan=5|Temperature (°C)

! 0 !! 25 !! 50 !! 75 !! 100

![[Diethyl ether]]

| – || 5.92 || – || – || –

![[THF]]

| – || 2.96 || – || – || –

![[Dimethoxyethane|Monoglyme]]

| 1.29 || 1.80 || 2.57 || 3.09 || 3.34

![[Diglyme]]

| 0.26 || 1.29 || 1.54 || 2.06 || 2.06

![[Triethylene glycol dimethyl ether|Triglyme]]

| 0.56 || 0.77 || 1.29 || 1.80 || 2.06

![[Tetraethylene glycol dimethyl ether|Tetraglyme]]

| 0.77 || 1.54 || 2.06 || 2.06 || 1.54

![[Dioxane]]

| – || 0.03 || – || – || –

![[Dibutyl ether]]

| – || 0.56 || – || – || –

LAH is soluble in many [[diethyl ether|ethereal]] solutions. However, it may spontaneously decompose due to the presence of catalytic impurities, though, it appears to be more stable in [[tetrahydrofuran]] (THF). Thus, THF is preferred over, e.g., [[diethyl ether]], despite the lower solubility.<ref name="sol" />

=== Thermal decomposition ===

LAH is [[metastability in molecules|metastable]] at room temperature. During prolonged storage it slowly decomposes to {{chem2|Li3[AlH6]}} (lithium hexahydridoaluminate) and [[Lithium hydride|LiH]].<ref name="Dymova">{{cite journal |author1=Dymova T. N. |author2=Aleksandrov, D. P. |author3=Konoplev, V. N. |author4=Silina, T. A. |author5=Sizareva |author6=A. S. | journal = Russian Journal of Coordination Chemistry | year = 1994 | volume = 20 | pages = 279 }}</ref> This process can be accelerated by the presence of [[catalysis|catalytic]] elements, such as [[titanium]], [[iron]] or [[vanadium]].

[[File:Lialh4 dsc.svg|thumb|[[Differential scanning calorimetry]] of as-received {{chem2|Li[AlH4]}}.]]

When heated LAH decomposes in a three-step [[reaction mechanism]]:<ref name="Dymova" /><ref>{{cite journal | last1 = Dilts | first1 = J. A. | last2 = Ashby | first2 = E. C. | title = Thermal Decomposition of Complex Metal Hydrides | journal = Inorganic Chemistry | year = 1972 | volume = 11 | issue = 6 | pages = 1230–1236 | doi = 10.1021/ic50112a015 }}</ref><ref name="Blanchard">{{cite journal | last1 = Blanchard | first1 = D. | last2 = Brinks | first2 = H. | last3 = Hauback | first3 = B. | last4 = Norby | first4 = P. | title = Desorption of LiAlH₄ with Ti- and V-Based Additives | journal = Materials Science and Engineering B | year = 2004 | volume = 108 | issue = 1–2 | pages = 54–59 | doi = 10.1016/j.mseb.2003.10.114 }}</ref>

{{NumBlk|:|{{chem2|3 Li[AlH4] → Li3[AlH6] + 2 Al + 3 H2}} |{{EquationRef|R1}}}}

{{NumBlk|:|{{chem2|2 Li3[AlH6] → 6 LiH + 2 Al + 3 H2}} |{{EquationRef|R2}}}}

{{NumBlk|:|{{chem2|2 LiH + 2 Al → 2 LiAl + H2}} |{{EquationRef|R3}}}}

{{EquationNote|R1}} is usually initiated by the [[melting]] of LAH in the temperature range 150–170&nbsp;°C,<ref>{{cite journal | last1 = Chen | first1 = J. | last2 = Kuriyama | first2 = N. | last3 = Xu | first3 = Q. | last4 = Takeshita | first4 = H. T. | last5 = Sakai | first5 = T. | title = Reversible Hydrogen Storage via Titanium-Catalyzed LiAlH₄ and Li₃AlH₆ | journal = The Journal of Physical Chemistry B | year = 2001 | volume = 105 | issue = 45 | pages = 11214–11220 | doi = 10.1021/jp012127w }}</ref><ref>{{cite journal | last1 = Balema | first1 = V. | last2 = Pecharsky | first2 = V. K. | last3 = Dennis | first3 = K. W. | title = Solid State Phase Transformations in LiAlH₄ during High-Energy Ball-Milling | journal = Journal of Alloys and Compounds | year = 2000 | volume = 313 | issue = 1–2 | pages = 69–74 | doi = 10.1016/S0925-8388(00)01201-9 | url = https://zenodo.org/record/1260143 }}</ref><ref name="Andreasen">{{cite journal | last1 = Andreasen | first1 = A. | title = Effect of Ti-Doping on the Dehydrogenation Kinetic Parameters of Lithium Aluminum Hydride | journal = Journal of Alloys and Compounds | year = 2006 | volume = 419 | issue = 1–2 | pages = 40–44 | doi = 10.1016/j.jallcom.2005.09.067 }}</ref> immediately followed by decomposition into solid {{chem2|Li3[AlH6]}}, although {{EquationNote|R1}} is known to proceed below the melting point of {{chem2|Li[AlH4]}} as well.<ref>{{cite journal | last1 = Andreasen | first1 = A. | last2 = Pedersen | first2 = A. S. | last3 = Vegge | first3 = T. | title = Dehydrogenation Kinetics of as-Received and Ball-Milled LiAlH₄ | journal = Journal of Solid State Chemistry | year = 2005 | volume = 178 | issue = 12 | pages = 3672–3678 | doi = 10.1016/j.jssc.2005.09.027 | bibcode = 2005JSSCh.178.3672A }}</ref> At about 200&nbsp;°C, {{chem2|Li3[AlH6]}} decomposes into LiH ({{EquationNote|R2}})<ref name="Dymova" /><ref name="Blanchard" /><ref name="Andreasen" /> and Al which subsequently convert into LiAl above 400&nbsp;°C ({{EquationNote|R3}}).<ref name="Blanchard" /> Reaction R1 is effectively irreversible. {{EquationNote|R3}} is reversible with an equilibrium pressure of about 0.25 bar at 500&nbsp;°C. {{EquationNote|R1}} and {{EquationNote|R2}} can occur at room temperature with suitable catalysts.<ref>{{cite journal | last1 = Balema | first1 = V. | first2 = J. W. | last2 = Wiench | first3 = K. W. | last3 = Dennis | first4 = M. | last4 = Pruski | first5 = V. K. | last5 = Pecharsky | title = Titanium Catalyzed Solid-State Transformations in LiAlH₄ During High-Energy Ball-Milling | journal = Journal of Alloys and Compounds | year = 2001 | volume = 329 | issue = 1–2 | pages = 108–114 | doi = 10.1016/S0925-8388(01)01570-5 | url = https://zenodo.org/record/1260145 }}</ref>

=== Thermodynamic data ===

The table summarizes [[thermodynamics|thermodynamic]] data for LAH and reactions involving LAH,<ref name="InorganicHandbook">{{cite book |last=Patnaik |first=P. |url=https://archive.org/details/Handbook_of_Inorganic_Chemistry_Patnaik |title=Handbook of Inorganic Chemicals |publisher=McGraw-Hill |year=2003 |isbn=978-0-07-049439-8 |page=[https://archive.org/details/Handbook_of_Inorganic_Chemistry_Patnaik/page/n530 492]}}</ref><ref>{{cite journal | last1 = Smith | first1 = M. B. | last2 = Bass | first2 = G. E. | title = Heats and Free Energies of Formation of the Alkali Aluminum Hydrides and of Cesium Hydride | journal = Journal of Chemical & Engineering Data | year = 1963 | volume = 8 | issue = 3 | pages = 342–346 | doi = 10.1021/je60018a020 }}</ref> in the form of [[standard state|standard]] [[enthalpy]], [[entropy]], and [[Gibbs free energy]] change, respectively.

{|class="wikitable" style="margin:1em auto; text-align:center"

|+ Thermodynamic data for reactions involving {{chem2|Li[AlH4]}}

! Reaction || ΔH° <br />(kJ/mol) || ΔS° <br />(J/(mol·K)) || ΔG° <br />(kJ/mol) || Comment

| align = left|{{chem2|Li (s) + Al (s) + 2 H2 (g) → Li[AlH4]}} (s) || −116.3 || −240.1 || −44.7 || Standard formation from the elements.

| align = left|LiH (s) + Al (s) + {{frac|3|2}} H₂ (g) → LiAlH₄ (s) || −95.6 || −180.2 || 237.6 || Using ΔH°_f(LiH) = −90.579865, ΔS°_f(LiH) = −679.9, and ΔG°_f(LiH) = −67.31235744.

| align = left|{{chem2|Li[AlH4] (s) → Li[AlH4]}} (l) || 22 || – || – || Heat of fusion. Value might be unreliable.

| align = left|LiAlH₄ (l) → {{1/3}} Li₃AlH₆ (s) + {{2/3}} Al (s) + H₂ (g) || 3.46 || 104.5 || −27.68 || ΔS° calculated from reported values of ΔH° and ΔG°.

== Applications ==

=== Use in organic chemistry ===

Lithium aluminium hydride (LAH) is widely used in organic chemistry as a [[reducing agent]].<ref name="africa" /> It is more powerful than the related [[reagent]] [[sodium borohydride]] owing to the weaker Al-H bond compared to the B-H bond.<ref>{{cite journal | author = Brown, H. C. | title = Reductions by Lithium Aluminum Hydride | journal = Organic Reactions | year = 1951 | volume = 6 | page = 469 | doi = 10.1002/0471264180.or006.10 | isbn = 0-471-26418-0 }}</ref> Often as a solution in [[diethyl ether]] and followed by an acid workup, it will convert [[ester]]s, [[carboxylic acid]]s, [[acyl chloride]]s, [[aldehydes]], and [[ketone]]s into the corresponding [[Alcohol (chemistry)|alcohols]] (see: [[carbonyl reduction]]). Similarly, it converts [[amide]],<ref>{{OrgSynth |author1=Seebach, D.|author2=Kalinowski, H.-O.|author3=Langer, W.|author4=Crass, G.|author5=Wilka, E.-M. | title = Chiral Media for Asymmetric Solvent Inductions. (S,S)-(+)-1,4-bis(Dimethylamino)-2,3-Dimethoxybutane from (R,R)-(+)-Diethyl Tartrate | collvol = 7 | collvolpages = 41 | year = 1991 | prep = cv7p0041 }}</ref><ref>{{OrgSynth |author1=Park, C. H.|author2=Simmons, H. E. | title = Macrocyclic Diimines: 1,10-Diazacyclooctadecane | collvol = 6 | collvolpages = 382 | volume = 54 | pages = 88 | year = 1974 | prep = cv6p0382 }}</ref> [[Nitro compound|nitro]], [[nitrile]], [[imine]], [[oxime]],<ref>{{OrgSynth |author1=Chen, Y. K.|author2=Jeon, S.-J.|author3=Walsh, P. J.|author4=Nugent, W. A. | title = (2S)-(−)-3-exo-(Morpholino)Isoborneol | volume = 82 | pages = 87 | year = 2005 | prep = v82p0087 }}</ref> and [[organic azide]]s into the [[amine]]s (see: [[amide reduction]]). It reduces [[quaternary ammonium cation]]s into the corresponding tertiary amines. Reactivity can be tuned by replacing hydride groups [[reductions with metal alkoxyaluminum hydrides|by alkoxy groups]]. Due to its pyrophoric nature, instability, toxicity, low shelf life and handling problems associated with its reactivity, it has been replaced in the last decade, both at the small-industrial scale and for large-scale reductions by the more convenient related reagent [[Red-Al|sodium bis (2-methoxyethoxy)aluminium hydride]], which exhibits similar reactivity but with higher safety, easier handling and better economics.<ref>{{Cite web | url = https://www.organic-chemistry.org/chemicals/reductions/sodiumbis(2-methoxyethoxy)aluminumhydride-red-al.shtm | title = Red-Al, Sodium bis(2-methoxyethoxy)aluminumhydride | publisher = Organic Chemistry Portal }}</ref>

LAH is most commonly used for the reduction of [[ester]]s<ref>{{OrgSynth |author1=Reetz, M. T.|author2=Drewes, M. W.|author3=Schwickardi, R. | title = Preparation of Enantiomerically Pure α-N,N-Dibenzylamino Aldehydes: S-2-(N,N-Dibenzylamino)-3-Phenylpropanal | collvol = 10 | collvolpages = 256 | volume = 76 | pages = 110 | year = 1999 | prep = v76p0110 }}</ref><ref>{{OrgSynth |author1=Oi, R.|author2=Sharpless, K. B. | title = 3-<nowiki>[</nowiki>(1S)-1,2-Dihydroxyethyl<nowiki>]</nowiki>-1,5-Dihydro-3H-2,4-Benzodioxepine | collvol = 9 | collvolpages = 251 | volume = 73 | pages = 1 | year = 1996 | prep = cv9p0251 }}</ref> and [[carboxylic acid]]s<ref>{{OrgSynth |author1=Koppenhoefer, B.|author2=Schurig, V. | title = (R)-Alkyloxiranes of High Enantiomeric Purity from (S)-2-Chloroalkanoic Acids via (S)-2-Chloro-1-Alkanols: (R)-Methyloxirane | collvol = 8 | collvolpages = 434 | volume = 66 | pages = 160 | year = 1988 | prep = cv8p0434 }}</ref> to primary alcohols; prior to the advent of LAH this was a difficult conversion involving [[sodium]] metal in boiling [[ethanol]] (the [[Bouveault-Blanc reduction]]). [[Aldehyde]]s and [[ketone]]s<ref>{{OrgSynth |author1=Barnier, J. P.|author2=Champion, J.|author3=Conia, J. M. | title = Cyclopropanecarboxaldehyde | collvol = 7 | collvolpages = 129 | volume = 60 | pages = 25 | year = 1981 | prep = cv7p0129 }}</ref> can also be reduced to alcohols by LAH, but this is usually done using milder reagents such as [[sodium borohydride|{{chem2|Na[BH4]}}]]; α, β-unsaturated ketones are reduced to allylic alcohols.<ref>{{OrgSynth |author1=Elphimoff-Felkin, I.|author2=Sarda, P. | title = Reductive Cleavage of Allylic Alcohols, Ethers, or Acetates to Olefins: 3-Methylcyclohexene | collvol = 6 | collvolpages = 769 | volume = 56 | pages = 101 | year = 1977 | prep = cv6p0769 }}</ref> When [[epoxide]]s are reduced using LAH, the reagent attacks the less [[steric effects|hindered]] end of the epoxide, usually producing a secondary or tertiary alcohol. [[Epoxycyclohexane]]s are reduced to give axial alcohols preferentially.<ref>{{cite journal | last1 = Rickborn | first1 = B. | last2 = Quartucci | first2 = J. | title = Stereochemistry and Mechanism of Lithium Aluminum Hydride and Mixed Hydride Reduction of 4-''t''-Butylcyclohexene Oxide | journal = The Journal of Organic Chemistry | year = 1964 | volume = 29 | issue = 11 | pages = 3185–3188 | doi = 10.1021/jo01034a015 }}</ref>

Partial reduction of [[acid chloride]]s to give the corresponding aldehyde product cannot proceed via LAH, since the latter reduces all the way to the primary alcohol. Instead, the milder [[Lithium tri-tert-butoxyaluminum hydride|lithium tri-''tert''-butoxyaluminum hydride]], which reacts significantly faster with the acid chloride than with the aldehyde, must be used. For example, when [[isovaleric acid]] is treated with [[thionyl chloride]] to give isovaleroyl chloride, it can then be reduced via lithium tri-''tert''-butoxyaluminum hydride to give isovaleraldehyde in 65% yield.<ref>{{cite book | author = Wade, L. G. Jr. | title = Organic Chemistry | edition = 6th | publisher = Pearson Prentice Hall | year = 2006 | isbn = 0-13-147871-0 }}</ref><ref>{{cite book |last1=Wade |first1=L. G. |title=Organic chemistry |date=2013 |publisher=Pearson |location=Boston |isbn=978-0-321-81139-4 |pages=835 |edition=8th}}</ref>

File:LAH rxns.png|

rect 5 12 91 74 [[Alcohol (chemistry)|alcohol]]

rect 121 9 193 69 [[Alcohol (chemistry)|alcohol2]]

rect 337 1 414 60 [[Alcohol (chemistry)|alcohol3]]

rect 458 55 526 117 [[Alcohol (chemistry)|alcohol4]]

rect 128 311 204 366 [[amine]]1

rect 457 362 529 413 [[Alcohol (chemistry)|alcohol5]]

rect 381 255 433 273 [[Azide#Organic azides|azide]]

rect 469 244 525 269 [[amine]]2

#[https://web.archive.org/web/20080327003154/http://tools.wikimedia.de/~dapete/ImageMapEdit/ImageMapEdit.html?en This image editor] was used.

Lithium aluminium hydride also reduces [[alkyl halide]]s to [[alkane]]s.<ref>{{cite journal | last1 = Johnson | first1 = J. E. | last2 = Blizzard | first2 = R. H. | last3 = Carhart | first3 = H. W. | title = Hydrogenolysis of Alkyl Halides by Lithium Aluminum Hydride | journal = Journal of the American Chemical Society | year = 1948 | volume = 70 | issue = 11 | pages = 3664–3665 | pmid = 18121883 | doi = 10.1021/ja01191a035 }}</ref><ref>{{cite journal | last1 = Krishnamurthy | first1 = S. | last2 = Brown | first2 = H. C. | title = Selective Reductions. 28. The Fast Reaction of Lithium Aluminum Hydride with Alkyl Halides in THF. A Reappraisal of the Scope of the Reaction | journal = The Journal of Organic Chemistry | year = 1982 | volume = 47 | issue = 2 | pages = 276–280 | doi = 10.1021/jo00341a018 }}</ref> Alkyl iodides react the fastest, followed by alkyl bromides and then alkyl chlorides. Primary halides are the most reactive followed by secondary halides. Tertiary halides react only in certain cases.<ref>{{cite book | author = Carruthers, W. | title = Some Modern Methods of Organic Synthesis | publisher = Cambridge University Press | year = 2004 | page = 470 | isbn = 0-521-31117-9 | url = https://books.google.com/books?id=ti7yMYYW7CMC&pg=PA470 }}</ref>

Lithium aluminium hydride does not reduce simple [[alkene]]s or [[arene]]s. [[Alkyne]]s are reduced only if an alcohol group is nearby.<ref>{{OrgSynth |author1=Wender, P. A.|author2=Holt, D. A.|author3=Sieburth, S. Mc N.|author3-link=Scott Sieburth | title = 2-Alkenyl Carbinols from 2-Halo Ketones: 2-E-Propenylcyclohexanol | collvol = 7 | collvolpages = 456 | volume = 64 | pages = 10 | year = 1986 | prep = cv7p0456 }}</ref> It was observed that the {{chem2|LiAlH4}} reduces the double bond in the ''N''-allylamides.<ref>{{Cite journal|title=Reduction of N-allylamides by LiAlH₄: Unexpected Attack of the Double Bond With Mechanistic Studies of Product and Byproduct Formation|year = 2014|pmid = 25347383|last1 = Thiedemann|first1 = B.|last2 = Schmitz|first2 = C. M.|last3 = Staubitz|first3 = A.|journal = The Journal of Organic Chemistry|volume = 79|issue = 21|pages = 10284–95|doi = 10.1021/jo501907v}}</ref>

=== Inorganic chemistry ===

LAH is widely used to prepare main group and transition [[metal hydrides]] from the corresponding metal [[halide]]s.

:

:LiAlH₄ + 4NH₃ → Li[Al(NH₂)₄] + 4H₂

=== Hydrogen storage ===

LiAlH₄ contains 10.6 wt% hydrogen, thereby making LAH a potential [[hydrogen storage]] medium for future [[fuel cell]]-powered [[vehicle]]s. The high hydrogen content, as well as the discovery of reversible hydrogen storage in Ti-doped NaAlH₄,<ref>{{cite journal | last1 = Bogdanovic | first1 = B. | last2 = Schwickardi | first2 = M. | title = Ti-Doped Alkali Metal Aluminium Hydrides as Potential Novel Reversible Hydrogen Storage Materials | journal = Journal of Alloys and Compounds | year = 1997 | volume = 253–254 | pages = 1–9 | doi = 10.1016/S0925-8388(96)03049-6 }}</ref> have sparked renewed research into LiAlH₄ during the last decade. A substantial research effort has been devoted to accelerating the decomposition kinetics by catalytic doping and by [[ball mill]]ing.<ref name="varin">{{cite book | last1 = Varin | first1 = R. A. |author-link1=Robert A. Varin| last2 = Czujko | first2 = T. | last3 = Wronski | first3 = Z. S. | title = Nanomaterials for Solid State Hydrogen Storage | edition = 5th | year = 2009 | pages = 338 | publisher = Springer | isbn = 978-0-387-77711-5 }}</ref>

In order to take advantage of the total hydrogen capacity, the intermediate compound [[LiH]] must be dehydrogenated as well. Due to its high thermodynamic stability this requires temperatures in excess of 400&nbsp;°C, which is not considered feasible for transportation purposes. Accepting LiH + Al as the final product, the hydrogen storage capacity is reduced to 7.96 wt%. Another problem related to hydrogen storage is the recycling back to LiAlH₄ which, owing to its relatively low stability, requires an extremely high hydrogen pressure in excess of 10000 bar.<ref name="varin" /> Cycling only reaction R2 — that is, using Li₃AlH₆ as starting material — would store 5.6 wt% hydrogen in a single step (vs. two steps for NaAlH₄ which stores about the same amount of hydrogen). However, attempts at this process have not been successful so far.{{citation needed|date=March 2016}}

=== Other tetrahydridoaluminiumates ===

A variety of salts analogous to LAH are known. [[Sodium hydride|NaH]] can be used to efficiently produce [[sodium aluminium hydride]] (NaAlH₄) by [[Salt metathesis reaction|metathesis]] in THF:

[[Potassium aluminium hydride]] (KAlH₄) can be produced similarly in [[diglyme]] as a solvent:<ref name=react>{{cite journal | last1 = Santhanam | first1 = R. | last2 = McGrady | first2 = G. S. | title = Synthesis of Alkali Metal Hexahydroaluminate Complexes Using Dimethyl Ether as a Reaction Medium | journal = Inorganica Chimica Acta | year = 2008 | volume = 361 | issue = 2 | pages = 473–478 | doi = 10.1016/j.ica.2007.04.044 }}</ref>

The reverse, i.e., production of LAH from either sodium aluminium hydride or potassium aluminium hydride can be achieved by reaction with [[lithium chloride|LiCl]] or lithium hydride in [[diethyl ether]] or [[THF]]:<ref name="react" />

"Magnesium alanate" (Mg(AlH₄)₂) arises similarly using [[magnesium bromide|MgBr₂]]:<ref>{{cite book |author1=Wiberg, E. |author2=Wiberg, N. |author3=Holleman, A. F. | title = Inorganic Chemistry | year = 2001 | page = 1056 | publisher = Academic Press | isbn = 0-12-352651-5 | url = https://books.google.com/books?id=vEwj1WZKThEC&pg=PA1056 }}</ref>

[[Red-Al]] (or SMEAH, NaAlH₂(OC₂H₄OCH₃)₂) is synthesized by reacting sodium aluminum tetrahydride (NaAlH₄) and [[2-methoxyethanol]]:<ref>{{cite journal |author1=Casensky, B. |title=The chemistry of sodium alkoxyaluminium hydrides. I. Synthesis of sodium bis(2-methoxyethoxy)aluminium hydride |author2=Machacek, J. |author3=Abraham, K. | journal = Collection of Czechoslovak Chemical Communications | year = 1971 | volume = 36 |issue=7 | pages = 2648–2657 |doi=10.1135/cccc19712648 }}</ref>

== See also ==

{{Commons category|Lithium aluminium hydride|lcfirst=yes}}

== References ==

{{Reflist}}

== Further reading ==

*{{cite book |author1=Wiberg, E. |author2=Amberger, E. | title = Hydrides of the Elements of Main Groups I-IV | publisher = Elsevier | year = 1971 | isbn = 0-444-40807-X }}

*{{cite book | author = Hajos, A. | title = Complex Hydrides and Related Reducing Agents in Organic Synthesis | publisher = Elsevier | year = 1979 | isbn = 0-444-99791-1 }}

*{{cite book | editor = Lide, D. R. | title = Handbook of Chemistry and Physics | publisher = CRC Press | year = 1997 | isbn = 0-8493-0478-4 }}

*{{cite book | author = Carey, F. A. | title = Organic Chemistry with Online Learning Center and Learning by Model CD-ROM | publisher = McGraw-Hill | year = 2002 | isbn = 0-07-252170-8 | url = http://www.chem.ucalgary.ca/courses/351/Carey5th/Carey.html }}

*{{cite book | author = Andreasen, A. | title = Hydrogen Storage Materials with Focus on Main Group I-II Elements | chapter = Chapter 5: Complex Hydrides | publisher = Risø National Laboratory | year = 2005 | isbn = 87-550-3498-5 | chapter-url = http://www.risoe.dk/rispubl/AFM/afmpdf/ris-phd-21.pdf | url-status = dead | archive-url = https://web.archive.org/web/20120819163021/http://www.risoe.dk/rispubl/AFM/afmpdf/ris-phd-21.pdf | archive-date = 2012-08-19 }}

== External links ==

*{{cite web | title = Usage of LiAlH₄ | url = http://www.orgsyn.org/orgsyn/chemname.asp?nameID=36257 | publisher = Organic Syntheses }}

*{{cite web | url = https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=28112 | publisher = PubChem | title = Lithium Tetrahydridoaluminate – Compound Summary (CID 28112) }}

*{{cite web | url = http://webbook.nist.gov/cgi/cbook.cgi?Formula=LiAlH4&NoIon=on&Units=SI | title = Lithium Tetrahydridoaluminate | publisher = NIST | work = WebBook }}

*{{cite web|url=http://msds.ehs.cornell.edu/msds/MSDSDOD/A441/M220131.htm |title=Materials Safety Data Sheet |publisher=Cornell University |url-status=dead |archive-url=https://web.archive.org/web/20060308045012/http://msds.ehs.cornell.edu/msds/MSDSDOD/A441/M220131.htm |archive-date=March 8, 2006 }}

*{{cite web|url=http://hydpark.ca.sandia.gov/ |publisher=Sandia National Laboratory |title=Hydride Information Center |url-status=dead |archive-url=https://web.archive.org/web/20050507175350/http://hydpark.ca.sandia.gov/ |archive-date=May 7, 2005 }}

*{{cite web|url=http://www.chem2.bham.ac.uk/labs/cox/Teaching/4th_Year/II/Reduction_Reactions.pdf |archive-url=http://arquivo.pt/wayback/20160523233903/http://www.chem2.bham.ac.uk/labs/cox/Teaching/4th_Year/II/Reduction_Reactions.pdf |url-status=dead |archive-date=May 23, 2016 |title=Reduction Reactions |publisher=University of Birmingham |work=Teaching Resources – 4th Year }}

{{aluminium compounds}}

[[Category:Aluminium complexes]]

[[Category:Substances discovered in the 1940s]]