View source for Aluminium hydride

{{Use British English|date=July 2022}}<!--...but not for spellings in citations-->
{{Chembox
|Watchedfields = changed
|verifiedrevid = 477001731
|ImageFile = Aluminium-hydride-unit-cell-3D-vdW.png
|ImageName = Unit cell spacefill model of aluminium hydride
|PIN = Aluminium hydride
|SystematicName = Alumane
|OtherNames = {{ubl|Alane|Aluminic hydride|Aluminium(III) hydride|Aluminium trihydride|Trihydridoaluminium}}
|Section1={{Chembox Identifiers
|InChI1 = 1/Al.3H/rAlH3/h1H3
|InChIKey1 = AZDRQVAHHNSJOQ-FSBNLZEDAV
|CASNo = 7784-21-6
|CASNo_Ref = {{cascite|correct|CAS}}
|UNII_Ref = {{fdacite|correct|FDA}}
|UNII = KZJ3T010RQ
|PubChem = 14488
|PubChem1 = 14399066
|PubChem1_Comment = (<sup>2</sup>''H''<sub>3</sub>)
|PubChem2 = 16721258
|PubChem2_Comment = (<sup>3</sup>''H''<sub>3</sub>)
|ChemSpiderID = 13833
|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID1_Ref = {{chemspidercite|correct|chemspider}}
|ChemSpiderID1 = 17625618
|ChemSpiderID1_Comment = (<sup>3</sup>''H''<sub>3</sub>)
|ChEBI_Ref = {{ebicite|correct|EBI}}
|ChEBI = 30136
|StdInChI_Ref = {{stdinchicite|correct|chemspider}}
|StdInChI = 1S/Al.3H
|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
|StdInChIKey = AZDRQVAHHNSJOQ-UHFFFAOYSA-N
|SMILES = [AlH3]
|InChI = 1S/Al.3H
|InChIKey = AZDRQVAHHNSJOQ-UHFFFAOYSA-N
|Gmelin = 245
}}
|Section2={{Chembox Properties
|Al=1|H=3
|Appearance = white crystalline solid, non-volatile, highly polymerized, needle-like crystals
|Density = 1.477 g/cm<sup>3</sup>, solid
|MeltingPtC = 150
|MeltingPt_notes = starts decomposing at {{convert|105|C}}
|Solubility = reacts
|SolubleOther = soluble in [[diethyl ether|ether]] <br> reacts in [[ethanol]]
}}
|Section4={{Chembox Thermochemistry
|DeltaHf = −11.4 kJ/mol
|DeltaGf = 46.4 kJ/mol
|Entropy = 30 J/(mol·K)
|HeatCapacity = 40.2 J/(mol·K)
}}
|Section8={{Chembox Related
|OtherCompounds = [[Lithium aluminium hydride]], [[diborane]]
}}
}}
'''Aluminium hydride''' (also known as '''alane''' and '''alumane''') is an [[inorganic compound]] with the [[Chemical formula|formula]] {{chem2|AlH3|auto=1}}. Alane and its derivatives are part of a family of common [[Redox|reducing]] reagents in [[organic synthesis]] based around [[group 13 hydride]]s.<ref>{{cite journal |author1=Brown, H. C. |author2=Krishnamurthy, S. | title = Forty Years of Hydride Reductions | journal = [[Tetrahedron (journal)|Tetrahedron]] | year = 1979 | volume = 35 | issue = 5 | pages = 567–607 | doi = 10.1016/0040-4020(79)87003-9}}</ref> In solution—typically in ethereal solvents such [[tetrahydrofuran]] or [[diethyl ether]]—aluminium hydride forms complexes with [[Lewis base]]s, and reacts selectively with particular organic [[functional group]]s (e.g., with [[carboxylic acid]]s and [[ester]]s over [[organic halide]]s and [[nitro group]]s), and although it is not a reagent of choice, it can react with carbon-carbon multiple bonds (i.e., through [[Alkenylaluminium compounds|hydroalumination]]). Given its density, and with hydrogen content on the order of 10% by weight,<ref name = h2storage/> some forms of alane are, as of 2016,<ref>{{cite journal |url=https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.201600338 |title=Towards Direct Synthesis of Alane: A Predicted Defect-Mediated Pathway Confirmed Experimentally |journal=ChemSusChem |year=2016 |doi=10.1002/cssc.201600338 |author1=Lin-Lin Wang |author2=Aditi Herwadkar |author3=Jason M. Reich |author4= Duane D. Johnson |author5= Stephen D. House |author6=Pamela Peña-Martin |author7=Angus A. Rockett |author8= Ian M. Robertson |author9= Shalabh Gupta |author10= Vitalij K. Pecharsky |volume=9 |issue=17 |pages=2358–2364|pmid=27535100|bibcode=2016ChSCh...9.2358W }}</ref> active candidates for storing hydrogen and so for power generation in fuel cell applications, including electric vehicles.{{citation needed lead|date = July 2022}} As of 2006 it was noted that further research was required to identify an efficient, economical way to reverse the process, regenerating alane from spent aluminium product.

Solid aluminium hydride, or alane, is colorless and nonvolatile, and in its most common reagent form it is a highly [[polymer]]ized species (i.e., has multiple {{chem2|AlH3}} units that are self-associated); it melts with decomposition at 110 °C.<ref name = EROSv08/> While not spontaneously flammable, alane solids and solutions require precautions in use akin to other highly flammable [[metal hydride]]s, and must be handled and stored with the active exclusion of moisture. Alane decomposes on exposure to air (principally because of adventitious moisture), though [[Passivation (chemistry) | passivation]] — here, allowing for development of an inert surface coating — greatly diminishes the rate of decomposition of alane preparations.{{citation needed lead|date = July 2022}}

==Form and structure==
{{refimprove section |date=July 2022}}
Alane is a colorless and nonvolatile solid that melts with decomposition at 110 °C;<ref name = EROSv08/> sufficiently large samples may be further heated to complete decomposition at 150&nbsp;°C.<ref name=HS5p401>{{ cite book | title = Inorganic Chemistry | last1 = Housecroft | first1 = C. E. | last2 = Sharpe | first2 = A. G. | year = 2018 | publisher = [[Prentice-Hall]] | edition = 5th | isbn = 978-0273742753 | page = 401 }}</ref>  The solid form, however, often presents as a white solid that may be tinted grey (with decreasing reagent particle size or increasing impurity levels).{{cn|date = July 2022}} This coloration arises from a thin surface [[passivation (chemistry)|passivation]] layer of aluminium oxide or hydroxide.{{cn|date = July 2022}}

Under common laboratory conditions, alane is "highly polymeric", structurally.<ref name = EROSv08 /> This is sometimes indicated with the formula {{chem2|(AlH3)_{''n''}|}}, where ''n'' is left unspecified.<ref>See, e.g., {{harvnb|Andrews|Wang|2003}}.</ref>{{primary src inline|date=February 2024}} Preparations of alane dissolve in [[tetrahydrofuran]] (THF) or [[diethyl ether]] (ether),<ref name = EROSv08/> from which pure allotropes precipitate.<ref name = lund>{{cite patent | inventor = Lund, G. K.; Hanks, J. M.; Johnston, H. E. | country = US | status = application | number = 2007066839 | title = Method for the Production of α-Alane.}}</ref>{{primary source inline|date = July 2022}}

Structurally, alane can adopt numerous [[Polymorphism (materials science)|polymorphic forms]]. By 2006, "at least 7 non-solvated {{chem2|AlH3}} phases" were known: α-, α’-, β-, γ-, ε-, and ζ-alanes;<ref name = h2storage/> the δ- and θ-alanes have subsequently been discovered.{{cn|date=July 2022}} Each has a different structure, with α-alane being the most thermally stable polymorph.{{cn|date=July 2022}} For instance, [[crystallography|crystallographically]], α-alane adopts a cubic or rhombohedral morphology, while α’-alane forms needle-like crystals and γ-alane forms bundles of fused needles.{{cn|date=July 2022}} The crystal structure of α-alane has been determined, and features aluminium atoms surrounded by six octahedrally oriented hydrogen atoms that bridge to six other aluminium atoms (see table), where the Al-H distances are all equivalent (172 pm) and the Al-H-Al angle is 141°.<ref>{{harvnb|Turley|Rinn|1969}}. (Abstract) "The final Al⋯H distance of 1.72&nbsp;Å, the participation of each Al in six bridges, and the equivalence of all Al⋯H distances suggest that 3c-2e bonding occurs." Angle is lasted as "Al(6)-H(5)-Al(4)" in Table IV.</ref>

{| class="wikitable" width="auto" style="text-align: center"
|-
! colspan="6" |Crystallographic Structure of α-{{chem2|AlH3}}<ref name = Crystal/>
|- style="background:#efefef;"
! The α-{{chem2|AlH3}} [[unit cell]]
! Aluminium coordination
! Hydrogen coordination
|-
| style="text-align:left;" |[[File:Aluminium-hydride-unit-cell-3D-balls.png|150px]]
| style="text-align:left;" |[[File:Aluminium-hydride-Al-coordination-3D-balls.png|125px]]
| style="text-align:center;" |[[File:Aluminium-hydride-H-coordination-3D-balls.png|150px]]
|}

When β- and γ-alanes are produced together, they convert to α-alane upon heating, while δ-, ε-, and θ-alanes are produced in still other crystallization conditions; although they are less thermally stable, the δ-, ε-, and θ-alane polymorphs do not convert to α-alane upon heating.<ref name = lund/>{{better source|date = July 2022}}

Under special conditions, non-polymeric alanes (i.e., molecular forms of it) can be prepared and studied. Monomeric {{chem2|AlH3}} has been isolated at low temperature in a solid [[noble gas]] matrix where it was shown to be planar.<ref>{{cite journal | title = Molecular Aluminium Trihydride, AlH<sub>3</sub>: Generation in a Solid Noble Gas Matrix and Characterisation by its Infrared Spectrum and ''ab initio'' Calculations |author1=Kurth, F. A. |author2=Eberlein, R. A. |author3=Schnöckel, H.-G. |author4=Downs, A. J. |author5=Pulham, C. R. | journal = Journal of the Chemical Society, Chemical Communications | year = 1993 | volume = 1993 | issue = 16 | pages = 1302–1304 | doi = 10.1039/C39930001302}} (Abstract) Broad-band photolysis of a solid noble gas matrix containing Al atoms and H<sub>2</sub> gives rise to the planar, monomeric AlH<sub>3</sub> molecule.</ref> The dimeric form, {{chem2|Al2H6}}, has been isolated in solid hydrogen, and it is [[isostructural]] with [[diborane]] ({{chem2|B2H6}}) and [[digallane]] ({{chem2|Ga2H6}}).<ref>{{cite journal | title = The Infrared Spectrum of Al<sub>2</sub>H<sub>6</sub> in Solid Hydrogen |last1=Andrews |first1=Lester |author2=Wang Xuefeng | journal = Science | year = 2003 | volume = 299 | issue = 5615 | pages = 2049–2052 | doi = 10.1126/science.1082456 | pmid = 12663923 |bibcode = 2003Sci...299.2049A |s2cid=45856199 |jstor=3833717 |ref={{harvid|Andrews|Wang|2003}}}} See also emendations at {{doi|10.1126/science.300.5620.741a}}.</ref><ref name = "Pulham">{{cite journal | title = Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga<sub>2</sub>H<sub>6</sub> as Determined by Electron Diffraction |author1=Pulham, C. R. |author2=Downs, A. J. |author3=Goode, M. J. |author4=Rankin D. W. H. |author5=Robertson, H. E. | journal = Journal of the American Chemical Society | year = 1991 | volume = 113 | issue = 14 | pages = 5149–5162 | doi = 10.1021/ja00014a003}}</ref><ref>{{Cite book |last=Housecroft |first=Catherine |title=Inorganic Chemistry |date=2018 |isbn=978-1-292-13414-7 |edition=5th |pages=397|publisher=Pearson }}</ref>

==Handling==
Alane is not spontaneously flammable.<ref>{{harvnb|Galatsis|Sintim|Wang|2008}}, which describes the phenomenon using [[Combustibility_and_flammability#Definitions|the synonym "inflammable"]].</ref> Even so, "similar handling and precautions as... exercised for {{chem2|Li[AlH4]}}" (the chemical reagent, [[lithium aluminium hydride]]) are recommended, as its "reactivity [is] comparable" to this related reducing reagent.<ref name = EROSv08/> For these reagents, both preparations in solutions and isolated solids are "highly flammable and must be stored in the absence of moisture".<ref name = EROSv04 /> Laboratory guides recommend alane use inside a [[fume hood]].<ref name = EROSv08/>{{why|date = July 2022}}<!--Presumably b/c of fire risk+combustion products are corrosive, but need a cite.--> Solids of this reagent type carry recommendations of handling "in a glove bag or [[glove box|dry box]]".<ref name = EROSv04/> After use, solution containers are typically sealed tightly with concomitant flushing with inert gas to exclude the oxygen and moisture of ambient air.<ref name = EROSv04/>

[[Passivation (chemistry)|Passivation]]{{what|date = July 2022}} greatly diminishes the decomposition rate associated with alane preparations.{{cn|date = July 2022}} Passivated alane nevertheless retains a hazard classification of 4.3 (chemicals which in contact with water, emit flammable gases).<ref>2013 CFR Title 29 Volume 6 Section 1900.1200 Appendix B.12</ref>

=== Reported accidents ===
{{expand section | with = a careful, source-derived presentation of accidents known to be associated with use of this agent, at small and large scale |small = no | date = July 2022}}
Alane reductions are believed to proceed via an intermediate [[coordination complex]], with aluminum attached to the partially reduced functional group, and liberated when the reaction undergoes protic [[quenching (chemistry)|quenching]]. If the substrate is also [[fluoroalkane|fluorinated]], the intermediate may instead explode if exposed to a [[hot spot (fire safety)|hot spot]] above 60°C.<ref>{{cite journal | last=Taydakov | first=Ilya V. | title=Serious Explosion during Large-Scale Preparation of an Amine by Alane (AlH3) Reduction of a Nitrile Bearing a CF<sub>3</sub> Group | journal=ACS Chemical Health & Safety | publisher=American Chemical Society (ACS) | volume=27 | issue=4 | date=2020-07-08 | issn=1871-5532 | doi=10.1021/acs.chas.0c00045 | pages=235–239| s2cid=225542103}}</ref>

==Preparation==
Aluminium hydrides and various complexes thereof have long been known.<ref>{{cite journal |author1=Brower, F. M. |author2=Matzek, N. E. |author3=Reigler, P. F. |author4=Rinn, H. W. |author5=Schmidt, D. L. |author6=Snover, J. A. |author7=Terada, K. | title = Preparation and Properties of Aluminum Hydride | journal = [[Journal of the American Chemical Society]] | year = 1976 | volume = 98 | issue = 9 | pages = 2450–2454 | doi = 10.1021/ja00425a011}}</ref> Its first synthesis was published in 1947, and a patent for the synthesis was assigned in 1999.<ref>{{cite journal |author1=Finholt, A. E. |author2=Bond, A. C. Jr. |author3=Schlesinger, 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><ref>{{cite patent | country = US | number = 6228338 | status = patent | title = Preparation of Aluminum Hydride Polymorphs, Particularly Stabilized α-AlH<sub>3</sub> | inventor = Petrie, M. A.; Bottaro, J. C.; Schmitt, R. J.; Penwell, P. E.; Bomberger, D. C. | gdate = 2001-05-08}}</ref> Aluminium hydride is prepared by treating [[lithium aluminium hydride]] with [[aluminium trichloride]].<ref>{{cite book |author1=Schmidt, D. L. |author2=Roberts, C. B. |author3=Reigler, P. F. |author4=Lemanski, M. F. Jr. |author5=Schram, E. P. |chapter=Aluminum Trihydride-diethyl etherate ( ''Etherated Alane'' ) | title = Inorganic Syntheses | year = 1973 | volume = 14 | pages = 47–52 | doi = 10.1002/9780470132456.ch10 | isbn = 9780470132456}}</ref> The procedure is intricate: attention must be given to the removal of [[lithium chloride]].
:{{chem2|3 Li[AlH4] + AlCl3 → 4 AlH3 + 3 LiCl}}

The ether solution of alane requires immediate use, because polymeric material rapidly precipitates as a solid. Aluminium hydride solutions are known to degrade after 3 days. Aluminium hydride is more reactive than {{chem2|Li[AlH4]}}.<ref name = lund/>

Several other methods exist for the preparation of aluminium hydride:
:{{chem2|2 Li[AlH4] + BeCl2 → 2 AlH3 + Li2[BeH2Cl2]}}
:{{chem2|2 Li[AlH4] + H2SO4 → 2 AlH3 + Li2SO4 + 2 H2}}
:{{chem2|2 Li[AlH4] + ZnCl2 → 2 AlH3 + 2 LiCl + ZnH2}}
:{{chem2|2 Li[AlH4] + I2 → 2 AlH3 + 2 LiI + H2}}

===Electrochemical synthesis===
Several groups have shown that alane can be produced [[Electrochemistry|electrochemically]].<ref>{{cite journal |author1=Alpatova, N. M. |author2=Dymova, T. N. |author3=Kessler, Yu. M. |author4=Osipov, O. R. | title = Physicochemical Properties and Structure of Complex Compounds of Aluminium Hydride | journal = Russian Chemical Reviews | year = 1968 | volume = 37 | issue = 2 | pages = 99–114 | doi = 10.1070/RC1968v037n02ABEH001617 |bibcode = 1968RuCRv..37...99A|s2cid=250839118}}</ref><ref>{{cite journal |author1=Semenenko, K. N. |author2=Bulychev, B. M. |author3=Shevlyagina, E. A. | title = Aluminium Hydride | journal = Russian Chemical Reviews | year = 1966 | volume = 35 | issue = 9 | pages = 649–658 | doi = 10.1070/RC1966v035n09ABEH001513 |bibcode = 1966RuCRv..35..649S |s2cid=250889877}}</ref><ref>{{cite journal |title=none|author1=Osipov, O. R. |author2=Alpatova, N. M. |author3=Kessler, Yu. M. | journal = Elektrokhimiya | volume = 2 | page = 984 | year = 1966}}</ref><ref name="ReferenceA">{{cite journal |author1=Zidan, R. |author2=Garcia-Diaz, B. L. |author3=Fewox, C. S. |author4=Stowe, A. C. |author5=Gray, J. R. |author6=Harter, A. G. |s2cid=21479330 | title = Aluminium hydride: a reversible material for hydrogen storage | journal = Chemical Communications | year = 2009 | issue = 25 | pages = 3717–3719 | doi = 10.1039/B901878F |pmid=19557259 |url=https://zenodo.org/record/1229996}}</ref><ref name="ReferenceB">{{cite journal |author1=Martinez-Rodriguez, M. J. |author2=Garcia-Diaz, B. L. |author3=Teprovich, J. A. |author4=Knight, D. A. |author5=Zidan, R. | title = Advances in the electrochemical regeneration of aluminum hydride | journal = Applied Physics A: Materials Science & Processing | year = 2012 | volume = 106 | issue = 25 | pages = 545–550 | doi = 10.1007/s00339-011-6647-y |bibcode = 2012ApPhA.106..545M |s2cid=93879202}}</ref> Different electrochemical alane production methods have been patented.<ref>{{cite patent | country = DE | inventor = Clasen, H. | status = patent | number = 1141623 | title = Verfahren zur Herstellung von Aluminiumhydrid bzw. aluminiumwasserstoffreicher komplexer Hydride | gdate = 1962-12-27 | assign1 = Metallgesellschaft}}</ref><ref>{{cite patent | country = US | inventor = Zidan, R. | status = patent | number = 8470156 | title = Electrochemical process and production of novel complex hydrides | gdate = 2013-06-25 | assign1 = Savannah River Nuclear Solutions, LLC}}</ref> Electrochemically generating alane avoids chloride impurities. Two possible mechanisms are discussed for the formation of alane in Clasen's electrochemical cell containing [[Tetrahydrofuran|THF]] as the solvent, [[sodium aluminium hydride]] as the electrolyte, an aluminium anode, and an iron (Fe) wire submerged in [[Mercury (element)|mercury]] (Hg) as the cathode. The sodium forms an [[Amalgam (chemistry)|amalgam]] with the Hg cathode preventing side reactions and the hydrogen produced in the first reaction could be captured and reacted back with the sodium mercury amalgam to produce sodium hydride. Clasen's system results in no loss of starting material. For insoluble anodes, reaction 1 occurs, while for soluble anodes, anodic dissolution is expected according to reaction 2:

# {{chem2|[AlH4]−}} − {{chem2|[[Electron|e−]] + ''n'' THF → AlH3*''n''THF + 1/2 H2}}
# {{chem2|3 [AlH4]− + Al}} − {{chem2|3 e− + 4''n'' THF → 4 AlH3*''n''THF}}

In reaction 2, the aluminium anode is consumed, limiting the production of aluminium hydride for a given electrochemical cell.

The crystallization and recovery of aluminium hydride from electrochemically generated alane has been demonstrated.<ref name="ReferenceA"/><ref name="ReferenceB"/>

===High pressure hydrogenation of aluminium===
α-{{chem2|AlH3}} can be produced by hydrogenation of aluminium at 10 [[GPa]] and {{convert|600|C}}. The reaction between the liquified hydrogen produces α-{{chem2|AlH3}} which could be recovered under ambient conditions.<ref name="SaitohSakurai2010">{{cite journal|last1=Saitoh|first1=H|last2=Sakurai|first2=Y|last3=Machida|first3=A|last4=Katayama|first4=Y|last5=Aoki|first5=K|title=In situX-ray diffraction measurement of the hydrogenation and dehydrogenation of aluminum and characterization of the recovered AlH3|journal=Journal of Physics: Conference Series|volume=215|issue=1|year=2010|pages=012127|issn=1742-6596|doi=10.1088/1742-6596/215/1/012127|bibcode = 2010JPhCS.215a2127S |doi-access=free}}</ref>

==Reactions==
===Formation of adducts with Lewis bases===
{{chem2|AlH3}} readily forms adducts with strong [[Lewis acids and bases|Lewis bases]]. For example, both 1:1 and 1:2 complexes form with [[trimethylamine]]. The 1:1 complex is tetrahedral in the gas phase,<ref name = "greenwood">{{Greenwood&Earnshaw}}</ref> but in the solid phase it is dimeric with bridging hydrogen centres, {{chem2|(N(CH3)3Al(μ\-H))2}}.<ref>{{cite journal | title = Tertiary Amine Stabilized Dialane |author1=Atwood, J. L. |author2=Bennett, F. R. |author3=Elms, F. M. |author4=Jones, C. |author5=Raston, C. L. |author-link5=Colin L. Raston |author6=Robinson, K. D. | journal = Journal of the American Chemical Society | year = 1991 | volume = 113 | issue = 21 | pages = 8183–8185 | doi = 10.1021/ja00021a063}}</ref> The 1:2 complex adopts a [[Trigonal bipyramid molecular geometry|trigonal bipyramidal structure]].<ref name = "greenwood"/> Some adducts (e.g. dimethylethylamine alane, {{chem2|(CH3CH2)(CH3)2N*AlH3}}) thermally decompose to give aluminium and may have use in [[MOCVD]] applications.<ref>{{cite journal | title = Metal-Organic Chemical Vapor Deposition of Aluminum from Dimethylethylamine Alane |author1=Yun, J.-H. |author2=Kim, B.-Y. |author3=Rhee, S.-W. | journal = Thin Solid Films | year = 1998 | volume = 312 | issue = 1–2 | pages = 259–263 | doi = 10.1016/S0040-6090(97)00333-7 |bibcode = 1998TSF...312..259Y}}</ref>

Its complex with [[diethyl ether]] forms according to the following stoichiometry:
:{{chem2|AlH3 + (CH3CH2)2O → (CH3CH2)2O*AlH3}}

The reaction with [[lithium hydride]] in ether produces [[lithium aluminium hydride]] (lithium alanate, lithium tetrahydridoaluminate):
:{{chem2|AlH3 + LiH → Li[AlH4]}}

Analogous alanates (e.g. {{chem|Na|3|Al|H|6}}, {{chem|Ca|(Al|H|4)|)|2}}, {{chem|Sr|Al|H|5}}) exist with other alkali alkaline earth and some other metals.<ref>{{cite journal | title = Alanates, a Comprehensive Review |author1=Suárez-Alcántara, Karina |author2=Tena-Garcia, Juan Rogelio |author3=Guerrero-Ortiz, Ricardo | journal = Materials | year = 2019 | volume = 12 | issue = 17 | pages = 2724 | doi = 10.3390/ma12172724|doi-access=free |pmid=31450714 |pmc=6747775 |bibcode=2019Mate...12.2724S }}</ref> {{chem|Li|3|Al|H|6}} is under investigation as a lithium ion cell anode material.

===Reduction of functional groups===
In organic chemistry, aluminium hydride is mainly used for the reduction of functional groups.<ref name = galatsis>{{cite encyclopedia | author = Galatsis, P. | encyclopedia = Encyclopedia of Reagents for Organic Synthesis | year = 2001 | doi = 10.1002/047084289X.rd245 | isbn = 978-0-470-84289-8 | chapter = Diisobutylaluminum Hydride}}</ref> In many ways, the reactivity of aluminium hydride is similar to that of [[lithium aluminium hydride]]. Aluminium hydride will reduce [[aldehyde]]s, [[ketone]]s, [[carboxylic acid]]s, [[anhydride]]s, [[acid chloride]]s, [[ester]]s, and [[lactone]]s to their corresponding [[Alcohol (chemistry)|alcohol]]s. [[Amide]]s, [[nitrile]]s, and [[oxime]]s are reduced to their corresponding [[amine]]s.

In terms of functional group selectivity, alane differs from other hydride reagents. For example, in the following cyclohexanone reduction, [[lithium aluminium hydride]] gives a trans:cis ratio of 1.9 : 1, whereas aluminium hydride gives a trans:cis ratio of 7.3 : 1.<ref>{{cite journal |author1=Ayres, D. C. |author2=Sawdaye, R. | title = The Stereoselective Reduction of Ketones by Aluminium Hydride | journal = Journal of the Chemical Society B | year = 1967 | volume = 1967 | pages = 581–583 | doi = 10.1039/J29670000581}}</ref>
[[File:Functional Group Reduction 1.svg|300px|center|Stereoselective reduction of a substituted cyclohexanone using aluminium hydride]]
Alane enables the hydroxymethylation of certain ketones (that is the replacement of {{chem2|C\sH}} by {{chem2|C\sCH2OH}} at the [[Alpha carbon|alpha position]]).<ref>{{cite journal |author1=Corey, E. J. |author2=Cane, D. E. | title = Controlled Hydroxymethylation of Ketones | journal = [[Journal of Organic Chemistry]] | year = 1971 | volume = 36 | issue = 20 | pages = 3070 | doi = 10.1021/jo00819a047}}</ref> The ketone itself is not reduced as it is "protected" as its enolate.

[[File:Functional Group Reduction 2.svg|300px|center|Functional Group Reduction using aluminium hydride]]
[[Organohalide]]s are reduced slowly or not at all by aluminium hydride. Therefore, reactive functional groups such as [[carboxylic acid]]s can be reduced in the presence of halides.<ref>{{cite journal |first=Margaret J.|last=Jorgenson|title=Selective reductions with aluminum hydride|journal=Tetrahedron Letters|volume=3|issue=13|pages=559–562|date=July 1962|doi=10.1016/S0040-4039(00)76929-2}}</ref>

[[File:Functional Group Reduction 3.svg|300px|center|Functional Group Reduction using aluminium hydride]]
[[Nitro group]]s are not reduced by aluminium hydride. Likewise, aluminium hydride can accomplish the reduction of an [[ester]] in the presence of nitro groups.<ref>{{cite journal | author1 = Takano, S. | author2 = Akiyama, M. | author3 = Sato, S. | author4 = Ogasawara, K. | title = A Facile Cleavage of Benzylidene Acetals with Diisobutylaluminum Hydride | journal = Chemistry Letters | year = 1983 | volume = 12 | issue = 10 | pages = 1593–1596 | doi = 10.1246/cl.1983.1593 | url = http://www.jstage.jst.go.jp/article/cl1972/12/10/12_10_1593/_pdf | format = pdf }}{{Dead link|date=March 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

[[File:Functional Group Reduction 4.svg|300px|center|Ester reduction using aluminium hydride]]
Aluminium hydride can be used in the reduction of acetals to half protected diols.<ref>{{cite journal | author = Richter, W. J. | title = Asymmetric Synthesis at Prochiral Centers: Substituted 1,3-Dioxolanes | journal = [[Journal of Organic Chemistry]] | year = 1981 | volume = 46 | issue = 25 | pages = 5119–5124 | doi = 10.1021/jo00338a011}}</ref>

[[File:Functional Group Reduction 5.svg|300px|center|Acetal reduction using aluminium hydride]]
Aluminium hydride can also be used in epoxide ring opening reaction as shown below.<ref>{{cite journal |author1=Maruoka, K. |author2=Saito, S. |author3=Ooi, T. |author4=Yamamoto, H. | title = Selective Reduction of Methylenecycloalkane Oxides with 4-Substituted Diisobutylaluminum 2,6-Di-''tert''-butylphenoxides | journal = Synlett | year = 1991 | volume = 1991 | issue = 4 | pages = 255–256 | doi = 10.1055/s-1991-20698|s2cid=196795254 }}</ref>

[[File:Epoxide Ring Opening.jpg|300px|center|Epoxide reduction using aluminium hydride]]
The allylic rearrangement reaction carried out using aluminium hydride is a [[SN2 reaction|S<sub>N</sub>2]] reaction, and it is not sterically demanding.<ref>{{cite journal |author1=Claesson, A. |author2=Olsson, L.-I. | title = Allenes and Acetylenes. 22. Mechanistic Aspects of the Allene-Forming Reductions (SN2' Reaction) of Chiral Propargylic Derivatives with Hydride Reagents | journal = [[Journal of the American Chemical Society]] | year = 1979 | volume = 101 | issue = 24 | pages = 7302–7311 | doi = 10.1021/ja00518a028}}</ref>

[[File:Allylic rearrangement reaction.svg|300px|center|Phosphine reduction using aluminium hydride]]
Aluminium hydride will reduce [[carbon dioxide]] to [[methane]] with heating:{{cn|date = July 2022}}
:{{chem2|4 AlH3 + 3 CO2 → 3 CH4 + 2 Al2O3}}

===Hydroalumination===
{{Needs expansion|date=July 2022}}
{{See also|Carbometalation#Carboalumination}}
Akin to [[hydroboration]], aluminium hydride can, in the presence of [[titanium tetrachloride]], add across [[multiple bond]]s.<ref>{{cite journal |author1=Sato, F. |author2=Sato, S. |author3=Kodama, H. |author4=Sato, M. | title = Reactions of Lithium Aluminum Hydride or Alane with Olefins Catalyzed by Titanium Tetrachloride or Zirconium Tetrachloride. A Convenient Route to Alkanes, 1-Haloalkanes and Terminal Alcohols from Alkenes | journal = [[Journal of Organometallic Chemistry]] | year = 1977 | volume = 142 | issue = 1 | pages = 71–79 | doi = 10.1016/S0022-328X(00)91817-5}}</ref><ref>Smith (2020), ''March's Advanced Organic Chemistry'', rxn.&nbsp;15-12.</ref>  When the multiple bond in question is a [[propargylic alcohol]]s, the results are [[Alkenylaluminium compounds]].<ref>{{cite journal |author1=Corey, E. J. |author2=Katzenellenbogen, J. A. |author3=Posner, G. H. | title = New Stereospecific Synthesis of Trisubstituted Olefins. Stereospecific Synthesis of Farnesol | journal = [[Journal of the American Chemical Society]] | year = 1967 | volume = 89 | issue = 16 | pages = 4245–4247 | doi = 10.1021/ja00992a065}}</ref> 
[[File:Hydroalumination.svg|300px|center|Hydroalumination of 1-hexene]]

===Fuel===
{{update|section |small = no | date = July 2022}}
In its passivated form, alane is an active candidate for storing hydrogen, and can be used for efficient power generation via fuel cell applications, including fuel cell and electric vehicles and other lightweight power applications.<ref name = Liu_SolidFuel >{{cite journal
| last1 = Liu
| first1 = Y.
| last2 = Yang
| first2 = F. 
| last3 = Zhang
| first3 = Y.
| last4 = Wu
| first4 = Z.
| last5 = Zhang
| first5 = Z.
| title = AlH3 as High-Energy Fuels for Solid Propellants: Synthesis, Thermodynamics, Kinetics, and Stabilization.
| journal = Compounds
| pages = 230–251
| date = 2024
| volume = 4
| issue = 2
| language = English
| doi= 10.3390/compounds4020012  
| doi-access = free
}}</ref>
{{chem2|AlH3}} contains up 10.1% hydrogen by weight (at a density of 1.48 grams per milliliter),<ref name = h2storage>{{cite report |author1=Graetz, J.. |author2=Reilly, J.. |author3=Sandrock, G.. |author4=Johnson, J.. |author5=Zhou, W.-M. |author6=Wegrzyn, J. | year= 2006 | title = Aluminum Hydride, A1H3, As a Hydrogen Storage Compound | url = https://www.osti.gov/biblio/899889-UGd8IT/ | location = Washington, D.C. | publisher = Office of Science and Technical Information [OSTI] | access-date = 28 July 2022 | doi = 10.2172/899889 | osti= 899889}}</ref> or twice the hydrogen density of liquid {{chem2|H2}}.{{cn|date = July 2022}} As of 2006, {{chem2|AlH3}} was  described as a candidate for which "further research w[ould] be required to develop an efficient and economical process to regenerate [it] from the spent Al powder".<ref name = h2storage/>{{update after|2022|7|29}}

Alane is also a potential additive to solid [[rocket fuel]] and to explosive and pyrotechnic compositions {{cn|date = July 2022}} due to its high hydrogen content and low dehydrogenation temperature.<ref name = Liu_SolidFuel/> In its unpassivated form, alane is also a promising [[rocket fuel]] additive, capable of delivering impulse efficiency gains of up to 10%.<ref>{{cite journal|last=Calabro|first=M.|date=2011|title=Overview of Hybrid Propulsion|journal=Progress in Propulsion Physics|volume=2|pages=353–374|bibcode=2011EUCAS...2..353C|doi=10.1051/eucass/201102353|isbn=978-2-7598-0673-7|doi-access=free}}</ref> However, {{chem2|AlH3}} can degrade when stored at room temperature, and some of its crystal forms have "poor compatibility" with some fuel components.<ref name = Liu_SolidFuel/>

===Deposition===
Heated alane releases hydrogen gas and produces a very fine thin film of aluminum metal.<ref name=HS5p401/>

== References ==
<references>
<ref name=EROSv08>{{cite book | last1= Galatsis |first1=P |last2=Sintim |first2=Herman&nbsp;O. |author3=Wang J. | date = 15 September 2008 | title = Encyclopedia of Reagents for Organic Synthesis |edition=online | chapter = Aluminum Hydride | location = New York, N.Y. | publisher = John Wiley & Sons | doi = 10.1002/047084289X.ra082.pub2 | isbn = 978-0471936237 | url = https://onlinelibrary.wiley.com/doi/10.1002/047084289X.ra082.pub2 | access-date = 28 July 2022 | url-access = subscription |ref={{harvid|Galatsis|Sintim|Wang|2008}} }}</ref>
<ref name=EROSv04>{{cite book | last1 = Paquette |first1=L.&nbsp;A. |last2=Ollevier |first2=T. |last3=Desyroy |first3=V. | date = 15 October 2004 | title = Encyclopedia of Reagents for Organic Synthesis |edition=online | chapter = Lithium Aluminum Hydride | location = New York, N.Y. | publisher = John Wiley & Sons | doi = 10.1002/047084289X.rl036.pub2 | isbn = 0471936235 | url = https://onlinelibrary.wiley.com/doi/10.1002/047084289X.rl036.pub2 | access-date = 28 July 2022}}</ref>
<ref name=Crystal>{{cite journal | title = The Crystal Structure of Aluminum Hydride |last1=Turley |first1=J.&nbsp;W. |last2=Rinn |first2=H.&nbsp;W. | journal = Inorganic Chemistry | year = 1969 | volume = 8 | issue = 1 | pages = 18–22 | doi = 10.1021/ic50071a005}}</ref> 
</references>

== External links ==
*[http://EnvironmentalChemistry.com/yogi/chemicals/cn/Aluminum%A0hydride.html Aluminium Hydride] on EnvironmentalChemistry.com Chemical Database
*[https://web.archive.org/web/20060823192048/http://www.bnl.gov/est/erd/hydrogenStorage/ Hydrogen Storage] from Brookhaven National Laboratory
*[http://www.webelements.com/compounds/aluminium/aluminium_trihydride.html Aluminum Trihydride] on WebElements

{{Aluminium compounds}}
{{Hydrides by group}}

{{Authority control}}

[[Category:Aluminium compounds]]
[[Category:Metal hydrides]]
[[Category:Reducing agents]]