氢化铝锂：修订间差异

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氢化铝锂具有[[单斜]]的晶体结构，AlH<sub>4</sub><sup>−</sup>离子为[[四面体]]结构。氢化铝锂中，Li<sup>+</sup> 与五个氢相邻，其中四个的距离为 1.88-2.00Å，与第五个氢的距离稍长，为 2.16Å<ref>F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann, ''Advanced Inorganic Chemistry'', 6th ed.. Wiley-Interscience. ISBN 0-471-19957-5.</ref>。其[[晶胞]]参数为：a = 4.82，b = 7.81，c = 7.92 Å，α = γ = 90° 和 β = 112°。
氢化铝锂具有[[单斜]]的晶体结构，AlH<sub>4</sub><sup>−</sup>离子为[[四面体]]结构。氢化铝锂中，Li<sup>+</sup> 与五个氢相邻，其中四个的距离为 1.88-2.00Å，与第五个氢的距离稍长，为 2.16Å<ref>F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann, ''Advanced Inorganic Chemistry'', 6th ed.. Wiley-Interscience. ISBN 0-471-19957-5.</ref>。其[[晶胞]]参数为：a = 4.82，b = 7.81，c = 7.92 Å，α = γ = 90° 和 β = 112°。


==Solubility data==
==溶解度==
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==热力学==
==Thermodynamic data==
The table summarizes [[thermodynamics|thermodynamic]] data for LAH and reactions involving LAH,<ref name="InorganicHandbook" /><ref>{{cite journal|doi=10.1021/je60018a020|title=Heats and Free Energies of Formation of the Alkali Aluminum Hydrides and of Cesium Hydride.|year=1963|last1=Smith|first1=Martin B.|last2=Bass|first2=George E.|journal=Journal of Chemical & Engineering Data|volume=8|pages=342}}</ref> in the form of [[Standard state|standard]] [[enthalpy]], [[entropy]] and [[Gibbs free energy]] change, respectively.
The table summarizes [[thermodynamics|thermodynamic]] data for LAH and reactions involving LAH,<ref name="InorganicHandbook" /><ref>{{cite journal|doi=10.1021/je60018a020|title=Heats and Free Energies of Formation of the Alkali Aluminum Hydrides and of Cesium Hydride.|year=1963|last1=Smith|first1=Martin B.|last2=Bass|first2=George E.|journal=Journal of Chemical & Engineering Data|volume=8|pages=342}}</ref> in the form of [[Standard state|standard]] [[enthalpy]], [[entropy]] and [[Gibbs free energy]] change, respectively.


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==热分解==
==Thermal decomposition==
LAH is [[Metastability in molecules|metastable]] at room temperature. During prolonged storage it slowly decomposes to Li<sub>3</sub>AlH<sub>6</sub> and LiH.<ref name="Dymova">{{cite journal|author=Dymova T. N.; Aleksandrov, D. P.; Konoplev, V. N.; Silina,T. A.; Sizareva; A. S.|journal=Russ. J. Coord. Chem.|volume= 20|page=279|year=1994}}</ref> This process can be accelerated by the presence of [[catalysis|catalytic]] elements, such as [[titanium]], [[iron]] or [[vanadium]].
LAH is [[Metastability in molecules|metastable]] at room temperature. During prolonged storage it slowly decomposes to Li<sub>3</sub>AlH<sub>6</sub> and LiH.<ref name="Dymova">{{cite journal|author=Dymova T. N.; Aleksandrov, D. P.; Konoplev, V. N.; Silina,T. A.; Sizareva; A. S.|journal=Russ. J. Coord. Chem.|volume= 20|page=279|year=1994}}</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 LiAlH<sub>4</sub>.]]
[[File:Lialh4 dsc.svg|thumb|[[Differential scanning calorimetry]] of as-received LiAlH<sub>4</sub>.]]
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::LiAlH<sub>4</sub> + 3ROH → LiAl(OR)<sub>3</sub>H + 3H<sub>2</sub>
::LiAlH<sub>4</sub> + 3ROH → LiAl(OR)<sub>3</sub>H + 3H<sub>2</sub>
LiAl(OR)<sub>2</sub>H<sub>2</sub> 是将[[酰胺]]还原为[[醛]]的适宜试剂，LiAl(OC(CH<sub>3</sub>)<sub>3</sub>)<sub>3</sub>H 是将[[酰氯]]还原为[[醛]]的适宜试剂<ref name="无机化学丛书"/>。
LiAl(OR)<sub>2</sub>H<sub>2</sub> 是将[[酰胺]]还原为[[醛]]的适宜试剂，LiAl(OC(CH<sub>3</sub>)<sub>3</sub>)<sub>3</sub>H 是将[[酰氯]]还原为[[醛]]的适宜试剂<ref name="无机化学丛书"/>。

===储氢===
[[File:volvsgrav.png|300px|thumb|不同储氢方式的容积和种类储氢密度，金属氢化物用方框表示，复合氢化物用三角形表示（包括LiAlH<sub>4</sub>）。上述值不包括容器质量，而[[美國能源部]][[FreedomCAR]]目标包含容器质量。]]
LiAlH<sub>4</sub> 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 NaAlH<sub>4</sub>,<ref>{{cite journal|doi=10.1016/S0925-8388(96)03049-6|year=1997|last1=Bogdanovic|first1=B|last2=Schwickardi|first2=M|journal=Journal of Alloys and Compounds|volume=253-254|pages=1|title=Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials}}</ref> have sparkled renewed research into LiAlH<sub>4</sub> 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|last2=Czujko|first2=T|last3=Wronski|first3=Z S|title=Nanomaterials for Solid State Hydrogen Storage|publisher=Springer|year=2009|edition=5th|pages=338|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 °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 LiAlH<sub>4</sub> which, due 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 Li<sub>3</sub>AlH<sub>6</sub> as starting material, would store 5.6 wt% hydrogen in a single step (vs. two steps for NaAlH<sub>4</sub> which stores about the same amount of hydrogen). However, attempts on this have not been successful so far.


== 参见 ==
== 参见 ==
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*[[氢化铝]]
*[[氢化铝]]


== 参考资料 ==
== 参考文献 ==
{{reflist}}
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2010年9月9日 (四) 03:30的版本

氢化铝锂
结构式
晶胞球棍模型
IUPAC名
Lithium aluminium hydride
别名 LAH，氢化锂铝
四氢铝锂
四氢合铝酸锂
识别
CAS号 16853-85-3
RTECS BD0100000
性质
化学式 LiAlH4
摩尔质量 37.95 g·mol⁻¹
外观 白色晶体（纯时）
灰色粉末（工业品）
密度 0.917
熔点 150°C 分解
溶解性（水） 反应
结构
晶体结构 单斜
危险性
主要危害 高度易燃
NFPA 704
2
3
2
W
相关物质
相关氢化物 氢化铝
硼氢化钠
氢化钠
若非注明，所有数据均出自标准状态（25 ℃，100 kPa）下。

氢化铝锂（Lithium Aluminium Hydride）是一个复合氢化物，分子式为LiAlH4。氢化铝锂缩写为LAH，是有机合成中非常重要的还原剂。纯的氢化铝锂是白色晶状固体，在120°C以下和干燥空气中相对稳定，但遇水即爆炸性分解。

制备

1947年，H. I. Schlessinger，H. C. Brown和A. E. Finholt首次制得氢化铝锂，其方法是令氢化锂与无水三氯化铝在乙醚中进行反应[1]：

4LiH + AlCl3 −Et2O→ LiAlH4 + 3LiCl

这个反应一般称为 Schlessinger 反应，反应产率以三氯化铝计算为86%。反应开始时要加入少量氢化铝锂作为引发剂，否则反应要经历一段诱导期才能发生，并且一旦开始后会以猛烈的速度进行，容易发生事故[2]。

Schlessinger 法有很多缺点，如需要用引发剂、氢化锂要求过量和高度粉细、需要用稀缺的原料金属锂、反应中3/4的氢化锂转化为价廉的氯化锂等[2]。虽然如此，相对于其他方法，Schlessinger 法较简便，至今仍是制取氢化铝锂的主要方法。

其他制取氢化铝锂的方法包括[2]：

LiH + Al + 3/2 H2 → LiAlH4
Na + Al + 2H2 → NaAlH4
NaAlH4 + LiCl −Et2O→ LiAlH4 + NaCl

结构

氢化铝锂具有单斜的晶体结构，AlH4−离子为四面体结构。氢化铝锂中，Li+ 与五个氢相邻，其中四个的距离为 1.88-2.00Å，与第五个氢的距离稍长，为 2.16Å[4]。其晶胞参数为：a = 4.82，b = 7.81，c = 7.92 Å，α = γ = 90° 和 β = 112°。

溶解度

Solubility of LiAlH4 (mol/L)[5]
Temperature (°C)
Solvent 0 25 50 75 100
Diethyl ether – 5.92 – – –
THF – 2.96 – – –
Monoglyme 1.29 1.80 2.57 3.09 3.34
Diglyme 0.26 1.29 1.54 2.06 2.06
Triglyme 0.56 0.77 1.29 1.80 2.06
Tetraglyme 0.77 1.54 2.06 2.06 1.54
Dioxane – 0.03 – – –
Dibutyl ether – 0.56 – – –

LAH is soluble in many etheral 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.[5]

热力学

The table summarizes thermodynamic data for LAH and reactions involving LAH,[6][7] in the form of standard enthalpy, entropy and Gibbs free energy change, respectively.

Thermodynamic data for reactions involving LiAlH4
Reaction ΔH°
(kJ/mol)		 ΔS°
(J/(mol·K))		 ΔG°
(kJ/mol)		 Comment
Li (s) + Al (s) + 2 H2(g) → LiAlH4 (s) −116.3 −240.1 −44.7 Standard formation from the elements.
LiH (s) + Al (s) + 3/2 H2 (g) → LiAlH4 (s) −25.6 −170.2 23.6 Using ΔH°f(LiH) = −90.5, ΔS°f(LiH) = −69.9, and ΔG°f(LiH) = −68.3.
LiAlH4 (s) → LiAlH4 (l) 22 – – Heat of fusion. Value might be unreliable.
LiAlH4 (l) → ⅓ Li3AlH6 (s) + ⅔ Al (s) + H2 (g) 3.46 104.5 −27.68 ΔS° calculated from reported values of ΔH° and ΔG°.

热分解

LAH is metastable at room temperature. During prolonged storage it slowly decomposes to Li3AlH6 and LiH.[8] This process can be accelerated by the presence of catalytic elements, such as titanium, iron or vanadium.

Differential scanning calorimetry of as-received LiAlH4.

When heated LAH decomposes in a three-step reaction mechanism:[8][9][10]

3 LiAlH4 → Li3AlH6 + 2 Al + 3 H2 (R1)
2 Li3AlH6 → 6 LiH + 2 Al + 3 H2 (R2)
2 LiH + 2 Al → 2 LiAl + H2 (R3)

R1 is usually initiated by the melting of LAH in the temperature range 150–170 °C [11][12][13], immediately followed by decomposition into solid Li3AlH6, although R1 is known to proceed below the melting point of LiAlH4 as well.[14] At about 200 °C, Li3AlH6 decomposes into LiH (R2)[8][10][13] and Al which subsequently convert into LiAl above 400 °C (R3) [10]. Reaction R1 is effectively irreversible. R3 is reversible with an equilibrium pressure of about 0.25 bar at 500 °C. R1 and R2 can occur at room temperature with suitable catalysts.[15]

反应

LiAlH4遇水立即发生爆炸性的猛烈反应并放出氢气：

LiAlH4 + 2H2O → LiAlO2 + 4H2
LiAlH4 + 4H2O → LiOH + Al(OH)3 + 4H2

由于放出的氢是定量的，该反应可用来测定样品中氢化铝锂的含量。为了防止反应过于剧烈，常加入一些二噁烷、二甲基乙二醇醚或四氢呋喃作为稀释剂[2]。

LiAlH4 的乙醚或四氢呋喃溶液能同氨猛烈作用放出氢气：

2LiAlH4 + 5NH3 → [LiAlH(NH2)2]2NH + 6H2

当氨的量不足时，发生如下反应：

LiAlH4 + 4NH3 → LiAl(NH2)4 + 2H2

NH3/LiAlH4比值更小时，则氨中的三个氢都可被取代。

  • 合成其他复合氢化物或简单氢化物：

氢化铝锂几乎可以与所有的卤化物反应生成相应的配位铝氢化物，当配位铝氢化物不稳定时，则分解为相应的氢化物。通式为：

nLiAlH4 + MXn → M(AlH4)n + nLiX
M(AlH4)n → MHn + nAlH3

因此可通过此方法制备很多金属或非金属氢化物，如：

2LiAlH4 + ZnI2 −(-40℃，乙醚)→ ZnH2 + 2AlH3 + 2LiI
  • 作为还原剂：

氢化铝锂可将很多有机化合物还原[16]，实际中常用其乙醚或四氢呋喃溶液。由于存储和使用不方便，工业上常用氢化铝锂的衍生物双(2-甲氧基乙氧基)氢化铝钠（红铝）作为还原剂。

Organic reactions of lithium aluminium hydride

能被氢化铝锂还原的官能团主要包括：

    • 卤代烃被还原成烃。此反应中一级卤代烃性能较好，所得产物发生构型转化，因此认为该反应是SN2机理。二级卤代烃也可用此法还原，三级卤代烃容易发生消除反应，不适用此法[17]。
    • 硅卤化物等还原为硅烷[2]，如：
LiAlH4 + SiCl4 → SiH4 + LiCl + AlCl3
LiAlH4 + ROH → LiAl(OR)H3 + H2
LiAlH4 + 2ROH → LiAl(OR)2H2 + 2H2
LiAlH4 + 3ROH → LiAl(OR)3H + 3H2

LiAl(OR)2H2 是将酰胺还原为醛的适宜试剂，LiAl(OC(CH3)3)3H 是将酰氯还原为醛的适宜试剂[2]。

储氢

不同储氢方式的容积和种类储氢密度，金属氢化物用方框表示，复合氢化物用三角形表示（包括LiAlH4）。上述值不包括容器质量，而美國能源部FreedomCAR目标包含容器质量。

LiAlH4 contains 10.6 wt% hydrogen thereby making LAH a potential hydrogen storage medium for future fuel cell powered vehicles. The high hydrogen content, as well as the discovery of reversible hydrogen storage in Ti-doped NaAlH4,[21] have sparkled 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 milling.[22] 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 °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, due to its relatively low stability, requires an extremely high hydrogen pressure in excess of 10000 bar.[22] 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 on this have not been successful so far.

参见

参考文献

  1. ^ A. E. Finholt, A. C. Bond, and H. I. Schlesinger, "Lithium Aluminum Hydride, Aluminum Hydride and Lithium Gallium Hydride, and Some of their Applications in Organic and Inorganic Chemistry" J. Am. Chem. Soc., 1947, volume 69, pp 1199 - 1203; doi: 10.1021/ja01197a061.
  2. ^ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 张青莲等。《无机化学丛书》第一卷。北京：科学出版社。
  3. ^ Holleman, A. F., Wiberg, E., Wiberg, N. (2007). Lehrbuch der Anorganischen Chemie, 102nd ed.. de Gruyter. ISBN 978-3-11-017770-1.
  4. ^ F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann, Advanced Inorganic Chemistry, 6th ed.. Wiley-Interscience. ISBN 0-471-19957-5.
  5. ^ 5.0 5.1 Mikheeva, V. I.; Troyanovskaya, E. A. Solubility of lithium aluminum hydride and lithium borohydride in diethyl ether. Bulletin of the Academy of Sciences of the USSR Division of Chemical Science. 1971, 20: 2497. doi:10.1007/BF00853610. 
  6. ^ 引用错误：没有为名为InorganicHandbook的参考文献提供内容
  7. ^ Smith, Martin B.; Bass, George E. Heats and Free Energies of Formation of the Alkali Aluminum Hydrides and of Cesium Hydride.. Journal of Chemical & Engineering Data. 1963, 8: 342. doi:10.1021/je60018a020. 
  8. ^ 8.0 8.1 8.2 Dymova T. N.; Aleksandrov, D. P.; Konoplev, V. N.; Silina,T. A.; Sizareva; A. S. Russ. J. Coord. Chem. 1994, 20: 279.  缺少或|title=为空 (帮助)
  9. ^ Dilts, J. A.; Ashby, E. C. Thermal decomposition of complex metal hydrides. Inorganic Chemistry. 1972, 11: 1230. doi:10.1021/ic50112a015. 
  10. ^ 10.0 10.1 10.2 Blanchard, D; Brinks, H; Hauback, B; Norby, P. Desorption of LiAlH4 with Ti- and V-based additives. Materials Science and Engineering B. 2004, 108: 54. doi:10.1016/j.mseb.2003.10.114. 
  11. ^ Chen, Jun; Kuriyama, Nobuhiro; Xu, Qiang; Takeshita, Hiroyuki T.; Sakai, Tetsuo. Reversible Hydrogen Storage via Titanium-Catalyzed LiAlH4and Li3AlH6. The Journal of Physical Chemistry B. 2001, 105: 11214. doi:10.1021/jp012127w. .
  12. ^ Balema, V. Solid state phase transformations in LiAlH4 during high-energy ball-milling. Journal of Alloys and Compounds. 2000, 313: 69. doi:10.1016/S0925-8388(00)01201-9. 
  13. ^ 13.0 13.1 Andreasen, A. Effect of Ti-doping on the dehydrogenation kinetic parameters of lithium aluminum hydride. Journal of Alloys and Compounds. 2006, 419: 40. doi:10.1016/j.jallcom.2005.09.067. 
  14. ^ Andreasen, A; Pedersen, A S; Vegge, T. Dehydrogenation kinetics of as-received and ball-milled LiAlH4. Journal of Solid State Chemistry. 2005, 178: 3672. doi:10.1016/j.jssc.2005.09.027. 
  15. ^ Balema, V; Wiench, J. W.; Dennis, K. W.; Pruski, M.; Pecharsky, V. K. Titanium catalyzed solid-state transformations in LiAlH4 during high-energy ball-milling. Journal of Alloys and Compounds. 2001, 329: 108. doi:10.1016/S0925-8388(01)01570-5. 
  16. ^ Brown, H. C. Org. React. 1951, 6, 469. (Review)
  17. ^ 邢其毅等。《基础有机化学》第三版上册。北京：高等教育出版社，2005年。ISBN 7-04-016637-2
  18. ^ Reetz, M. T.; Drewes, M. W.; Schwickardi, R. Organic Syntheses, Coll. Vol. 10, p.256 (2004); Vol. 76, p.110 (1999). (Article)
  19. ^ Oi, R.; Sharpless, K. B. Organic Syntheses, Coll. Vol. 9, p.251 (1998); Vol. 73, p.1 (1996). (Article)
  20. ^ Koppenhoefer, B.; Schurig, V. Organic Syntheses, Coll. Vol. 8, p.434 (1993); Vol. 66, p.160 (1988). (Article)
  21. ^ Bogdanovic, B; Schwickardi, M. Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials. Journal of Alloys and Compounds. 1997,. 253-254: 1. doi:10.1016/S0925-8388(96)03049-6. 
  22. ^ 22.0 22.1 Varin, R A; Czujko, T; Wronski, Z S. Nanomaterials for Solid State Hydrogen Storage 5th. Springer. 2009: 338. ISBN 978-0-387-77711-5. 

延伸阅读

  • Wiberg, Egon & Amberger, Eberhard. Hydrides of the elements of main groups I-IV. Elsevier. 1971. ISBN 0-444-40807-X. 
  • Hajos, Andor. Complex Hydrides and Related Reducing Agents in Organic Synthesis. Elsevier. 1979. ISBN 0-444-99791-1. 
  • Lide (ed.), David R. Handbook of chemistry and physics. CRC Press. 1997. ISBN 0-8493-0478-4. 
  • Carey, Francis A. Organic Chemistry with Online Learning Center and Learning by Model CD-ROM. McGraw-Hill. 2002. ISBN 0-07-252170-8.  on-line version
  • Chapter 5 in Andreasen, Anders. Hydrogen Storage Materials with Focus on Main Group I-II Elements. Risoe National Laboratory. 2005. ISBN 87-550-3498-5.  Full text version

外部链接

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