Lithium borohydride
| Lithium borohydride | |
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Lithium tetrahydridoborate(1–) |
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Other names
Lithium hydroborate, |
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| Identifiers | |
| CAS number | 16949-15-8  |
| PubChem | 4148881 |
| ChemSpider | 55732 |
| RTECS number | ED2725000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | LiBH4 |
| Molar mass | 21.784 g/mol |
| Appearance | White solid |
| Density | 0.666 g/cm3[1] |
| Melting point |
275 °C[1] |
| Boiling point |
380 °C (decomp) |
| Solubility in water | reacts |
| Solubility in ether | 2.5 g/100 mL |
| Thermochemistry | |
| Std enthalpy of formation ΔfH |
-8.759 kJ/g |
| Specific heat capacity, C | 3.792 J/g K |
| Hazards | |
| Autoignition temperature |
> 180 °C |
 (verify) (what is:  / ?)Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Lithium borohydride (LiBH4) is a tetrahydroborate and known in organic synthesis as a reducing agent for esters. Although less common than the related sodium borohydride, the lithium salt offers some advantages of being highly soluble in ethers and being a stronger reducing agent but still safer to handle than lithium aluminium hydride.
Contents |
Preparation [edit]
Lithium borohydride may be prepared by the metathesis reaction, which occurs upon ball-milling the more commonly available sodium borohydride, and lithium bromide:[2]
- NaBH4 + LiBr → NaBr + LiBH4
Reactions [edit]
Lithium borohydride reacts largely like sodium borohydride, in that it is a hydride-donating reducing agent in organic synthesis. It is however a stronger reducing agent. Unlike the sodium salt, lithium borohydride reduces esters and amides to the corresponding alcohols and amines.
Energy storage [edit]
Lithium borohydride is renowned as one of the highest energy density chemical energy carriers. Although presently of no practical importance, the solid will liberate 65 MJ/kg heat upon treatment with atmospheric oxygen. Since it has a density of 0.67 g/cm3, oxidation of liquid lithium borohydride gives 43 MJ/L. In comparison, gasoline gives 44 MJ/kg (or 35 MJ/L), while liquid hydrogen gives 120 MJ/kg (or 8.0 MJ/L).[nb 1] The high specific energy density of lithium borohydride has made it an attractive candidate to propose for automobile and rocket fuel, but despite the research and advocacy it has not been used widely. As with all chemical-hydride-based energy carriers, lithium borohydride is very complex to recycle (i.e. recharge) and therefore suffers from a low energy conversion efficiency. While batteries such as lithium ion carry an energy density of up to 0.72 MJ/kg and 2.0 MJ/L, their DC to DC conversion efficiency can be as high as 90%[citation needed]. In view of the complexity of recycling mechanisms for metal hydrides,[3] such high energy conversion efficiencies are beyond practical reach.
| Substance | Specific energy MJ/kg | Density g/cm3 | Energy density MJ/L |
|---|---|---|---|
| LiBH4 | 65.2 | 0.666 | 43.4 |
| Regular Gasoline | 44 | 0.72 | 34.8 |
| Liquid Hydrogen | 120 | 0.0708 | 8 |
| lithium ion battery | 0.72 | 2.8 | 2 |
See also [edit]
Notes [edit]
- ^ The greater ratio of energy density to specific energy for hydrogen is because of the very low mass density (0.071 g/cm3).
References [edit]
- ^ a b Sigma-Aldrich Product Detail Page
- ^ Peter Rittmeyer, Ulrich Wietelmann “Hydrides” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a13_199
- ^ US Patent 4002726 (1977) lithium borohydride recycling from lithium borate via a methyl borate intermediate
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