Lithium borohydride

Lithium borohydride

Names
IUPAC name Lithium tetrahydridoborate(1–)
Other names Lithium hydroborate, Lithium tetrahydroborate Borate(1-), tetrahydro-, lithium, lithium boranate
Identifiers
CAS Number	16949-15-8 Y
3D model (Jmol)	Interactive image
ChemSpider	55732 Y
ECHA InfoCard	100.037.277
PubChem	4148881
RTECS number	ED2725000
InChI InChI=1S/BH4.Li/h1H4;/q-1;+1 Y Key: UUKMSDRCXNLYOO-UHFFFAOYSA-N Y InChI=1/BH4.Li/h1H4;/q-1;+1 Key: UUKMSDRCXNLYOO-UHFFFAOYAS
SMILES [Li+].[BH4-]
Properties
Chemical formula	LiBH4
Molar mass	21.784 g/mol
Appearance	White solid
Density	0.666 g/cm3
Melting point	268 °C (514 °F; 541 K)
Boiling point	380 °C (716 °F; 653 K) decomposes
Solubility in water	reacts
Solubility in ether	2.5 g/100 mL
Thermochemistry
Specific heat capacity (C)	82.6 J/mol K
Std molar entropy (So298)	75.7 J/mol K
Std enthalpy of formation (ΔfHo298)	-198.83 kJ/mol
Hazards
Autoignition temperature	> 180 °C (356 °F; 453 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
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, being a stronger reducing agent and highly soluble in ethers, whilst remaining safer to handle than lithium aluminium hydride.

Lithium borohydride may be prepared by the metathesis reaction, which occurs upon ball-milling the more commonly available sodium borohydride, and lithium bromide:

Alternatively it may be synthesized by treating boron trifluoride with lithium hydride in diethyl ether:

Lithium borohydride is a stronger reducing agent than sodium borohydride. In mixtures of methanol and diethyl ether, lithium borohydride is able to reduce esters to alcohols and primary amides to amines. In contrast, these substrates are unaffected by sodium borohydride. The enhanced reactivity is attributed to the polarization of the carbonyl substrate by complexation to the lithium cation.

The use of lithium borohydride is particularly advantageous in some preparations due to its higher chemoselectivity relative to other popular reducing agents such as lithium aluminium hydride. For instance, unlike lithium aluminium hydride, lithium borohydride will reduce esters, nitriles, lactones, primary amides, and epoxides while sparing nitro groups, carbamic acids, alkyl halides, and secondary/tertiary amides.