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Lithium borohydride

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Lithium borohydride Basic information
Lithium borohydride Chemical Properties
  • Melting point:280 °C
  • Boiling point:66°C/760mmHg
  • Density 0.896 g/mL at 25 °C
  • Flash point:−1 °F
  • storage temp. water-free area
  • solubility Soluble in ether, THF, and aliphatic aminesSoluble in ether, tetrahydrofuran, aliphatic amines and ethanol.
  • form Powder
  • color White
  • Specific Gravity0.66
  • explosive limit4.00-75.60%(V)
  • Water Solubility soluble H2O above pH 7, ether, tetrahydrofuran, aliphatic amines [MER06]
  • Sensitive Air & Moisture Sensitive
  • Merck 14,5525
  • CAS DataBase Reference16949-15-8(CAS DataBase Reference)
  • NIST Chemistry ReferenceLithium tetrahydroborate(16949-15-8)
  • EPA Substance Registry SystemBorate(1-), tetrahydro-, lithium (16949-15-8)
Safety Information
MSDS
Lithium borohydride Usage And Synthesis
  • Physical PropertiesWhite orthorhombic crystals; density 0.67 g/cm3; decomposes in moist air; melts at 268°C; decomposes at 380°C; reacts with water; dissolves in ether, tetrahydrofuran, and diethylamine; solubility in ether, 25g/L at 25°C.
  • UsesLithium borohydride is used as a strong reducing agent. Its principal applications are in organic syntheses for reducing carbonyl groups such as aldehydes, ketones, and esters. It also is used for selectively reducing a carbonyl group in the presence of a nitrile group. Such selective reduction cannot be achieved with lithium aluminum hydride, which is a much stronger reducing agent. The compound also is used to detect free carbonyl groups in proteins and peptides.
  • PreparationLithium borohydride is prepared by reacting ethyllithium with aluminum borohydride:
    C2H5Li + Al(BH4)3→3LiBH4 + Al(C2H5)3
    Alternatively, the compound may be obtained by the reaction of ethyllithium with diborane:
    C2H5Li + B2H6→LiBH4 + C2H5BH2
  • ReactionsLithium borohydride reacts with water with liberation of hydrogen:
    LiBH4 + 2H2O → LiBO2 + 4H2
    Reaction with methanol yields lithium boromethoxide and hydrogen:
    LiBH4 + 2CH3OH → LiB(OCH3)2 + 3H2
    Reaction with hydrogen chloride yields diborane, lithium chloride and hydrogen:
    2LiBH4 + 2HCl → 2LiCl + B2H6 + 2H2
    Reactions with oxidizing agents are violent.
  • Chemical PropertiesWHITE POWDER
  • Physical propertiesWhite orthorhombic crystals; density 0.67 g/cm3; decomposes in moist air; melts at 268°C; decomposes at 380°C; reacts with water; dissolves in ether, tetrahydrofuran, and diethylamine; solubility in ether, 25g/L at 25°C.
  • UsesStrong reducing agent. Used in the reduction of Compounds contg ketonic, aldehydic, or ester carbonyls and a nitrile group, where reduction of the carbonyl, but not of the nitrile group, is wanted. In the determination of free carboxyl groups in peptides and proteins; after esterification and acetylation, only the ester groups, and none of the peptide bonds are reduced.
  • General DescriptionA white to grayish crystalline powder.
  • Air & Water ReactionsLikely to ignite when moistened with water [Lab. Gov. Chemist 1965].
  • Reactivity ProfileLithium borohydride is a strong reducing agent. Is easily ignited and burns vigorously once ignited. Reacts on contact with water or acids to form hydrogen gas and corrosive products. Reaction with limited amounts of water or moisture may cause ignition after a delay [Gaylord, 1965, p. 22].
  • Health HazardInhalation or contact with vapors, substance or decomposition products may cause severe injury or death. May produce corrosive solutions on contact with water. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control may cause pollution.
  • Fire HazardProduce flammable gases on contact with water. May ignite on contact with water or moist air. Some react vigorously or explosively on contact with water. May be ignited by heat, sparks or flames. May re-ignite after fire is extinguished. Some are transported in highly flammable liquids. Runoff may create fire or explosion hazard.
  • Safety ProfilePoison by ingestion, inhalation, and skin contact. Flammable; can liberate H2. Incompatible with H20 as moisture on fibers of cellulose or as liquid. See also LITHIUM, BORON COMPOUNDS, and HYDRIDES.
  • Purification MethodsIt is crystallised from Et2O, and pumped free of ether at 90-100o during 2hours [Schaeffer et al. J Am Chem Soc 78 729 1956]. Store it dry as it decomposes slowly in moist air. [Becher in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 775 1963.]
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