Sodium cyanoborohydride

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Sodium cyanoborohydride
Sodium cyanoborohydride
Identifiers
CAS number 25895-60-7 YesY
PubChem 20587905
EC number 247-317-2
Jmol-3D images Image 1
Properties
Molecular formula NaBH3CN
Molar mass 62.84 gmol-1
Appearance white to off-white powder, hygroscopic
Density 1.20 g/cm3
Melting point 241 °C (466 °F; 514 K) decomp
Solubility in water 212 g/100 mL (29 °C)
Solubility soluble in diglyme, tetrahydrofuran, methanol
slightly soluble in methanol
insoluble in diethyl ether
Hazards
MSDS Sigma Aldrich[1]
GHS pictograms GHS-pictogram-flamme.svgGHS-pictogram-acid.svgGHS-pictogram-skull.svg
GHS signal word Danger
GHS hazard statements H228, H300, H310, H330, H314, H410
GHS precautionary statements P210, P260, P264, P273, P280, P284
EU Index not listed
Main hazards Fatal if swallowed, in contact with skin or if inhaled
Contact with acids liberates very toxic gas
Contact with water liberates highly flammable gas
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 4: Very short exposure could cause death or major residual injury. E.g., VX gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus NFPA 704 four-colored diamond
Threshold Limit Value 5 mg/m3 (TWA)
Related compounds
Other anions Sodium borohydride
Related compounds Lithium aluminium hydride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Sodium cyanoborohydride is the chemical compound with the formula NaBH3CN. It is a colourless salt, but commercial samples can appear tan. It is widely used in organic synthesis for the reduction of imines. The salt tolerates aqueous conditions.[2]

Use[edit]

Owing to the presence of the electron-withdrawing cyanide substituent, [B(CN)H3] is far less reducing than is [BH4], as found in sodium borohydride.[3] As a mild reducing agent, it is especially used to convert imines to amines.

It is especially favored for reductive aminations, wherein aldehydes or ketones are treated with an amine in the presence of this reagent:

R2CO + R'NH2 + NaBH3CN + CH3OH → R2CH-NHR' + "NaCH3OBH2CN"

The reagent is typically used in excess. Selectivity is achieved at mildly basic solutions (pH 7-10). The reagent is ideal for reductive aminations ("Borch Reaction").[4] In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones.[2]

Structure and preparation[edit]

The tetrahedral anion BH3(CN) comprises the salt.

The reagent is invariably purchased, although it can be prepared easily. One method involves combining sodium cyanide and borane. Another route entails treating sodium borohydride with mercury(II) cyanide. The commercial samples can be purified but the yields of the reductive aminations do not improve.[5]

References[edit]

  1. ^ Sigma-Aldrich Co., Sodium cyanoborohydride. Retrieved on 2014-11-09.
  2. ^ a b Robert O. Hutchins, MaryGail K. Hutchins, Matthew L. Crawley "Sodium Cyanoborohydride" Encyclopedia of Reagents for Organic Synthesis, 2007 John Wiley & Sons. doi:10.1002/047084289X.rs059.pub2
  3. ^ Ellen W. Baxter, Allen B. Reitz Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents in Organic Reactions, 2002, John Wiley and Sons. doi:10.1002/0471264180.or059.01
  4. ^ Richard F. Borch (1988), "Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine", Org. Synth. ; Coll. Vol. 6: 499 
  5. ^ Richard F. Borch and Mark D. Bernstein and H. Dupont Durst (1971). "Cyanohydridoborate Anion as a Selective Reducing Agent". J. Am. Chem. Soc. 93 (12): 2897–2904. doi:10.1021/ja00741a013. 

See Also[edit]

Sodium triacetoxyborohydride - a milder reductant and a less toxic alternative, but highly unstable in water