Sodium cyanoborohydride

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]

Sodium cyanoborohydride
Names
Other names
Sodium cyanotrihydridoborate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.043.001
EC Number
  • 247-317-2
Properties
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) decomposes
212 g/100 mL (29 °C)
Solubility soluble in diglyme, tetrahydrofuran, methanol
slightly soluble in methanol
insoluble in diethyl ether
Hazards
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
Safety data sheet Sigma Aldrich[1]
GHS pictograms
GHS Signal word Danger
H228, H300, H310, H330, H314, H410
P210, P260, P264, P273, P280, P284
NFPA 704 (fire diamond)
3
4
2
5 mg/m3 (TWA)
Related compounds
Other anions
Sodium borohydride
Related compounds
Lithium aluminium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)
Infobox references

Use

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

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]

See also

References

  1. Sigma-Aldrich Co., Sodium cyanoborohydride. Retrieved on 2014-11-09.
  2. Robert O. Hutchins, MaryGail K. Hutchins, Matthew L. Crawley (2007). "Sodium Cyanoborohydride". Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rs059.pub2.CS1 maint: uses authors parameter (link)
  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". Organic Syntheses.; Collective Volume, 6, p. 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.
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