Sodium cyanoborohydride

Sodium cyanoborohydride is the chemical compound with the formula Na[BH3(CN)]. 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
Sodium cyanoborohydride
Names
Other names
Sodium cyanotrihydridoborate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.043.001
EC Number
  • 247-317-2
UNII
  • InChI=1S/CH3BN.Na/c2-1-3;/h2H3;/q-1;+1
  • [BH3-]C#N.[Na+]
Properties
Na[BH3(CN)]
Molar mass 62.84 g·mol−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
Structure
4 at boron atom
Tetrahedral at boron atom
Hazards
Occupational safety and health (OHS/OSH):
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
GHS labelling:
GHS02: FlammableGHS05: CorrosiveGHS06: Toxic
Danger
H228, H300, H310, H314, H330, H410
P210, P260, P264, P273, P280, P284
NFPA 704 (fire diamond)
NFPA 704 four-colored diamond
4
3
2
5 mg/m3 (TWA)
Safety data sheet (SDS) Sigma Aldrich[1]
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).
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Infobox references

Use

Owing to the presence of the electron-withdrawing cyanide substituent, [BH3(CN)]− is less reducing than is [BH4]−.[3] As a mild reducing agent, it is used to convert imines to amines.[4]

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 + Na[BH3(CN)] + CH3OH → R2CH−NH−R' + "Na[BH2(CN)(OCH3)]" +H2O

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").[5]

In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones.[2]

Structure and preparation

The [BH3(CN)]− ion is tetrahedral at the boron atom, and it comprises the anionic component of the salt.

The reagent is often purchased, although it can be prepared easily. One method involves combining sodium cyanide and borane. Another route is treating sodium borohydride with mercury(II) cyanide. The commercial samples can be purified, but the yields of the reductive aminations do not improve.[6]

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. pp. rs059.pub2. doi:10.1002/047084289X.rs059.pub2. ISBN 978-0-471-93623-7.
  3. Baxter, Ellen W.; Reitz, Allen B. (9 January 2002). "Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents". Organic Reactions: 1–714. doi:10.1002/0471264180.or059.01. ISBN 0-471-26418-0.
  4. Christen, Hans; Meyer, Gerd (1997). Grundlagen der allgemeinen und anorganischen Chemie (1 ed.). Salle + Sauerländer. p. 824. ISBN 978-3-7935-5493-6.
  5. Richard F. Borch (1988). "Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine". Organic Syntheses.; Collective Volume, vol. 6, p. 499
  6. 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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