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Sodium cyanoborohydride

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This is an old revision of this page, as edited by DMacks (talk | contribs) at 05:21, 8 December 2023 (→Uses: Overly specific, as it suggests the reagent always gives this result. It only does if there are no existing stereocenters and the C=O/C=N carbon is prochiral, etc.). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

Sodium cyanoborohydride
Line-bond structure of sodium cyanoborohydride
Image of sodium cyanoborohydride powder
Image of sodium cyanoborohydride powder
Names
IUPAC name
Sodium cyanoboranuide
Other names
Sodium cyanotrihydridoborate
Identifiers
3D model (JSmol)
ECHA InfoCard 100.043.001 Edit this at Wikidata
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 powder, hygroscopic
Density 1.083 g/cm (25°C)3
Melting point 242 °C (468 °F; 515 K) decomposes
212 g/(100 mL) (29 °C)
Solubility soluble in water, ethanol, 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
 Flammable solid, 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 diamondHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 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. gasolineInstability 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
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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Sodium cyanoborohydride is a chemical compound with the formula Na[BH3(CN)]. It is a colourless salt used in organic synthesis for chemical reduction including that of imines and carbonyls. Sodium cyanoborohydride is a milder reductant than other conventional reducing agents.[2]

Structure

Sodium cyanoborohydride is a salt. The cationic sodium ion, [Na]+, interacts with the anioniccyanoborohydride ion, [BH3(CN)]−. The anionic component of the salt is tetrahedral at the boron atom.

The electron-withdrawing cyanide substituent draws electron density away from the negatively charged boron; thus, reducing the electrophilic capabilities of the anionic component.[2] This electronic phenomenon causes sodium cyanoborohydride to have more mild reducing qualities than other reducing agents. For example, Na[BH3(CN)] is less reducing than its counterpart sodium borohydride, containing [BH4]−.[2]

Uses

Sodium cyanoborohydride is a mild reducing agent. It is often used for the reduction of imines and carbonyls.

Reduction of Imines

Imines can be reduced to amines using sodium cyanoborohydride.

Imine to amine reduction using sodium cyanoborohydride.

Reductive Amination (Borch Reaction)

Reductive amination is the conversion of a carbonyl into an amine through an intermediate imine.[3] The carbonyl is first treated with ammonia to promote imine formation by nucleophilic attack. The imine is then reduced to an amine by sodium cyanoborohydride. This reaction works on both aldehydes and ketones. The carbonyl can be treated with ammonia, a primary amine, or a secondary amine to produce, respectively, 1°, 2°, and 3° amines.[4]

Reductive amination using sodium cyanoborohydride.

Reductive Deoxygenation of Ketones

Aromatic ketones and aldehydes can be reductively deoxygenated using sodium cyanoborohydride.[5] This means that the carbonyl oxygen is being removed completely from the molecule. Deoxygenation using sodium cyanoborohydride is often done in the presence of trimethylsilyl chloride, or TMSCl.[5]

Reductive deoxygenation of a ketone using sodium cyanoborohydride.

Preparation

Sodium cyanoborohydride can be purchase from most chemical suppliers. It is most commonly synthesized by the following methods:

Preparation from Sodium Cyanide and Diborane

Sodium cyanoborohydride can be synthesized from sodium cyanide and diborane.[citation needed]

This method of preparation can be used for other compounds of the formula RBH3CN where R is an alkali metal, a quaternary ammonium radical, or a phosphonium radical.[citation needed] The final products are useful as hydrolysis stable reductants and as synthetic intermediates.[citation needed]

Preparation sodium cyanoborohydride from sodium cyanide and diborane.

Selectivity

Since sodium cyanoborohydride is a mild reducing agent, many functional groups remain inert in its presence. For example, sodium cyanoborohydride is incapable of reducing amides, ethers, lactones, nitriles, and epoxides.[6] Therefore, it can selectively reduce some functionalities in the presence of others.

Some examples of sodium cyanoborohydride include:

The selectivity of this reducing agent makes it an important tool in organic synthesis. It allows for specific modifications to be made to complex organic molecules.

See also

References

  1. ^ Sigma-Aldrich Co., Sodium cyanoborohydride. Retrieved on 2014-11-09.
  2. ^ a b c 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.
  3. ^ Richard F. Borch (1988). "Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine". Organic Syntheses; Collected Volumes, vol. 6, p. 499.
  4. ^ 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.
  5. ^ a b Box, Vernon G. S.; Meleties, Panayiotis C. (1998-09-24). "Reductive, selective deoxygenation of acylbenzo[b]furans, aromatic aldehydes and ketones with NaBH3CN-TMSCl". Tetrahedron Letters. 39 (39): 7059–7062. doi:10.1016/S0040-4039(98)01519-6. ISSN 0040-4039.
  6. ^ a b c LANE, Clinton F. (1975). "Sodium Cyanoborohydride - A Highly Selective Reducing Agent for Organic Functional Groups". Synthesis. 1975 (03): 135–146. doi:10.1055/s-1975-23685. ISSN 0039-7881.
  7. ^ Paul, Avishek; Shipman, Michael A.; Onabule, Dolapo Y.; Sproules, Stephen; Symes, Mark D. (2021-04-15). "Selective aldehyde reductions in neutral water catalysed by encapsulation in a supramolecular cage". Chemical Science. 12 (14): 5082–5090. doi:10.1039/D1SC00896J. ISSN 2041-6539. PMC 8179549. PMID 34163748.{{cite journal}}: CS1 maint: PMC format (link)
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