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Sodium cyanoborohydride

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Sodium cyanoborohydride
Line-bond structure of sodium cyanoborohydride
Names
IUPAC name Sodium cyanoboranuide
Other names Sodium cyanotrihydridoborate
Identifiers
CAS Number
3D model (JSmol)
ECHA InfoCard 100.043.001 Edit this at Wikidata
EC Number
  • 247-317-2
PubChem CID
UNII
CompTox Dashboard (EPA)
InChI
  • InChI=1S/CH3BN.Na/c2-1-3;/h2H3;/q-1;+1
SMILES
  • C#N.
Properties
Chemical formula Na[BH3(CN)]
Molar mass 62.84 g·mol
Appearance white powder, hygroscopic
Density 1.083 g/cm (25°C)
Melting point 242 °C (468 °F; 515 K) decomposes
Solubility in water 212 g/(100 mL) (29 °C)
Solubility soluble in water, ethanol, diglyme, tetrahydrofuran, methanol
slightly soluble in methanol
insoluble in diethyl ether
Structure
Coordination geometry 4 at boron atom
Molecular shape 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:
Pictograms GHS02: FlammableGHS05: CorrosiveGHS06: Toxic
Signal word Danger
Hazard statements H228, H300, H310, H314, H330, H410
Precautionary statements 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
Threshold limit value (TLV) 5 mg/m3 (TWA)
Safety data sheet (SDS) Sigma Aldrich
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 , 100 kPa). ☒N verify (what is  ?) Infobox references
Chemical compound

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.

Structure

Sodium cyanoborohydride is a salt. The cationic sodium ion, , interacts with the anionic cyanoborohydride ion, . 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. This electronic phenomenon causes sodium cyanoborohydride to have more mild reducing qualities than other reducing agents. For example, Na is less reducing than its counterpart sodium borohydride, containing .

Uses

Sodium cyanoborohydride is a mild reducing agent. It is generally used for the reduction of imines. These reactions occur <pH 7 because the iminium ions are the actual substrates.

Reductive amination, sometimes called the Borch reaction, is the conversion of a carbonyl into an amine through an intermediate imine. 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.

Aromatic ketones and aldehydes can be reductively deoxygenated using sodium cyanoborohydride. 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.

Preparation

Sodium cyanoborohydride can be purchased from most chemical suppliers. It can be synthesized by combining sodium cyanide and borane tetrahydrofuran.

BH3·thf + NaCN → NaBH3CN + thf

Selectivity

Since sodium cyanoborohydride is a mild reducing agent, it gives good chemoselectivity for reaction with certain functional groups in the presence of others. For example, sodium cyanoborohydride is generally incapable of reducing amides, ethers, esters and lactones, nitriles, or epoxides. Therefore, it can selectively reduce some functionalities in the presence of others.

Some examples of selective reduction 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.

History

Georg Wittig was the first to synthesize a cyanoborohydride by treating lithium borohydride with hydrogen cyanide in 1951. The corresponding compound, sodium cyanoborohydride, was synthesized following a similar rationale by reacting sodium borohydride with hydrogen cyanide. The synthesis was later refined to use sodium cyanide and borane in THF making the process safer.

See also

References

  1. Sigma-Aldrich Co., Sodium cyanoborohydride. Retrieved on 2014-11-09.
  2. ^ 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. Hutchins, Robert O.; Hutchins, Marygail K.; Crawley, Matthew L.; Mercado-Marin, Eduardo V.; Sarpong, Richmond (2016). "Sodium Cyanoborohydride". Encyclopedia of Reagents for Organic Synthesis. pp. 1–14. doi:10.1002/047084289X.rs059.pub3. ISBN 978-0-470-84289-8.
  4. Richard F. Borch (1988). "Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine". Organic Syntheses; Collected Volumes, vol. 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.
  6. ^ 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.
  7. Hui, Benjamin C. (October 1980). "Synthesis and properties of borohydride derivatives". Inorganic Chemistry. 19 (10): 3185–3186. doi:10.1021/ic50212a075. ISSN 0020-1669.
  8. ^ LANE, Clinton F. (1975). "Sodium Cyanoborohydride - A Highly Selective Reducing Agent for Organic Functional Groups". Synthesis. 1975 (3): 135–146. doi:10.1055/s-1975-23685. ISSN 0039-7881. S2CID 95157786.
  9. 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.
  10. ^ Abdel-Magid, Ahmed F., ed. (1996-08-13). Reductions in Organic Synthesis: Recent Advances and Practical Applications. ACS Symposium Series. Vol. 641. Washington, DC: American Chemical Society. doi:10.1021/bk-1996-0641.ch001. ISBN 978-0-8412-3381-2.
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