Sodium cyanoborohydride
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| Names | |
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| IUPAC name
Sodium cyanoboranuide
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| Other names
Sodium cyanotrihydridoborate
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| Identifiers | |
3D model (JSmol)
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| ECHA InfoCard | 100.043.001 |
| EC Number |
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PubChemCID
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| UNII | |
CompTox Dashboard(EPA)
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| Properties | |
| Na[BH3(CN)] | |
| Molar mass | 62.84g·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 inmethanol insoluble indiethyl ether |
| Structure | |
| 4 at boron atom | |
| Tetrahedralatboronatom | |
| Hazards | |
| Occupational safety and health(OHS/OSH): | |
Main hazards
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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 |
| GHSlabelling: | |
  
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| Danger | |
| H228,H300,H310,H314,H330,H410 | |
| P210,P260,P264,P273,P280,P284 | |
| NFPA 704(fire diamond) | |
| 5 mg/m3 (TWA) | |
| Safety data sheet(SDS) | Sigma Aldrich[1] |
| Related compounds | |
Otheranions
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Sodium borohydride |
Related compounds
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Lithium aluminium hydride |
Except where otherwise noted, data are given for materials in theirstandard state(at 25 °C [77 °F], 100 kPa).
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Sodium cyanoborohydrideis achemical compoundwith the formulaNa[BH3(CN)].It is a colourless salt used inorganic synthesisforchemical reductionincluding that ofiminesandcarbonyls.Sodium cyanoborohydride is a milder reductant than other conventionalreducing agents.[2]
Structure[edit]
Sodium cyanoborohydride is a salt. Thecationicsodium ion, [Na]+,interacts with theanioniccyanoborohydride ion, [BH3(CN)]−.The anionic component of the salt istetrahedralat theboronatom.
Theelectron-withdrawingcyanidesubstituent 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 counterpartsodium borohydride,containing [BH4]−.[2]
Uses[edit]
Sodium cyanoborohydride is a mild reducing agent. It is generally used for the reduction ofimines.These reactions occur <pH 7 because the iminium ions are the actual substrates.[3]
Reductive amination,sometimes called theBorch reaction,is the conversion of acarbonylinto anaminethrough an intermediateimine.[4]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 withammonia,aprimary amine,or a secondary amine to produce, respectively, 1°, 2°, and 3° amines.[5]
Aromaticketonesand aldehydes can be reductivelydeoxygenatedusing sodium cyanoborohydride.[6]This means that the carbonyl oxygen is being removed completely from the molecule. Deoxygenation using sodium cyanoborohydride is often done in the presence oftrimethylsilyl chloride,or TMSCl.[6]
Preparation[edit]
Sodium cyanoborohydride can be purchase from most chemical suppliers. It can be synthesized by combiningsodium cyanideandborane tetrahydrofuran.[7]
- BH3·thf + NaCN → NaBH3CN + thf
Selectivity[edit]
Since sodium cyanoborohydride is a mild reducing agent, it gives goodchemoselectivityfor reaction with certainfunctional groupsin the presence of others. For example, sodium cyanoborohydride is generally incapable of reducingamides,ethers,estersandlactones,nitriles,orepoxides.[8]Therefore, it can selectively reduce some functionalities in the presence of others.
Some examples of selective reduction include:
- Reduction ofiminiumions in the presence ofcarbonyls[8]
- Reduction ofaldehydesin the presence ofketonesand esters.[9]
- Reduction of aldehydes in the presence ofthioesters[8]
The selectivity of this reducing agent makes it an important tool inorganic synthesis.It allows for specific modifications to be made to complex organic molecules.
History[edit]
Georg Wittigwas the first to synthesize a cyanoborohydride by treatinglithium borohydridewithhydrogen cyanidein 1951.[8]The corresponding compound, sodium cyanoborohydride, was synthesized following a similar rationale by reactingsodium borohydridewithhydrogen cyanide.[10]The synthesis was later refined to usesodium cyanideandboraneinTHFmaking the process safer.[10]
See also[edit]
- Sodium triacetoxyborohydride– a milder reductant, but unstable in water
- Sodium borohydride– a stronger, cheaper reductant
References[edit]
- ^Sigma-Aldrich Co.,Sodium cyanoborohydride.Retrieved on 2014-11-09.
- ^abcBaxter, 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.ISBN0-471-26418-0.
- ^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.ISBN978-0-470-84289-8.
- ^Richard F. Borch (1988)."Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine".Organic Syntheses;Collected Volumes,vol. 6, p. 499.
- ^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.
- ^abBox, 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.ISSN0040-4039.
- ^Hui, Benjamin C. (October 1980)."Synthesis and properties of borohydride derivatives".Inorganic Chemistry.19(10): 3185–3186.doi:10.1021/ic50212a075.ISSN0020-1669.
- ^abcdLANE, 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.ISSN0039-7881.S2CID95157786.
- ^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.ISSN2041-6539.PMC8179549.PMID34163748.
- ^abAbdel-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.ISBN978-0-8412-3381-2.
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