Sodium cyanoborohydride

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Sodium cyanoborohydride
Sodium cyanoborohydride
Identifiers
CAS number 25895-60-7 YesY
PubChem 20587905
EC number 247-317-2
Jmol-3D images Image 1
Properties
Molecular formula 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) decomp
Solubility in water 212 g/100 mL (29 °C)
Solubility soluble in diglyme, tetrahydrofuran, methanol
slightly soluble in methanol
insoluble in diethyl ether
Hazards
MSDS External MSDS
EU Index not listed
NFPA 704
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g., diesel fuel Health code 3: Short exposure could cause serious temporary or residual injury. E.g., chlorine gas Reactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g., phosphorus Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Related compounds
Other anions Sodium borohydride
Related compounds Lithium aluminium hydride
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

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.[1]

Use[edit]

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.[2] 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").[3] In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones.[1]

Structure and preparation[edit]

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.[4]

References[edit]

  1. ^ a b Robert O. Hutchins, MaryGail K. Hutchins, Matthew L. Crawley "Sodium Cyanoborohydride" Encyclopedia of Reagents for Organic Synthesis, 2007 John Wiley & Sons. doi:10.1002/047084289X.rs059.pub2
  2. ^ 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
  3. ^ Richard F. Borch (1988), "Reductive Amination with Sodium Cyanoborohydride: N,N-Dimethylcyclohexylamine", Org. Synth. ; Coll. Vol. 6: 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. 

See Also[edit]

Sodium triacetoxyborohydride - a milder reductant and a less toxic alternative, but highly unstable in water