What is Sodium cyanoborohydride？

Description

Sodium cyanoborohydride is a chemical compound with the formula Na[BH₃(CN)]. It is a white powder, but commercial samples can appear tan. The salt tolerates aqueous conditions. There are many methods for synthesizing sodium cyanoborohydride, such as hydrocyanic acid and sodium borohydride as raw materials.

Uses

Sodium cyanoborohydride (NaBH₃CN) is a mild reducing agent that is commonly used in reductive aminations. Compared to sodium borohydride, the presence of electron-absorbing cyanide (CN) makes it less reactive[1]. This reduced reactivity allows NaBH3CN to be employed at neutral or slightly acidic conditions for the selective reduction of iminium ions in the presence of ketones and aldehydes. Since the reaction rate for the reduction of iminium ions is much faster than for ketones or even aldehydes, sodium cyanoborohydride can be carried out as a one-pot procedure by introducing the reducing agent into a mixture of the amine and carbonyl compound[2-3]. It can be used as a foaming agent for plastics, rubber and its adhesives, ethylene polymerization catalyst, color improver for paper and fiber, mercury-containing sewage treatment agent, hydrogenating agent for the preparation of dihydrostreptomycin, and as a raw material for the manufacture of potassium borohydride, borane, etc.

Toxicity

The presence of CN groups makes its toxicity problem not negligible. The reduction process of sodium cyanoborohydride produces highly poisonous hydrogen cyanide, which may render the final product toxic.  Gurram et al. tested a variety of reducing agents such as dimethylamine borane， triethylamine borane, trimethylamine borane, pyridine borane, morpholine borane, 2-picoline borane, and 5-ethyl-2-methyl-pyridine borane and found that pyridine borane could select as alternatives to sodium cyanoborohydride for the PEGylation of L-asparaginase[4]. Because it is hazardous to water, materials cannot be discharged into the surrounding environment without government permission.

References

[1] Elliger C, et al. Deoxygenation of Aldehydes and Ketones with Sodium Cyanoborohydride. Synthetic Communications , 1985; 15.

[2] Song J, et al. Synergistic Effect of Sodium Cyanoborohydride in Pb-Sn Perovskite Solar Cells. Advanced Functional Materials, 2023; 2304201.

[3] Gupton J, et al.  The Sodium Borohydride and Sodium Cyanoborohydride Reduction of Unsymmetrically Substituted 3-Chloro-2-propeniminium Salts. Synthetic Communications, 1986; 16: 1561-1574.

[4] Gurram S, et al. Pyridine Borane as Alternative Reducing Agent to Sodium Cyanoborohydride for the PEGylation of L-asparaginase. Applied Biochemistry and Biotechnology, 2021; 194: 827–847.