NaBH4 as the Reducing Agent

Illustrative examples of the reductive alkylation of support-bound amines are listed in Table 10.7. Further examples have been reported [134-138]. Closely related to the reduction of iminium salts is the reduction of A-alkylpyridinium salts, which has been successfully accomplished on Wang resin using NaBH4 as the reducing agent (DMF/ MeOH (1 1), 2 x 4 h Entry 11, Table 15.23 [139]). 

This is a reaction that would also work in the laboratory with NaBH4 as the reducing agent, but there is a big difference. The product from the NaBH4 reaction must be racemic-—no optical activity has been put in from compound, reagent, or solvent. 

Figure 7.7. Influence of the sonicatlon amplitude (A) and sonicatlon time (B) on the yield of Hg from Metig - (m) and PhHg ( ). Oxidation conditions 1 mol/l HCI, 5 ml sample and NaBH4 as the reducing agent, 3-min sonicatlon time in (A) and 60% amplitude in (B). (Reproduced with permission of the American Chemical Society, Ref [43].)...

Scheme 2.2 Synthesis of IL-modified Au NPs with NaBH4 as the reducing agent in a thiol-functionalized IL.

Braman et al. [713] suggested the use of sodium borohydride (NaBH4) as a reducing agent to replace the metallic zinc used in the classical Marsh test, which is awkward to handle and often contains large blanks of the elements of interest. Sodium borohydride is now used almost exclusively in the various modifications of the hydride method. 

Fig. 10 Transmission electron micrographs showing the control of the size of the gold nanoparticles synthesized using NaBH4 (0.02 M) as the reducing agent by altering the Wq. a Wo = 40, b Wo = 50, c Wo = 60, d Wo = 100...

A useful alternative to NaBH4 as a reducing agent, particularly when there are reactive carbonyl groups in the molecule, is NaCNEJHa, which still reduces BugSnHai but will not touch aldehydes or ketones. 

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