Sodium Borohydride - A Versatile Reducing Agent

Introduction

The use of alkali metal borohydrides as reducing agents in organic chemistry is well documented since the pioneering work by H. C. Brown and colleagues. [1] After its first application in carbonyl reduction, [2] sodium borohydride has been widely used as an economical and mild reducing agent in the reduction of carbonyl and related compounds as well as other unsaturated compounds. [3] Suitable substrates [4] included conjugated carbonyl compounds, alkoxysulfonium salts, nitro compounds, carboxylic acids and esters, sulfonate esters, alkyl halides, nitriles, and amides. It was observed that the reducing activity was influenced by solvents and metal ions, [5] and can be finely adjusted by Lewis acid mediation. [6] Reduction in acidic media [7] was investigated extensively. Sodium borohydride (NaBH₄) is commercially available as a white crystalline powder with moderate hygroscopic property. It can be used as solution in lower alcohols, or in glymes for elevated temperature. In neutral and acidic water, NaBH₄ hydrolyzes to afford hydrogen gas, but a basic aqueous solution of NaBH₄ is stable and useful in the lab.

References

• 1 Schlesinger HI. Brown HC. Abraham B. Bond AC. Davison N. Finholt AE. Gilbreath JR. Hoekstra H. Horvitz L. Hyde EK. Katz JJ. Knight J. Lad RA. Mayfield DL. Rapp L. Ritter DM. Schwartz AM. Sheft I. Tuck LD. Walker AO. J. Am. Chem. Soc.  1953,  75:  186 
• 2 Chaikin SW. Brown WG. J. Am. Chem. Soc.  1949,  71:  122 
• 3a Oliveto EP. Hershberg EB. J. Am. Chem. Soc.  1953,  75:  488 
• 3b Brown HC. Rao BCS. J. Am. Chem. Soc.  1955,  77:  3164 
• 3c Kaplan LA. J. Am. Chem. Soc.  1964,  86:  740 
• 3d Crochet RA. Blanton CD. Synthesis  1974,  55 
• 4a Kadin SB. J. Org. Chem.  1966,  31:  620 
• 4b Johnson MR. Rickborn B. J. Org. Chem.  1970,  35:  1041 
• 4c Bhattacharjya A. Mukhopadhyay R. Pakrashi SC. Synthesis  1985,  886 
• 4d Ludley FH. Ralph J. J. Agric. Food Chem.  1996,  44:  2942 
• 5a Brown HC. Mead EJ. Rao BCS. J. Am. Chem. Soc.  1955,  77:  6209 
• 5b Santaniello E. Ferraboschi P. Sozzani P. J. Org. Chem.  1981,  46:  4584 
• 5c Suwinski J. Wagner P. Holt EM. Tetrahedron  1996,  52:  9541 
• 6a Brown HC. Rao BCS. J. Am. Chem. Soc.  1956,  78:  2582 
• 6b Kanth JVB. Periasamy M. J. Org. Chem.  1991,  56:  5964 
• 6c Liu C. Burnell DJ. Tetrahedron Lett.  1997,  38:  6573 
• 7a Gribble GW. Lord PD. Skotnicki J. Dietz SE. Eaton JT. Johnson JL. J. Am. Chem. Soc.  1974,  96:  7812 
• 7b Gribble GW. Nutaitis CF. Synthesis  1987,  709 
• 8a Corey EJ. Bakshi RK. Shibata S. J. Am. Chem. Soc.  1987,  109:  5551 
• 8b Jiang B. Feng Y. Zheng J. Tetrahedron Lett.  2000,  41:  10281 
• 8c Zhou Z. Tang Y. Wang L. Zhao G. Zhou Q. Tang C. Synthesis  2004,  217 
• 8d Schmitzer A. Perez E. Rico-Lattes I. Lattes A. Tetrahedron Lett.  1999,  40:  2947 
• 9a Tamami B. Mahdavi H. Tetrahedron  2003,  59:  821 
• 9b Baruah B. Dutta MP. Boruah A. Prajapati D. Sandhu JS. Synlett  1999,  409 
• 10 Berkes D. Kolarovic A. Povazanec F. Tetrahedron Lett.  2000,  41:  5257 
• 11a Renu BC. Samanta S. J. Org. Chem.  2003,  68:  7130 
• 11b Ranu BC. Samanta S. Tetrahedron  2003,  59:  7901 
• 12a Caddick S. Judd DB. Lewis AKde K. Reich MT. Williams MRV. Tetrahedron  2003,  59:  5417 
• 12b Chary KP. Ram SR. Iyengar DS. Synlett  2000,  683 
• 12c Cho BT. Kang SK. Synlett  2004,  1484 
• 12d Fringuelli F. Pizzo F. Vaccaro L. Synthesis  2000,  646 
• 13 Patra A. Batra S. Bhaduri AP. Synlett  2003,  1622 
• 14a Maltese M. J. Org. Chem.  2001,  66:  7615 
• 14b Babu KS. Raju BC. Srinivas PV. Rao JM. Tetrahedron Lett.  2003,  44:  2525