Print version Print setup

Large Scale reduction of Ketone with sodium borohydride; Benzhydrol

SyntheticPage 539
DOI: 10.1039/SP539
Submitted Feb 16, 2012, published Mar 14, 2012
Ramesha Ramakrishna (ramesha63@hotmail.com)
A contribution from ramesha


			Reaction Scheme: Large Scale reduction of Ketone with sodium borohydride

Chemicals Used

Benzophenone, 98%
Methanol, commercial
Sodium borohydride , commercial 

Procedure

Methanol (900 mL), Benzophenone (182 g, 1 mole) is added to a 2 l, 3 necked flask carrying mechanical stirrer, addition flask. A solution of sodiumborohydride (10.0 g, 0.26 mol) in 25 ml of 0.5 M sodium hydroxide (500 mg NaOH in 25 ml water) was freshly prepared and charged to the addition flask. The temperature of methanolic solution of benzophenone is raised to about 35oC. Aqueous solution of sodiumborohydride added slowly over a period of 1 h. After complete addition, the temperature was raised to 55 oC and maintained for 30 min and further refluxed for 1h. At this point TLC shows almost complete conversion of benzophenone to benzhydrol (TLC comparison is very difficult by UV even 0.5% benzophenone looks like more than 5% because of high UV activity of benzophenone compared to benzhydrol). Methanol was completely removed by reduced pressure. To the, residue was added water (500mL)+ toluene (1000 mL, or other organic solvents) . The pH of the medium was adjusted to about 5-6 with dilute acetic acid (~ 5 mL). The organic layer was washed with water twice (250 mL x 2). Toluene was completely removed under reduced pressure to get 175 g of pure benzhydrol which solidifies on cooling (yield: 95%, repeated extraction of water will improve the yield further).

Author's Comments

1. Sodium borohydride is relatively stable in aqueous solution if the pH is above 10. Therefore it is possible to use all the hydrogen if the reaction medium is maintained alkaline.

2. Most literature procedure are done at either neutral or acidic conditions. Therefore more than 0.5 molar equivalent sodiumborohydride is used for the conversion. Because of this during workup there is large amount of hydrogen is liberated and it also poses safety risk.

3. For much larger scale, it is preferable to use nitrogen atmosphere during the reaction.

4. This is a practical method which can be used for any ketones/carbonyl compound

 

Data

1H NMR (300 MHz): 7.50-7.20 (m, 10H), 5.83 (s, 1H), 2.20 (s,OH)

13C NMR (75 MHz): 142.00, 128.25, 127.30, 127.12, 79.92

 


Lead Reference

Banfi, L.; Narisano, E.; Riva, R.; Stiasni, N.; Hiersemann, M. “Sodium Borohydride” in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York.doi:10.1002/047084289X.rs052.

This page has been viewed approximately 10299 times since records began.

Get structure file (.cdx, .sk2, .mol)

Keywords: alcohols, aromatics/arenes, benzhydrol, benzophenone, ketones, reduction, sodiumborohydride

Post new comment
Loading ...