Question

How many mmoles of hydride are theoretically available in 250 mg of NaBH4?

Answer 1

Generally a chemist uses one equivalent of sodium borohydride to reduce an aldehyde or ketone. However, theoretically only 0.25 equivalents are necessary. Borohydride donates a hydride to the carbonyl carbon, generating borane, which is a weaker reducing agent than borohydride. However, borane is a Lewis acid that can react with the alkoxide formed in the reduction. This gives a new borohydride, which can reduce a second molecule of the ketone. This process can continue until all of the hydrides are consumed from the boron center. theretically one NaBH4 can donets 4 hydrides.

Here the 250 mg of NaBH4 use if we calculate the mmoles of hydride

= mass of NaBH4 / mol. weight of NaBH4

= 250 / 37.83 = 6.6085 mmoles of hydride will available.