Question

(r)-2-butanol reacts with potassium dichromate (k2cro4) in aqueous sulfuric acid to give a (c4h8o). treatment of a with sodium borohydride in ethanol gives b, which as the same boiling point and refractive index as (r)-2-butanol. draw the structure of

b.

Answer 1

Potassium dichromate reacts with sulfuric acid to form chromic acid, H₂CrO₄ which is a very strong oxidizing agent. The secondary alcohol, (R)-2-butanol will be oxidized in the presence of chromic acid, but it can only be as oxidized as far as the ketone, which is the product shown, 2-butanone.

Sodium borohydride is a reducing agent that will reduce a ketone or aldehyde to an alcohol. When sodium borohydride reacts with 2-butanone, it reduces it to 2-butanol. However, the alcohol is no longer chiral as it was in the beginning since the sodium borohydride can add a hydride to either face of the carbonyl, which results in a racemic mixture of alcohols. This explains why the product has the same refractive index and boiling point as (R)-2-butanol, however, the product formed would no longer be optically active.