Question

In this experiment we reduced benzil to hydrobenzoin using NaBrH4 in ethanol. Name four other reducing agents that would work instead of NaBrH4 and list the disadvantages and advantages of each.

Answer 1

Other reducing agents that can be used are: Lithium aluminum hydride, lithium hydride, lithium borohydride and sodium hydride
Advantages and disadvantages
The decreasing order of reactivity is: Lithium aluminum hydride, lithium borohydride and sodium borohydride
Sodium borohydride due to its lower reactivity, allows its use in alcoholic and aqueous solutions in contrast to aluminum and lithium hydride. Sodium borohydride reacts with alcohols and water slowly, its reaction with carbonyl compounds is faster, so the use of protic solvents is feasible compared to lithium aluminum hydride and lithium borohydride.
Sodium hydride, lithium aluminum hydride has extreme reactivity to water. Lithium aluminum hydride is soluble in ether and insoluble in methanol and ethanol unlike sodium borohydride.
Lithium aluminum hydride is a reducing agent that reacts not only with aldehydes and ketones but also with many carbonyl compounds such as carboxylic acids, anhydrides, amides and esters. And it reduces other non-carbonyl groups such as alkyl halides, alkylazides and nitriles.
Lithium aluminum hydride easily reduces other groups such as: carboxylic acids, epoxides, lactones, nitro groups, nitriles, azides, amides and acid chlorides, in contrast to sodium borohydride which has an inert behavior.