How is sodium borohydride similar to lithium aluminum hydride as a reducing agent? Could they be used interchangeably?

Question

How is sodium borohydride similar to lithium aluminum hydride as a reducing agent?  Could they be used interchangeably?

Wyatt Adkins · Accepted Answer

The molar mass of #NaBH_4# is #37.83*g*mol^-1#

Whereas the molar mass of #LiAlH_4# is #37.95*g*mol^-1#.

Equal masses of lithium and sodium salt would be needed because their molar masses are nearly equal. Each reagent would be expected to deliver at least three equivalents of hydride ions, depending on the quality of the hydride salt.

#"Moles of lithal"=(0.5*g)/(37.95*g*mol^-1)=??*mol#.

#"Moles of sodium borohydride"=(0.5*g)/(37.83*g*mol^-1)=??*mol#.

I always used lithal to deliver THREE equiv of hydride, and the workups of reaction based on 1/2 molar quantities were moderate. Note that lithal is a FAR more fierce reducing agent than sodium borohydride. Organic chemists often use lithal to DELIVER the one equiv of hydride...and water workup becomes pretty hairy.

Serenity Allen · Answer

undefined Sodium borohydride and lithium aluminum hydride are both commonly used as reducing agents in organic chemistry. They are similar in that they both donate hydride ions (H^-) to reduce various functional groups such as carbonyl compounds (aldehydes, ketones, and carboxylic acids) to their corresponding alcohols. However, lithium aluminum hydride is a stronger reducing agent compared to sodium borohydride and can reduce a wider range of functional groups, including esters and acid chlorides, to primary alcohols. Due to this difference in reactivity, they cannot always be used interchangeably, and the choice of reducing agent depends on the specific reaction requirements and desired outcome.