What is the Difference Between LiAlH4 and NaBH4?

The main differences between LiAlH4 and NaBH4 are their selectivity, reducing power, and reactivity. Here is a comparison of their properties and reactions:

1. Selectivity: LiAlH4 is non-selective, meaning it reduces both C=O and C=C bonds. In contrast, NaBH4 is chemoselective and only reduces C=O bonds, not C=C bonds. For selective reduction, NaBH4 is preferred over LiAlH4.
2. Reducing Power: LiAlH4 is a stronger reducing agent than NaBH4 because aluminum is less electronegative than boron, making the Al-H bond in LiAlH4 more polar. As a result, LiAlH4 can reduce a wider range of functional groups, including carboxylic acids and esters, while NaBH4 is only strong enough to reduce aldehydes and ketones.
3. Reactivity: LiAlH4 reacts violently with water and must be used in dry solvents such as anhydrous ether and THF. On the other hand, NaBH4 is less reactive and can be used in the presence of water without reacting violently.

In summary, LiAlH4 is a more powerful reducing agent that can reduce a wider range of functional groups, but it is less selective and requires dry conditions for use. NaBH4, on the other hand, is more selective and less reactive, making it suitable for reducing aldehydes and ketones in the presence of water.

Comparative Table: LiAlH4 vs NaBH4

Here is a table summarizing the differences between LiAlH4 and NaBH4:

Both LiAlH4 and NaBH4 are reducing agents, but LiAlH4 is a stronger reducing agent than NaBH4 due to the weaker Al-H bond in LiAlH4, which makes it a better hydride donor. While both compounds can reduce aldehydes and ketones to the corresponding alcohols, LiAlH4 can also reduce carboxylic acids, esters, and amides, which NaBH4 cannot.