Why does nabh4 not react with esters

It is impossible to address this in a single article and most of them are beyond the scope of most undergraduate programs. However, below is a summary chart for the carbonyl reductions to alcohols that you likely need to know:. Once you learn these, go the following practice problems for the reduction of carbonyl compounds to alcohols:.

Alcohols from Carbonyl Reductions — Practice Problems. Notify me of followup comments via e-mail. You can also subscribe without commenting. NaBH 4 , on the other hand, is not so reactive and can be used, for example, in a selective reduction of aldehydes and ketones in presence of an ester: Notice that LiALH 4 and NaBH 4 reduce aldehydes and ketones to primary and secondary alcohols respectively.

NaBH 4 Reduction of Aldehydes and Ketones — The Mechanism Sodium borohydride reduces aldehydes and ketones by a similar mechanism with some important differences that we need to mention. The Mechanism of LiAlH 4 Reduction of Esters The reduction of an ester to an alcohol requires two hydride additions to the carbonyl group and therefore an excess of LiAlH 4 is used: This is because the tetrahedral intermediate formed after the first hydride addition contains a leaving group which is kicked out re-forming the carbonyl group: The newly formed carbonyl group is an aldehyde and it is more reactive than the ester, thus is attacked one more time by LiAlH 4 : This, again, is very similar to what we saw in the Grignard reaction of esters.

Despite the low reactivity of the carboxylate ion, the hydride addition does occur: The negatively-charged oxygen is then converted into a leaving group by coordinating to aluminum.

The Stereochemistry of LiAlH 4 and NaBH 4 Reduction The reduction of unsymmetrical ketones with LiAlH4 or NaBH4 produces a pair of stereoisomers because the hydride ion can attack either face of the planar carbonyl group: If no other chiral center are present, the product is a racemic mixture of enantiomers. Alcohols from Catalytic Hydrogenation Another common method for preparing alcohols from aldehydes and ketones is the catalytic hydrogenation: Remember, catalytic hydrogenation was the method for reducing alkynes to alkenes or alkanes depending on the specific reagent.

A Summary for Alcohol Reducing Reagents In addition to LiAlH 4 and NaBH 4, there are hundreds of different hydrides reducing agents designed for specific scenarios and combination of functional groups in the molecule. I think chemistry. Featured on Meta. Now live: A fully responsive profile.

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Accept all cookies Customize settings. These cannot attack an electron rich carbon-carbon double bond, or be attacked by a pair of negative electrons from a pi orbital. Why can't NaBH4 reduce alkenes? Can LiAlH4 reduce ketone? However, the double or triple bonds in conjugation with the polar multiple bonds can be reduced. Can LiAlH4 reduce carboxylic acids? Conversion of carboxylic acids to alcohols using LiAlH4. Carboxylic acids can be converted to 1o alcohols using Lithium aluminum hydride LiAlH4.

Note that NaBH4 is not strong enough to convert carboxylic acids or esters to alcohols. Is LiAlH4 a nucleophile? Why does NaBH4 not reduce carboxylic acids? The carbonyl carbon of a carboxylic acid is even more electrophilic than the carbonyl carbon in an aldehyde or ketone.

For this reason, sodium borohydride does not reduce a carboxylic acid. A carboxylic acid can react with an alcohol, in the presence of a small amount of an acid, to form a carboxylic acid ester. Is LiAlH4 a nucleophile? Why does NaBH4 not reduce carboxylic acids? The carbonyl carbon of a carboxylic acid is even more electrophilic than the carbonyl carbon in an aldehyde or ketone. For this reason, sodium borohydride does not reduce a carboxylic acid. A carboxylic acid can react with an alcohol, in the presence of a small amount of an acid, to form a carboxylic acid ester.

Why NaBH4 Cannot reduce primary halides? In NaBH4, the negative charge is developed by the non metal, B, which is relatively stable. This slows down the reaction making the hydride a weaker nucleophile.

Why does LiAlH4 react violently with water? The H-, hydride ions can react violently with water to liberate hydrogen gas and the solution becomes alkaline, now containing LiOH and Al OH 3.

LiAlH4 can react with methanol in the same way as it reacts with water but less violently since the O-H bond in methanol is less polar. Can LiAlH4 reduce benzene?