The reagent diisobutylaluminum hydride (DIBALH) reduces esters to aldehydes. When nitriles are treated with DIBALH followed by mild acid hydrolysis, the product is also an aldehyde. Propose a mechanism for this reduction.

The mechanism for both of these reactions is very similar to the mechanism for the reduction of acyl chlorides by LATB—H. The first step is an acid‐base reaction between an unshared electron pair on oxygen or nitrogen with the aluminum atom of the DIBAL—H. The second step is the transfer of a hydride ion from the DIBAL—H to the carbon atom of the carbonyl or nitrile group. The last step is the hydrolysis of the aluminum complex to form the aldehyde

Explanation:

Ozonolysis of alkenes

Alkenes in which the carbon(s) of the double bond possess one or more hydrogen atoms react with ozone (O 3) to generate aldehydes. The reaction of propene with ozone to form acetaldehyde and formaldehyde illustrates this method of preparation.

Hydroboration of terminal alkynes

Terminal alkynes react rapidly with borane to produce an intermediate compound that is easily oxidized to an aldehyde. For example, you can produce pentenal by reacting pentyne with borane and oxidizing the resulting intermediate with aqueous hydrogen peroxide.

Reduction of Nitriles To aldehydes:

The Nitriles can be reduced to aldehydes by Aluminum hydride (AlH).

DIBAL-H (diisobutylaluminum hydride) is generally used for the reduction of Nitriles.

Explanation:

Nitriles can also be reduced to aldehydes.

Reducing agent Diisobutylaluminium hydride, or DIBAL-H, is another commonly used metal hydride. DIBAL-H acts as a proton source, adding a hydride ion to the carbon of the nitrile. The resulting imine is a relatively stable intermediate that can be hydrolyzed to the aldehyde.

DIBAL-H is added in controlled amounts at low temperatures to achieve partial reduction of the nitrile. The aluminum atom in DIBAL acts as a Lewis acid, accepting an electron pair from the nitrile. The nitrile is then reduced by the transfer of a hydride ion to the carbon of the carbon-nitrile triple bond, producing an imine. After a workup with water, the aluminum complex is hydrolyzed to produce the desired aldehyde. Because the hydrolytic workup generates the aldehyde at the end, the nitrile does not undergo over-reduction.