Question

Write the name of the reagent to convert Ethanenitrile to Ethanal.

Hint:

Stephen's reduction is the specific named reaction used to prepare aldehydes from nitriles in many exam syllabi.

Answer 1

To convert Ethanenitrile (acetonitrile, \( CH_3CN \)) to Ethanal (acetaldehyde, \( CH_3CHO \)), the reagent that is typically used is diborane (B₂H₆). This is a selective reducing agent that works by reducing the nitrile group (-CN) directly to an aldehyde group (-CHO).
The reaction occurs in the presence of a solvent, often tetrahydrofuran (THF), which stabilizes the reaction intermediate and provides an efficient environment for the reduction. The process is part of the hydroboration reduction of nitriles, where diborane adds hydrogen atoms across the nitrile group, resulting in the formation of an aldehyde.
In the presence of diborane, the nitrile (\( -CN \)) group undergoes a two-step reduction process: first, the nitrile group is reduced to an imine, and then further reduction occurs, forming the aldehyde. The reaction can be summarized as follows:
\[ \text{CH}_3\text{CN} + 2\text{H}_2\text{O} \xrightarrow{B_2H_6} \text{CH}_3\text{CHO} \] Diborane acts as the reducing agent by donating hydrogen atoms to the carbon and nitrogen atoms of the nitrile group. The process results in the conversion of the nitrile to the aldehyde, with no over-reduction occurring (i.e., the aldehyde is not reduced to a primary alcohol). This reaction is valuable in organic synthesis because it allows for the selective reduction of nitriles to aldehydes without over-reducing them to alcohols. Diborane is highly selective and does not reduce other functional groups like ketones or esters under mild conditions, making it an ideal reagent for this transformation.
Therefore, to convert Ethanenitrile to Ethanal, diborane (B₂H₆) is the appropriate reagent, and the process provides a straightforward and efficient method for the synthesis of aldehydes from nitriles.