Question

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

Hint:

Converting a nitrile (R-C≡N) to an aldehyde (R-CHO) needs a partial (controlled) reduction that stops at the aldehyde stage and does not go all the way to an amine.

Answer 1

Step 1: Note what is needed.
We must change ethanenitrile \((CH_3-C\equiv N)\) into ethanal \((CH_3-CHO)\).

Step 2: Understand the difficulty.
The reduction must stop at the aldehyde stage and not go further to an amine, so a mild, selective reducing agent is needed.

Step 3: Recall the named reduction.
This controlled reduction of a nitrile to an aldehyde is the Stephen reduction.

Step 4: Name the reagent.
The reagent is stannous chloride and hydrochloric acid \((SnCl_2 / HCl)\), which forms an imine salt that is then hydrolysed to the aldehyde.

Step 5: Show the change.
\[CH_3-C\equiv N \xrightarrow{SnCl_2/HCl, \; then \; H_3O^+} CH_3-CHO\]

Answer: The reagent is stannous chloride with hydrochloric acid \((SnCl_2/HCl)\) followed by hydrolysis (Stephen reduction). Diisobutylaluminium hydride (DIBAL-H) is also acceptable.