Animated Solution for Chemistry - Organic Chemistry: Which one of the following reactions will not form acetaldehyde?

A Reagent's Tale

Welcome to a fascinating journey through the world of organic reagents! In this problem, we are tasked with identifying which of the given chemical reactions fails to produce acetaldehyde (${\text{CH}}_3\text{CHO}$). To solve this, we must act as chemical detectives, analyzing the specific behavior of each reagent.

Let's evaluate the first reaction. We have ethene reacting with oxygen in the presence of palladium and copper catalysts:

This is the famous Wacker process, an industrial method used to convert alkenes directly into aldehydes or ketones. In this specific case, ethene is beautifully oxidized to acetaldehyde. So, option (a) successfully forms our target molecule.

Now, look at the second reaction. We have ethanol, a primary alcohol, reacting with Jones reagent (${\text{CrO}}_3$ in ${\text{H}}_2{\text{SO}}_4$):

Jones reagent is a very strong oxidizing agent. When it encounters a primary alcohol, it doesn't just stop at the aldehyde stage. Instead, it aggressively oxidizes the alcohol all the way to a carboxylic acid. Therefore, ethanol is converted into ethanoic acid (acetic acid), not acetaldehyde. This makes option (b) our prime suspect!

Let's quickly verify the remaining options to be absolutely sure.

In option (c), we have acetonitrile reacting with DIBAL-H followed by hydrolysis:

DIBAL-H is a selective reducing agent. It carefully reduces nitriles to imines, which upon hydrolysis yield aldehydes. Thus, this reaction successfully forms acetaldehyde.

Finally, in option (d), we pass the vapors of ethanol over heated copper at $573\text{ K}$:

This process is known as catalytic dehydrogenation. The heated copper acts as a mild oxidizing agent by removing hydrogen gas, converting the primary alcohol into an aldehyde. Once again, acetaldehyde is formed.

Conclusion: Out of all the given options, only the reaction with Jones reagent forms a carboxylic acid instead of acetaldehyde. Therefore, option (b) is the correct answer.