The reaction needs a protection step. Give full reaction, including protection and deprotection steps?

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1 Answer
Jun 1, 2018

Answer:

Here's what I get.

Explanation:

(a) Why do we need a protection step?

You are using potassium permanganate to oxidize an amine to a nitro group.

The problem is that the permanganate will also oxidize to aldehyde to a carboxylic acid.

You must first protect the aldehyde group, then do the oxidation, and then remove the protecting group to regenerate the aldehyde.

(b) The overall reaction

(i) Protection

A standard method of protecting an aldehyde group is to react it with
ethane-1,2-diol with p-toluenesulfonic acid in refluxing toluene.

The reaction is

Protection

The reaction is reversible, so you use a Dean-Stark apparatus to remove the water continuously as it forms.

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Dioxolanes are stable in basic solution, but they are sensitive to acid-catalyzed hydrolysis.

(b) Oxidation

Alkaline #"KMnO"_4# converts unsubstituted tertiary amines to nitro compounds.

Oxidation

(c) Deprotection

Treatment with aqueous acid hydrolyzes the dioxolane back to the aldehyde.

Deprotection