The amino group is a strong activator, orienting to ortho/para. However, in acid media it is protonated, transforming into a strong deactivator (ammonium salt) that orients to the meta position.
Protonation of the amino can be avoided by protecting it with ethanoyl chloride in pyridine.
Aniline nitration without amino protection
![amino group protection protección del grupo amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino01.png)
Nitration of aniline with protection of the amino group, using ethanoyl chloride
![amino group protection protección del grupo amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino02.png)
Amino protection can be done with ethanoic anhydride in pyridine, or with ethanoyl chloride in pyridine.
![amino group protection protección del grupo amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino03.png)
The final product is an amide, much less basic than the starting amine and less prone to protonation. The mechanism of the reaction is as follows:
Stage 1. Addition
![amino group protection protección del grupo amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino04.png)
Stage 2. Acid-base balance
![amino group protection protección del grupo amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino05.png)
Stage 3. Elimination
![protection-amino06 proteccion-amino06](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino06.png)
The amide formed is deprotected by acid or basic hydrolysis, leaving the aniline free.
![protection-amino proteccion-amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino07.png)
Deprotection mechanism in basic medium.
Step 1. Addition of the hydroxyl group to the amide
![protection-amino proteccion-amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino08.png)
Stage 2. Elimination
![protection-amino proteccion-amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino09.png)
Stage 3. Acid-base balance
![protection-amino proteccion-amino](/images/stories/organica-i/benceno/proteccion-amino/proteccion-amino10.png)