Acetyl chloride with arylamines

Direct nitration of aniline and other arylamines fails because oxidation leads to the formation of dark colored tars As a solution to this problem it is standaid practice to first protect the ammo group by acylation with either acetyl chloride or acetic anhydride... 

Any of the customary reducing agents suitable for converting aryl nitro groups to arylamines (Fe, HC1 Sn, HC1 H2, Ni) may be used. Acetylation of p-aminophenol may be carried out with acetyl chloride or acetic anhydride. The amino group of p-aminophenol is more nucleophilic than the hydroxyl group and is acetylated preferentially. 

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