Pauly reaction

The Pauly reaction is used for the qualitative detection of the amino acids tyrosine and histidine. It is named after its discoverer Hermann Pauly ( 1870-1950 ).

Reaction

Tyrosine and histidine have an aromatic ring, can easily be made on the electrophilic substitutions. Diazotized sulfanilic acid couples with the aromatic ring to form a red azo dye

In the first step, the diazotization is carried out by addition of sulfanilic acid sodium nitrite in the presence of hydrochloric acid. After the addition to the amino acid solution is made alkaline and in the presence of aromatic groups, the formation of the azo dyes, eg Azotyrosin done.