This reaction was first studied in 1880 by Zdenko Hans Skraup (1850-1910), a Czech scientist born in Prague city of Czech Republic. His other works were in the fields of natural products like the structure of alkaloids, synthesis of iso-quinolines etc. Skraup’s synthesis is a chemical reaction used to synthesize quinolines by the condensation of glycerine and alanine in the presence of a strong acid (c.H2SO4) and an oxidizing agent like nitrobenzene. Other examples of oxidizing agents used are As2O5 (Arsenic acid). Initially when the reaction was done, As2O3 was used as an oxidizing agent and the reac-tion was known as violet reaction. In the present day world, in this reaction, Nitrobenzene is used not only as an oxidi z-ing agent but also as a solvent.
The reaction in its essence is stated below:
The mechanism of the reaction still remained elusive, however, there is a good reason to believe that it proceeds via the formation of acrolein as the intermediate. Acrolein is obtained by the dehydration of glycerol in the presence of c.H2SO4. The steps in the mechanism are described below:
Step 1: Formation of acrolein by the action of H2SO4 on glycerine. Dehydration of glycerine results in the loss of two molecules of water ultimately resulting in the formation of acrolein.
Step 2: Action of Acrolein on Aniline forming the addition product and intramolecular electrophilic addition followed by protonation, dehydration and oxidation.
Some of the major applications of this reaction are listed below:
(1). Skraup’s synthesis is used to produce the malarial drug 4,6-dimethylquinoline from p-toluidine and methyl-vinyl-ketone.
(2). Benzoquinoline can be synthesized from α-Naphthylamine
(3). 1,10-Phenanthroline can be synthesized from 8-Aminoquinoline.
(4). 1,5-Naphthylidine can be synthesized from 3-Aminopyridine.
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