Lichen purple: Orcein
Belorussian translation
Orcein is the name given to the purple dye from lichens. In the 20th century orcein was used as a food colouring and as a microscopical stain. Unlike other ancient dyes, the chemical structure was not appreciated until the 1960s.
More about that later. How is it formed from the lichen? Precursors in the lichens are esters, depsides or depsidones which are hydrolysed to orcinol by ammonia. Have a peek at some of the structures involved. In the presence of air, ammonia and orcinol react to give a series of compounds with a phenoxazone structure.
 
      Orcein contains a variety of phenazones: hydroxy-orceins, amino-orceins and amino-orceinimines. Have a look at the structures page. Our knowledge of these structures and reactions is due to the extraordinary work of one man, Hans Musso (1925-1988), who published around 25 papers on the subject between 1956 and 1965 while working at the Organisch-Chemischen Institut der Universität Göttingen.  Hans Musso

This is what the chemistry looks like
chemical structures ; lecanoric acid; orcinol; an orcein
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