Chemical studies on the red sweat of the Hippopotamus

Hippopotamus produces colorless sweat over its entire body. The color of the sweat turns red within a few minutes and then becomes brown during a few hours by producing polymers. We isolated the unstable red and orange pigments, called hipposudoric acid and norhipposudoric acid, respectively, responsible to the red coloration of the sweat. Syntheses of these pigments were performed using the Pschorr reaction for the formation of the fluorenone core and the oxidation in the last step producing the unstable diquinone as the key steps. The tautomeric structures of the common chromophore of these pigments in a protic solvent and in an aprotic solvent were also discussed.