2,3,5,6,8-Pentahydroxy-1,4-naphthalenedione, also called 2,3,5,6,8-pentahydroxy-1,4-naphthoquinone or spinochrome D, is an organic compound with formula C
5, formally derived from 1,4-naphthoquinone through the replacement of five hydrogen atoms by hydroxyl (OH) groups.
Spinochrome D occurs naturally as a brownish red pigment in the shell and spines of sea urchins such as the Japanese aka-uni (Pseudocentrotus depressus). It is soluble in diethyl ether and crystallizes as brownish red needles that sublime at 285−295 °C.
The compound gives a yellowish brown solution when treated with sodium hydroxide, a bluish green solution with ferric chloride, and a violet precipitate with lead acetate. It forms a five-fold acetate ester, C
3COO)5, that crystallizes from methanol as yellow needles that melt at 185−186 °C.