It was reported before that incomplete oxidation may result in formation of colored side-products such as hydroquinone,
quinhydrone or even polymeric species (Alejandre et al., 1999).
Co-crystals represent a long known class of crystalline solids (
quinhydrone was first reported in the 1840s by Wohler), but they remain relatively unexplored by chemists.
Instead,
quinhydrone, a 1:1 addition compound of hydroquinone and quinone is isolated in high yields (70-90%).
The pH of mill waters at the beater, stuff box, and head box was determined electrometrically, using a
quinhydrone electrode.
