Mannich reactions have been carried out with a variety of model alkylphenols and dimethylamine, methylamine, and diethylenetriamine to trace the origin of persistent coloured products occurring in related reactions with pentadeca(e)nylphenol and 4-tert-alkylphenols. It was found to be attributable to the presence of resorcinolic impurities.

The coloured products from the reaction of resorcinols with methylamine, dimethylamine and other alkylamines have been studied. Phenoxazinones, xantheines and other nitrogenous compounds are formed.