The Mannich reaction has been used to prepare a number of amino derivatives of phenolic compounds whose physiological properties are being investigated. For this study certain mono-and dihydroxy compounds with two benzene rings, whether adjacent as in biphenyl or separated by some group X in the type formulas below, were selected as intermediates.
![4,4'-thiobis[2,5-xylenol] Structure](https://image.chemsrc.com/caspic/384/79718-64-2.png)