Hydroxy- and Methoxybenzene Derivatives with Benzenediazonium Salts — Chemical Behavior and Tautomeric Problems

The azo-coupling reactions between 4-nitrobenzenediazonium tetrafluoroborate and a series of benzene derivatives bearing at least one electron-donating hydroxy or methoxy substituent have been studied. Depending on the nucleophile and its relative ratio with the diazonium salt, it was possible to obtain mono- and disubstituted products as well as a trisubstituted product for phloroglucinol.The reactions between 3,5-diaminoanisole or 3,5-diaminophenol derivatives and 2 equiv. of diazonium salt gave the monosubstituted product in the first case and a diadduct in the second case; X-ray diffraction analysis revealed a highly symmetric structure for the latter.The different behaviors of hydroxy- and methoxy- substituted compounds was particularly evident for phloroglucinol and 1,3,5-trimethoxybenzene and may be rationalized on the basis of the different electronic effects of the substituents.The propensities of the aromatic rings to undergo H/D Exchange reactions were investigated for a series of substrates, and a comparison of the results obtained provided new insights into this phenomenon and permitted a better explanation of the findings reported here; a new particular interaction competes with the formation of a proton–phloroglucinol σ complex.