pH-metric titration to characterize aci-nitro tautomerism

Purpose Organic molecules used as building blocks in drug discovery may have more than one tautomeric form. An example is 4-amino-2,6-dimethylphenylsulfonyl nitromethane (4-ADN) , an acidic molecule that exhibits aci-nitro tautomerism. In this work we used potentiometric titration to measure the pKa of this molecule, with the goal of forming tautomers and assessing their relative concentrations after exposure to acidic and basic conditions. A tendency to tautomerise might be considered a drawback in a molecular building block.