Protonation constants of ethane and propane frame-substituted oligophosphonic and oligophosphonocarboxylic acids

Abstract

The protonation constants of two oligophosphonic acids (propane-1,1,2,3-tetraphosphonic acid and ethane-1,1,2-triphosphonic acid), five phosphonocarboxylic acids (ethane-1,2-diphosphono-1-carboxylic acid, propane-1,1-diphosphono-2,3-dicarboxylic acid, ethane-1,2-diphosphono-1,2-dicarboxylic acid, ethane-1-phosphono-1,2-dicarboxylic acid and propane-1-phosphono-1,2,3-tricarboxylic acid) and (for comparison) ethane-1,1,2-tricarboxylic acid were determined pH-metrically. It is concluded that the basicity of the unprotonated oligoposphonate anion increases with the geminal position and the number of phosphonate groups in the molecule. In the case of the phosphonocarboxylic acids, a probable assignment of the protonation constants to the functional groups is given.