Ion-pair formation as a determining factor in the effectiveness of the interaction of electrolytes with amphiphilic azo dyes in water

Abstract

The order of effectiveness of added simple electrolytes (BaCl₂, CaCl₂, SrCl₂, LiCl, NaCl, KCl, RbCl and CsCl) in influencing the spectrum of four amphiphile azo-dye sulphonates (Methyl Orange and its homologues) has been determined spectrophotometrically.

The order found for Benzyl Orange corresponds to that for Methyl Orange but differs from those for Ethyl Orange and Orange IV. As with Benzyl Orange, the order of effectiveness does not correspond to either a lyotropic series or a ‘salting-out power’ series but can be related to the previously reported association constants for azo-dye anions and added cations.

This correlation confirms the importance of competitive hydration and ion-pair formation as intermediate steps in processes involving electrolytes and amphiphilic molecules in water.