Alizarin-9-imine as indicator in acetonitrile and in pyridine media

The behaviour of alizarin-9-imine as an indicator in acetonitrile and pyridine media has been studied. The protonation constant in acetonitrile, K(I) = a(Hi) + a(H(+)) . a(I) = 10(-3.4), has been determined. Organic acids, amino-acids, and aliphatic and aromatic amines have been titrated with errors below 2%.