Abstract
Intermolecular hydrogen bonds (HB) and proton transfer (PT) complexes between 1,2-dihydroxyanthraqunone (alizarin-AZ) and some aliphatic amines including propylamine (PA), triethylamine (TEA), and pyrrolidine (PR) have been investigated spectrophotometrically in methanol (MeOH) and acetonitrile (MeCN). The formation constants of the proton transfer reactions (K-PT) have been estimated utilizing the minimum-maximum absorbances method. It has been found that K-PT was lower in MeCN. On the other hand, K-PT was greater in MeOH. Job's method of continuous variations and molar ratio photometric titrations were used to identify the composition of the PT complexes formed. On the basis of the rapidity of the PT reaction, a simple and accurate spectrophotometric method for determination of AZ was proposed. Beer's law was obeyed in the concentration range (1.0.10(-5) to 1.0.10(-4)) mol.L-1 in methanol and (1.0.10(-5) to 2.0.10(-4)) mol.L-1 in acetonitrile with excellent correlation coefficients. The recovery percentages ranged from (99.87 to 100.80) %, with relative standard deviations (RSD) ranging from (0.91 to 1.75).