Spectrophotometric Determination of Aminophenol Isomers Via Oxidative Coupling Reaction with 4-Aminoantipyrine

A spectrophotometric method has been developed for the determination of aminophenol isomers (o-aminophenol, m-aminophenol and p-aminophenol). The method is based on oxidative coupling reaction of these compounds with 4-aminoantipyrine (4-AAP) in the presence of cupper sulphate as oxidizing agent in alkaine medium forming a reddish brown colour. The products show maximum absorption at 440 nm, 480 nm and 445 nm for o-aminophenol, m-aminophenol and p-aminophenol respectively. The molar absorptivities are 8.632103 ,9.33103 and 9.1449103 l.mol-1.cm-1 for concentrations obeyed Beers law in the range 1-20, 1-24 and 1-7 g.ml-1 for the above compounds respectively. The average recovery was ranged between 98.38% and 101.01% with relative standard deviation < 1.6 for all the studied compounds. The 4-AAP products were formed in the ratio of 1:2 aminophenol isomers : 4-AAP. The stability constant of the products was 7.4 108, 3.27108 and 9.94107 l2.mol-2 for o-aminophenol, m-aminophenol and p-aminophenol products respectively indicating the good stability of these products.