Spectrophotometric Determination of Some Phenolic Compounds Via Oxidative Coupling Reaction Using 4-Aminoantipyrine

Abstract

A spectrophotometric method has been developed for the determination of some phenolic compounds (Catechol, Resorcinol and Quinol). 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 brown colour. The products show maximum absorption at 404 nm, 474 nm and 392 nm for Catechol, Resorcinol and Quinol respectively. The molar absorptivities are 12133, 7695 and 16570 l/mol.cm for concentrations obeyed Beer’s law in the range 0.2 - 14, 0.04 - 18 and 0.2 - 4 μg.ml-1 for the above compounds respectively. The average recovery was ranged between 97.72% and 100.05% with relative standard deviation less than 3.4 for all the studied compounds, The 4-AAP products were formed in the ratio of 1:2 phenolic compound: 4-AAP With the exception of the complex catechol:4-amino antipyrine, it is in a 1:1 ratio. The stability constant of the products was 1.8369 × 104 (l.mol-1) , 2.82 × 1010 and 1.285 × 1010 (l2.mol-2) for Catechol, Resorcinol and Quinol products respectively indicating the good stability of these products, The effect of a number of interfering substances represented by primary and secondary aliphatic alcohols, aliphatic amines and other organic compounds was also studied. Finally, the results obtained indicate the selectivity of the method as there was no interference from the additives.