Oxidative Polymerization Studies of 8-Hydroxyquinoline in Different Media

Oxidative polymerization reaction of 8-hydroxyquinoline (HQ) in different media has been studied experimentally by spectrophotometric technique and confirmed computationally by molecular mechanics (MM+) calculations. MM+ calculations showed that the PE of the optimum molecular geometric (OMG) of the anionic HQ (HQ-NaOH) form is about two (1.985) times greater than the PE in the protonated (HQ-HCl) form. PE of the OMG structure of the PHQ was computed (-30.651 kJ mol-1). These calculations indicate that the matrix is highly stable. The oxidation constant (Kox) of the anionic form (HQ-NaOH) is about twice (2.02) greater than that of the protonated (HQ-H2SO4) form. The proposed procedure was success fully applied for the oxida tion of diiodohydroxyquinoline in streptoquin (SQ) (anti-di ar rhea, tab lets). The Kox of HQ in SQ was also found to be lower than the Kox in synthetic (HQ) solution. Kinetic parameters of the oxidative polymerization of the anionic form of HQ (HQ-NaOH) were deduced on the basis of absorbance variations. The results of computer-oriented kinetic analysis indicate that the rate-controlling step of the HQ polymerization is governed by Ginstling-Bronstein equation representing the three-dimensional diffusion (D4). Activation parameters of the oxidative polymerization of the anionic form of HQ (HQ-NaOH) were computed and discussed.