Spectrophotometric Study on the Complex Formation of Hydroperoxide with Tetraphenylporphyrin Cobalt(II)

Abstract

Abstract The rate constants, activation energies, activation entropies and equilibrium constants for the coordination of 1,2,3,4-tetrahydro-1-naphthyl hydroperoxide (THP), 1-methyl-1-phenylethyl hydroperoxide (CHP) and t-butyl hydroperoxide (BHP) to para-substituted tetraphenylporphyrin Co(II), Co(p-X)TPP (X=OCH3, H, Cl) were obtained by the visible spectral method at 235–245 K. The rate constants of coordination were k=0.097–2.03×102 M−1 s−1, the equilibrium constants being K=0.692–2.5×10−6 M−1. As a para-substituent effect on k and K, the constants were found to increase with increase in the electron donating property of the substituent group. They also depend on the kind of hydroperoxide, the rate constants decreasing in the order kTHP>kCHP>kBKP, and the equilibrium constants in the order KCHP>KBHP>KTHP. Activation energies were 7.0—7.8 kcal mol−1 and activation entropies −21–−25 cal K−1. No spectral change by the addition of hydroperoxide to CuTPP and NiTPP was observed.