Salt effects on reactivity of some Fe(II)-Azo complexes catalyzing disproportionation of hydrogen peroxide

Ali M. Shaker, Aida M. Awad, Mohamed Adam

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Salt effects on kinetics of oxidation and decomposition of novel low-spin Fe(II) complexes of azo amino acids with hydrogen peroxide have been investigated in aqueous medium. The ligands are derived from amino acids (DL-phenylalanine, DL-tryptophane, histidine, and alanine) and p-nitroso aromatic substituted amines (N,N-dimethyl-4-nitrosoaniline and N,N-diethyl-4-nitrosoaniline). Hydrophobic salts of alkali metal and tetraalkylammonium halides, e.g., KBr, tetrabutylammonium bromide (TBAB), tetraethylammonium bromide (TEAB), and tetramethylammonium bromide (TMAB) have been used. Dilute salt solutions exhibit little effects on the reactivities of oxidation and decomposition of the title compounds. This behaviour would be ascribed to a decrease in the activity coefficients of the reacting species in these solutions. Moreover, these effects support the reported pathway in these reactions occurring via the association of dicationic complexes and undissociated H2O2. On the other hand, higher salt concentration shows considerable effects on the reactivities. This behaviour is explained in terms of hydrophilicity of the complexes, ion pair formation, salting out, and substituent effects. Hyrophilic nature of the recent complexes enhances reactivity with increasing [KBr] due to salting out effects in the aqueous medium. Increasing [TBAB] retards reactivity via ion pair formation with the reactants. In the presence of R 4N+ ions, the reactivity increases with changing R in the following order; R = C 4H9 < C2H5 < CH3. The bulky R groups in the added tetraalkylammonium salts, exert medium steric hindrance against the approach of reactants.

Original languageEnglish
Pages (from-to)421-431
Number of pages11
JournalMonatshefte fur Chemie
Issue number4
StatePublished - Apr 2006
Externally publishedYes


  • Azo amino acids
  • Hydrogen peroxide
  • Iron(II)
  • Salt effects


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