REACTIONS OF SULFUR(IV) WITH (TETRAETHYLENEPENTAMINE)IRON(III)

The reactions of S(IV) with Fe(III) in the presence of tetraethylenepe ntamine(T) have been investigated at pH = + 3.6-4.2 Fe(III) is bound b y the amine in a tridentate fashion (Fe(TH2)(5+)) with the two termina l primary amino groups remaining in the protonated form. The species F e(TH2)(5+) undergoes sulphite substitution to yield Fe(TH2)(SO3)(3+). The rate and activation parameters for the formation and dissociation of the sulphito complex are reported. Reduction of Fe(III) by the coor dinated sulphite is slow. The redox reaction reveals the existence of two isomers of Fe(TH2)(SO3)(3+) in which SO32- is bonded trans-or cis to the coordinated H2O (axial or equatorial). From the reactivity tren d it is presumed that the coordinated sulphite in the trans isomer red uces Fe(III) centre faster (by a factor of similar to 10) than the sam e in the cis isomer. The product distribution experiments show that SO 3- dimerises to S2O62- besides being oxidised to SO42- by Fe(III).