Thiocyanate-assisted demetallation of α,β,γ,δ-tetra(p-sulfophenyl)porphinatoindium(III) in aqueous media

✍ Scribed by Warren L. Reynolds; Daniel Gall; Peter Arndt

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: English
• Weight: 435 KB
• Volume: 14
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550140805

✦ Synopsis

The rate law for the demetallation of the title indium(II1)-porphin complex in aqueous acidic thiocyanate media at 3.00M ionic strength was found to be of the form

where [H4P2-] is the concentration of the diacid product formed, [InPIt is t b e total concentration of all forms of indium(II1)-porphin complex present, and a and b are clonstants. The constant a is a pseudo-third-order rate constant with the value (0.057 f 0.005)M-2 s-l and b has the value 0.704M-2 at 50.5"C. If the mechanism for demetallation involves ringpuckering with the attachment of two H+ ions, then l / b can be identified with the product KlKz for the stepwise dissociation of two protons from two ring pyrrolic nitrogen atoms of HpInP-. In the sulfonated tetraphenylporphin used for these studies the ring pyrrolic nitrogen atoms seem to be the most probable sites for protonation. If this identification is correct, the value of 1.42 f 0.13 found for the product KlKz shows the enormous effect that the presence of the In3+ center has on the ionization constants of these two protons. That the kinetic studies show saturation effects with respect to proton addition to InP3-may result from the fact that In3+ sits about 0.6 8, above the porphin ring.