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Steric and Inductive Effects on the Basicity of Porphyrins and on the Site of Protonation of Porphyrin Dianions. Radiolytic Reproduction of Porphyrins and Metalloporphyrins to Chlorins and Phlorins

DOI: 10.1039/ft9938900495

Source and publish data:

Journal of the Chemical Society - Faraday Transactions p. 495 - 502 (1993)

Update date:2022-08-04

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Authors:

Sutter, Thimothy P. G.Sutter, Thimothy P. G.

Rahimi, RahmatollahRahimi, Rahmatollah

Hambright, PeterHambright, Peter

Bommer, Jerry C.Bommer, Jerry C.

Kumar, ManmohanKumar, Manmohan

Neta, PedatsurNeta, Pedatsur

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Article abstract of DOI:10.1039/ft9938900495

A series of sulfonated, water-soluble, phenyl-substituted porphyrins has been prepared, containing halogen or alkyl groups in the ortho, di-ortho or para position.While the para-substituted compounds exhibited monomer-dimer behaviour, all the ortho and di-ortho substituted porphyrins were monomeric in aqueous solution at 0.1 mol dm-3 ionic strength.The proton basicities varied over a 105 range along the series, from the strongly basic tetra(4-methoxyphenyl) species to the weakly basic and less deformable sulfonated tetrakis(2,6-dichlorophenyl)porphyrin.Certain of these porphyrins and related metalloporphyrins were reduced by radiolytic methods in aqueous solutions.Pulse radiolysis studies provided the spectra fo the short-lived ?-radical anions and γ-radiolysis led to formation of stable chlorins and phlorins, the products of two-electron reduction and protonation at the β-pyrrole or at the meso postion, respectively.Whereas H2TPPS4 yields phlorin at all pH values, Zn(II)-, Al(III)-, In(III)- and Sn(IV)-TPPS4 form phlorins at high pH and by increased metal electronegativity. 2,6-Disubstitution at the phenyl rings diminishes the likehood of phlorin formation.These and other results indicate that electron withdrawal from the porphyrin ?-system enhances the ratio of phlorin/chlorin production.On the other hand, steric crowding around the meso position retards protonation at this site by preventing the geometric reorientation necessary for phlorin formation.

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Product name:tris(4-sulfonatophenyl)monophenylporphyrin

Cas No:36951-71-0

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