Meso tetrakis ortho-, meta-, and para-N-alkylpyridinioporphyrins: kinetics of copper(II) and zinc(II) incorporation and zinc porphyrin demetalation

The relative reactivities of the tetrakis(N-alkylpyridinium-X-yl)-porphyrins where X = 4 (alkyl = methyl, ethyl, n-propyl), X = 3 (methyl), and X = 2 (methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-octyl) were studied in aqueous solution. From the ionic strength dependence of the metalation rate constants, the effective charge of a particular cationic porphyrin was usually larger when copper(II) rather than zinc(II) was the reactant. The kinetics of ZnOH+ incorporation and the acid catalyzed removal of zinc from the porphyrins in 1.0 M HCl were also studied. In general, the more basic 4- (para-) and 3- (meta-) isomers were the most reactive, followed by the less basic 2-(ortho-) methyl to n-butyl derivatives, with the lipophilic ortho n-hexyl and n-octyl porphyrins the least reactive. Copyright (C) 2003 Society of Porphyrins & Phthalocyanines.