A mechanistic study of the synthesis of meso‐tetraphenylporphin

Abstract

In continuation of an earlier preliminary study, some further physical and synthetic studies on the homogenous phase condensation of pyrrole and benzaldehyde to ms‐tetraphenylporphin in acidic media were undertaken. The role of atmospheric oxygen in the reaction was studied in some detail. The effects of acidity, solvent, concentration, and other constraints on both the rate and yield of the reaction were also investigated. Details of the mechanism, including possible intermediate structures, have been clarified and a reaction scheme accounting for the data is presented.

Synthesis and Stereochemistry of Hydroporphyrins

“…Chlorins are usually found as the undesired by-products in weso-tetraarylporphyrins, 7,8 and a wide variety of chlorins is accessible by suitable modification of chlorophylls. 9~12a The recent progress in the chemical modification of chlorophyll derivatives is summarized in the appendix to this chapter.…”

“…7,8 These are usually undesired contaminants of the porphyrins, and methods have been devised for their removal by selective oxidation to porphyrins. 33 If the chlorins are the desired products, they can be separated by fractionated crystallization (which leaves the chlorins enriched in the mother liquor), by fractionated acid extraction (in which the lower basicity 34 of the chlorins is used 9,19 ), and, only with difficulty and only if small amounts have to be separated, by chromatography.…”

“…The mechanism of hydroporphyrin formation during the synthesis of TPP has been studied by several groups. 7,8,35,36 It could be shown that the initially formed TPP-porphinogen is oxidized in an acid-catalyzed reaction to the porphyrin via a porphodimethene 37 intermediate. 8 The chlorin is then formed by the subsequent re-reduction of the porphyrin.…”

“…(b) Porphyrins (1) are reduced subsequently to phlorins (5) and porphomethenes (10). (c) The reduction of chlorins yields the corresponding structures with one peripheral double bond removed, namely, chlorinphlorins (9) are obtained from chlorins (4), and metallochlorinporphodimethenes (11) are obtained from metallochlorins (7). Structures of chlorin reduction products beyond the dihydrochlorin level are yet to be characterized, (d) Phlorins (5) can isomerize to chlorins (4)(see Section II, B), or they can be metalated to metalloporphodimethenes (6).…”

A new one pot and solvent-free synthesis of nickel porphyrin complex

“…Traditionally, porphyrin synthesis have been carried out in corrosive, high boiling solvents such as propionic acid (12,13) or in large amount of halogenated solvents containing a corrosive lewis acid catalyst (14Á16). In many cases, toxic oxidizing compounds are used to convert the porphyrinogen to porphyrin (17).…”