Porphine (also called porphin) is a planar aromatic heterocyclic compound with a 12-carbon outside ring and four embedded pyrrole rings. It is a dark red crystalline solid that is soluble in some polar solvents such as pyridine and dioxane. It can be heated to 360 ºC without melting. Porphine is the parent compound of a family of biologically and chemically relevant compounds called porphyrins. The potential of these compounds is enormous and it would be advantageous to use the porphine (porphyrin) unit as a building block for the synthesis of diverse porphyrin complexes with a wide range of applications.
Porphine was first prepared by German chemists Hans Fischer and Wilhelm Gleim in 1935. It is the parent structure of a large family of natural compounds called porphyrins, many of which are essential to life. Fischer was a 1930 Nobel Prize winner for his research on two porphyrins, heme (a constituent of hemoglobin) and chlorophyll. These porphyrins, like many others, contain a metal atom coordinated to the four nitrogen atoms.
Porphine is the simplest porphyrin and represents the core macrocycle of naturally occurring and synthetic porphyrins. Low yields and expense, however, make the synthesis of porphine on a large scale impractical. Another challenge synthetic chemist's faced was the high insolubility of porphine. The apolar tetrapyrrolic ring structure of porphine means it is poorly soluble in most organic solvents and hardly water soluble. As a result of this almost all current chemical studies with porphyrins use the better soluble meso tetrasubstituted 2 or β-octasubstituted porphyrins.
Porphine (Porphyrin), the parent of porphyrins, plays an important role within the organism[1].
ChEBI: Porphyrin is a member of porphyrins and a tetrapyrrole fundamental parent. It has a role as a metabolite.
One of the most common and efficient methods for synthesizing porphyrins is the Lindsay process (an improved version of the Adler-Longo process). This method is used to synthesize meso-substituted porphyrins, such as tetraphenylporphyrin. Its core steps are as follows: First, under acid catalysts (e.g., trifluoroacetic acid (TFA) or p-toluenesulfonic acid (p-TsOH)) and high dilution conditions, pyrrole condenses with an aldehyde (e.g., benzaldehyde) to generate a porphyrinogen intermediate. Subsequently, an oxidizing agent (e.g., DDQ or chloroquinone) is added to the same reaction system to oxidize and aromatize the porphyrinogen into a stable porphyrin ring. The Lindsay process significantly improves the yield and purity of porphyrins by separating the condensation and oxidation steps and precisely controlling the reaction concentrations.
[1] Mathias O. Senge, et al. Porphyrin (porphine) — A neglected parent compound with potential. Journal of Porphyrins and Phthalocyanines. Vol. 14, No. 07, pp. 557-567 (2010).
