Porphins distribution

We have demonstrated recently that epoxidation and hydroxyl-ation can be achieved with simple iron-porphine catalysts with iodosylbenzene as the oxidant (24). Cyclohexene can be oxidized with iodosylbenzene in the presence of catalytic amounts of Fe(III)TPP-Cl to give cyclohexene oxide and cyclohexenol in 55% and 15% yields, respectively. Likewise, cyclohexane is converted to cyclohexanol under these conditions. Significantly, the alcohols were not oxidized rapidly to ketones under these conditions, a selectivity shared with the enzymic hydroxylations. The distribution of products observed here, particularly the preponderance of epoxide and the lack of ketones, is distinctly different from that observed in an autoxidation reaction or in typical reactions of reagents such as chromates or permanganates (15). 

Arguments over the tautomerization of porphine in crystals has not been resolved yet. The distribution of protons on the nitrogen atoms of porphine turned out to be disordered in an early X-ray study (Webb and Fleischer, 1965). A subsequent reinvestigation of the tautomerism of porphine by X-ray diffractometry, however, revealed that the protons are localized on nitrogen atoms as the trans form (Chen and Thlinsky, 1972 Tblinsky, 1973), while the... 

Porphyrins—Pigments widely distributed throughout nature (e.g., heme, bile pigments, cytochromes) consisting of four pyrroles joined in a ring (porphin) structure. 

Another important feature is transalkylation— the random rearrangement from etio or other alkyl porphins to a mixture of alkyl porphins based on a normal distribution pattern. Such a case has been tested in the laboratory e.g. vanadyl etio-porphyrin I pyrolyzed at 420 C will yield all other combinations of alkylporphins with substituents from one C to nine C as indicated by mass spectrometry (Figure 1.10). One such possibility is from structures VIII to IX in Figure 1.10. Transalkylation is analogous to Jacobson s rearrangement of aromatic hydrocarbons and occurs only under high temperature history. 

Porphyrins. Collective name derived from Greek porphyra=purple, purple snail, for the widely distributed purple (red) natural pigments formally prepared from the parent skeleton of porphine by substitution of the macrocylic tetrapyrrole framework with methyl, vinyl, acetic acid, propanoic acid units, or other substituents. 

In the protoporphyrins, the eight carbon atoms of porphin carry two vinyl groups, four methyl groups and two propionic acid groups. One of the fifteen possible isomers oif this structiure is protoporph3rrin IX or porphin-l 3 5 8-tetramethyl-2 4-divinyl-6 7-dipropionic acid, commonly called protoporphyrin. This is the porphyrin most widely distributed in nature, it is a constituent of haemoglobin, catalase, peroxidase, of cytochrome-6, etc. Diuing the course of putrefaction protoporphyrin loses its unsaturated side chains and is transformed into deuteroporphyrin III. On the other hand, it can be derived by a series of operations from copro-porphyrin III, another proof of its chemical kinship with the porphyrins of Series III. 

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