Abstract
In the present work, the first data on the catalytic activity of d-metal complexes of petroleum porphyrins obtained via two-stage re-metallization (acid demetallization with subsequent metalation) of high-purity petroleum vanadyl porphyrins are presented. During acid demetallization of petroleum vanadyl porphyrins, the highest yield (49%) and spectral purity of free petroporphyrin bases were achieved with concentrated sulfuric acid and a diluted solution of vanadyl porphyrins in chloroform. In the series of divalent cations of Mn, Fe, Co, Ni, Cu, and Zn, only the last four metals are complexed with demetallated petroporphyrins without significant changes in their component composition, whereas the interaction with Mn and Fe cations causes an evident structural transformation or even full degradation of petroporphyrin macrocycles, respectively. The composition and spectral purity of petroleum porphyrin-containing reactants and products were analyzed by FT-IR, UV-Vis, NMR, and MALDI-TOF mass spectroscopic methods. The obtained petroporphyrin-based d-metal complexes were assayed by the reaction of 2-mercaptoethanol oxidative dimerization, in which the copper porphyrins exhibited the highest catalytic activity.
Highlights
In living nature, porphyrins are found in prosthetic groups of proteins and enzymes responsible for the processes of aerobic oxidation, oxygen transport, and peroxide destruction [1,2,3]
To reveal the best reaction conditions for vanadyl porphyrin demetallation, four different experiments were carried out, two of which were adopted from the literature with minor modifications
In the first two experiments, 98% sulfuric acid was used as a demetallation agent, while the reactions were conducted at different temperatures. Since it was pre-established that concentrated sulfuric acid destroys solid petroleum vanadyl porphyrins, the latter were pre-dissolved in chloroform before exposure to the acid
Summary
Porphyrins are found in prosthetic groups of proteins and enzymes responsible for the processes of aerobic oxidation, oxygen transport, and peroxide destruction [1,2,3]. Despite the great importance of these reactions for chemical industry, synthetic porphyrins have not found significant practical application on an industrial scale. Synthetic phthalocyanines, as readily accessible and low-cost analogs of porphyrins, have received widespread application [1]. Besides synthetic and natural porphyrins, there is another class of these compounds whose applied potential has not yet been evaluated. This is the fossil porphyrins (or petroporphyrins) found in heavy oils with high vanadium content. The petroporphyrin content in this kind of fossil raw material can reach 0.1%, which makes the heavy oil a promising source for the production of petroporphyrins on the industrial scale
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