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Prophyrin complexes of nickel and other trace metals in petroleum are probably formed from chlorophyll which makes up a minor part of the organic matter from which petroleum develops. Since the chemical and physical environments for the formation of porphyrin complexes must be identical with those for the formation of crude oil, a knowledge of the conditions requisite for the formation of porphyrin complexes is important in defining the conditions under which the associated petroleum is formed. The present study was an investigation of one possible reaction in a likely sequence of reactions leading to the formation of petroleum porphyrins: the complexing of the immediate degradation product of chlorophyll, pheophytin, with nickel. Laboratory experiments were carried out t establish the rate and mechanism of the complexing reaction in the temperature range from 75 to 115°C. in methanol using nickel acetate and pheophytin a. It was clear that the reaction mechanism is ionic with the rate depending on the concentration of both nickel ions and pheophytin. The rate of reaction found for the complexing process is sufficiently rapid to indicate a ready formation of the nickel complex of pheophytin in recent sediments, given a reasonable supply of nickel in solution. It was apparent however that the complex is destroyed at sediment temperatures and this precludes the preservation of all but traces of it in recent sediments. It is concluded that the direct reaction between nickel and pheophytin probably does not play a significant part in the formation of ni kel porphyrin complexes in petroleum.
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