Chemisorption Role of Clay Surfaces in the Synthesis of Porphyrins from its Raw Materials via Room Temperature Reactions

J. Hassen and J. Silver

Abstract
In the formation of porphyrin, at least one step is acid-catalyzed. Cation-exchanged clay was found to be able to provide the acidity needed in the formation of porphodimethine (an intermediate step in the route of porphyrin formation), from the reaction of pyrrole and aldehyde in water. Five different aldehydes were reacted with pyrrole in water in the presence of montmorillonite MMT and kaolinite KLT clays saturated with Fe(III), Cu(II), Cd(II), Co(II), Zn(II), Ni(II), and Na(I) cations. The initial appearance of a pink color, which indicates the beginning of the porphyrin formation, depends on the acidity of the cation in the exchanged sites of the clay, also on the cation exchange capacity of the clay. The intermediate compound was found to be formed in the montmorillonite interlayer in addition to the surface, and oxidized to porphyrin when desorbed from the clay surface by chloroform. In the presence of kaolinite, the intermediate compound formed only on the surface. The results were monitored using visible absorption spectra, diffuse reflectance spectra, and X-ray diffraction.

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Keywords
porphyrin-clay systems, montmorillonite, kaolinite, pyrrole, aldehyde