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ISSN 1998-9539

Reactivity of Porphyrazines in Acid-Base Interaction with N-Bases

Oleg A. Petrov,@ Galina V. Osipova, and Olga G. Khelevina


Ivanovo State University of Chemistry and Technology, Ivanovo, 153000, Russia


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The analysis of porphyrazine reactivity in the processes of acid-base interaction with proton acceptor molecules, containing nitrogen atom, in benzene solutions is carried out. It is shown that tetrahalogenoporphyrazines are evident as dibasic NH-acid in relation to organic bases such as pyridine, 2-methylpyridine, morpholine, benzylamine, n-butylamine, tert-butylamine, tri-n-butylamine, diethylamine, triethylamine or piperidine and form H-complexes with proton transfer, which are subjected to the kinetic process of destruction. In contrast, substituted phthalocyanines in system benzene (DMSO) - morpholine (benzylamine) form kinetically stable complexes with proton transfer. It is found that intermolecular transfer of NH-group protons from porphyrazine macrocycle to the organic base is a remarkably slow process (k298 = 10-2 - 10-6 l⋅s-n⋅mol-n) and is described by the total kinetic equation of the second or third order. The correlation dependence for tetrahalogenoporphyrazines between the reaction rate and pKa value of nitrogen containing bases is revealed. It is found that spatial screening of proton-acceptor centre prevents a favorable contact of acidbase centers of interacting molecules and obstructs the proton transfer from the acid to the base. It is shown that modification of porphyrin macrocycle owing to tetraazasubstitution and benzoannulation effects on the acid properties of the molecule. When passing from tetrahalogenoporphyrazines to substituted phthalocyanines the rate of the proton transfer decreases by several orders of magnitude on the background of growing Ea and ΔS characteristics. When changing benzene for DMSO the proton drawing from the macrocyclic plane is facilitated under action of the base.

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