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Dissociation of imino proton(s) of a highly water-soluble metal-free phthalocyanine and determination of its pKa value in water

Hiroaki Isago

National Institute for Materials Science, 1-2-1, Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan

Corresponding author, tel: +81 (029)-859-2734, fax: +81 (029)-859-2701.

SPP full member in good standing.

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and

Harumi Fujita

National Institute for Materials Science, 1-2-1, Sengen, Tsukuba-shi, Ibaraki 305-0047, Japan

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https://doi.org/10.1142/S1088424613500235Cited by:5 (Source: Crossref)

Abstract

Dissociation of imino proton(s) in the cavity of the macrocycle of a highly water-soluble, metal-free phthalocyanine (H₂(H₄tsppc); where H₄tsppc denotes tetrakis{(2′,6′-dimethyl-4′-sulfonic acid)phenoxy}phthalocyaninate) in ethanolic and aqueous solutions has spectrophotometrically been investigated. The spectral changes associated with reaction with NaOH have been found to involve one-proton transfer process in aqueous media while two-protons process in ethanolic media. The acid-dissociation constant of the first imino proton in water (in the presence of Triton X-100) has been determined to be 12.5 ± 0.2 (as pKa) at 25 °C. The doubly deprotonated species in EtOH has been easily converted to its corresponding cobalt(II) derivative by thermal reaction with anhydrous CoCl₂.

Dedicated to Professor Özer Bekaroğlu on the occasion of his 80th birthday

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