In situ photoproduction of dichlorodibenzo-p-dioxin from non-ionic triclosan isolated in solid argon |
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Authors: | Nihal Kuş Igor Reva Sevgi Bayarı Rui Fausto |
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Institution: | 1. Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal;2. Department of Physics, Anadolu University, 26470 Eski?ehir, Turkey;3. Hacettepe University, Faculty of Education, 06800 Ankara, Turkey |
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Abstract: | The infrared spectrum of triclosan or 5-chloro-2-(2,4-dichlorophenoxy)phenol] isolated in a low temperature (~15 K) argon matrix has been recorded and assigned with help of DFT claculations undertaken with the B3LYP functional and the 6-311++G(d,p) basis set. The obtained spectrum doubtlessly exhibits the characteristic vibrational signature of the neutral (phenol) form of the compound, which exists in two different conformations (forms I and II) in the matrix, in a I: II population ratio of ca. 0.75. Upon broadband UV irradiation of the matrix-isolated triclosan with unfiltered light provided by a xenon arc lamp, formation of 2,8-dichlorodibenzo-p-dioxin (2,8-DCDD) was observed, together with HCl. The reaction seems to occur through initial photoproduction of the triclosan phenol radical derivative, and involve in the initial step participation of dissociative (πσ1) excited states along the OH stretching coordinate, as observed previously for other phenol derivatives. The photochemically detached hydrogen atom derived from triclosan may then react with the closest located chlorine atom in the triclosan molecule to yield HCl and a biradical species, which can subsequently undergo a ring-closure reaction by intramolecular recombination, leading to the observed 2,8-DCDD. |
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