Chemistry and Photochemistry of 2,6-Bis(2-hydroxybenzilidene)cyclohexanone

A. J. Moro, Ana-Maria Pana, Liliana Cseh, Otilia Costisor, António Jorge Dias Parola, L. Cunha-Silva, Rakesh Puttreddy, Kari Rissanen, Fernando Jorge da Silva Pina

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

The kinetics and thermodynamics of the 2,6-bis(2-hydroxybenzilidene)cyclohexanone chemical reactions network was studied at different pH values using NMR, UV-vis, continuous irradiation, and flash photolysis. The chemical behavior of the system partially resembles anthocyanins and their analogue compounds. 2,6-Bis(2-hydroxybenzilidene)cydohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 x 10(-5) s(-1)) is pH independent and controlled by the cis-trans isomerization barrier. However, the interesting feature is the appearance of the colorless compound, 7,8-dihydro-6H-chromeno[3,2-d]xanthene, isolated from solutions of acid to neutral range, characterized by H-1 NMR and single crystal X-ray diffraction. Light absorption by 2,6-bis(2-hydroxybenzilidene)cyclohexanone solutions immediately after preparation exclusively results in cis-isomer as photoproduct, which via hemiketal formation yields (i) red styrylflavylium by dehydration under extremely acidic solutions (pH < 1) and (ii) colorless 7,8-dihydro-6H-chromeno[3,2-4canthene by cyclization in solutions of acid to neutral range.
Original languageEnglish
Pages (from-to)6208-6215
JournalJournal of Physical Chemistry A
Volume118
Issue number32
DOIs
Publication statusPublished - Aug 2014

Keywords

  • FLAVYLIUM ION
  • ISOMERIZATION
  • HYDRATION

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