Chemistry and photochemistry of 2,6-bis(2-hydroxybenzilidene)cyclohexanone. An example of a compound following the anthocyanins network of chemical reactions

J Phys Chem A. 2014 Aug 14;118(32):6208-15. doi: 10.1021/jp505533b. Epub 2014 Aug 4.

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)cyclohexanone exhibits a slow color change from yellow to red styrylflavylium under extreme acidic conditions. The rate constant for this process (5 × 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 (1)H 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-d]xanthene by cyclization in solutions of acid to neutral range.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anthocyanins / chemistry*
  • Benzyl Compounds / chemistry*
  • Cyclohexanones / chemistry*
  • Hydrogen-Ion Concentration
  • Models, Molecular
  • Molecular Structure
  • Photochemical Processes

Substances

  • 2,6-bis(2-hydroxybenzilidene)cyclohexanone
  • Anthocyanins
  • Benzyl Compounds
  • Cyclohexanones