SYNTHESIS OF SOME NEW FUNCTIONALIZED 2,4,4,6-TETRAPHENYL-4H-THIOPYRANS AND STUDY ON THEIR PHOTOCOLOURATION

A series of nineteen new 2,4,4,6-tetraphenyl-4H-thiopyrans both symmet rically and asymmetrically functionalized in the 3- and 5-positions of the 4H-thiopyran ring (-Br, -NO2, -CN) and/or in the 4-positions of t he 2- and 6-phenyl groups (-Br, -CN, -OMe, -CO-Ph, -COCF3, -CO2H) was pre pared and the influence of the substituents on their photocolourat ion was followed. The title compounds were prepared by substitution re actions of the parent thiopyrans or by cyclization of suitably substit uted 1,3,3,5-tetraarylpentane-l,5-diones. The substances larking the 3 ,5-substituents exhibited blue or green UV-photocolouration while the 3- and/or 5-substituted species did not. Typical bleaching process for a selected compound is analyzed in terms of dispersive first-order ki netics.