DEACETALIZATION BY PHOTOINDUCED ELECTRON-TRANSFER WITH A PYRYLIUM SALT - EFFECT OF LIMITING THE AMOUNTS OF WATER, OXYGEN AND SENSITIZER

The photodeacetalization of 4-(p-isopropylphenyl)-2-nonyl-1,3-dioxolan e 1 using 2,4,6-triphenylpyrylium tetrafluoroborate (TPT) as sensitize r has been studied to explore the possibility of achieving a slow sunl ight-controlled release of polymer-bound carbonyl functionalized semio chemicals. This reaction has been found to produce mainly n-decanal an d p-isopropylbenzaldehyde, together with lower amounts of the correspo nding acids. The degree of conversion and the product distribution dep ended on the presence of water or oxygen and the amount of photosensit izer. The results are justified through generation of the radical cati on 1(+.), followed by ring opening and trapping of the radical/cationi c sites by oxygen or water. The delocalized 1,3-mdical cations III and the ozonides IV appear to be involved as key intermediates. Formation of n-nonanal as a minor product is explained through cleavage of the C-2-nonyl bond of 1(+.).