1. Field of the Invention
The instant invention is a continuous method for oxidizing a substrate which is oxidizable by singlet oxygen. The method involves the steps of establishing a flow to and from each of a plurality of successive closed zones by charging the substrate in the liquid phase to the first zone, removing reaction product from the last zone, and transferring reaction product from the first zone and from each intermediate zone to the next succeeding zone. Each zone contains a quantity of a polymer-bound photosensitizing catalyst that is a source for singlet oxygen when irradiated by light of a particular wavelength, and is of such size and shape that a major portion of the catalyst therein can be made a source for singlet oxygen by irradiation with light of a suitable wavelength. Oxygen is introduced into each of the zones, and each is irradiated with light of a wavelength which causes the catalyst to be a source for singlet oxygen.
2. The Prior Art
Polymer-bound photosensitizing catalysts that are a source for singlet oxygen when irradiated by light of a particular wavelength are known, being disclosed, for example, by U.S. Pat. No. 4,315,998 granted to Neckers et al. on Feb. 16, 1982. The patent discloses, by way of illustration, the production of a polymer-bound photosensitizing catalysts from cross-linked polystyrene and chloromethylatedstyrene-divinylbenzene copolymer beads by reaction with acridine orange, chlorophyllin, crystal violet, Eosin Y, fluorescein, flavin mononucleotide, hematoporphyrin, hemin, malachite green, methylene blue, rhodamine B and rose bengal. The patent also discloses the production of polymer-bound photosensitizing catalysts where the polymer is a poly(2-hydroxyethyl)methacrylate 5 percent ethylene glycol polymer, a poly(2-hydroxyethyl)methacrylate 60 percent ethylene glycol polymer, a polyvinyl formal, a bromomethylated borosilicate glass, a styrenemaleic anhydride copolymer, and a polymer produced by reaction between sebacoyl chloride and hexamethylene diamine.
The Neckers et al. patent also discloses the use of the polymer-bound photosensitizing catalysts, for example, for the oxidation of 1,2-diphenyl-p-dioxene, 1,3-cyclohexadiene, tetramethylethylene, 1,2-dimethylcyclohexene and dihydropyran. The patent describes in detail only two procedures which involve the photooxidation of a substrate using a polymer-bound photosensitizing catalyst. One of these procedures, described in Example 22, involved the photooxidation of 140 milligrams of 1,2-diphenyl-p-dioxene and a six hour reaction, while the other, described in Example 31, involved the photooxidation of 97 milligrams of 2,3-diphenyl-p-dioxene and a 2-4 hour reaction time. Other photooxidation procedures described in the patent incorporate by reference the technique of Example 22. It will be appreciated that the photooxidation procedures described in the Neckers et al. patent are time-consuming batch processes where minute quantities of a substrate and of a polymer bound catalyst are charged to a single vessel and irradiated in the presence of oxygen to produce minute quantities of the oxidation products, and that the syntheses cannot be scaled up by charging larger quantities of the oxidizable substrates because light, which is necessary to cause the catalyst to be a source for singlet oxygen, is able to penetrate only a comparatively short distance into the reaction mixture.