Lichtinitiierte polymer- und polymerisationsreaktionen, 26. Elektrophile ringöffnungsreaktionen zwischen glycidylethern und ketonen oder aldehyden initiiert durch photoinitiatorsysteme

By the irradiation of benzoin derivatives in the presence of arene diazonium salts or aryl iodonium salts cationic species are formed, which initiate ring-opening reactions of 2,3-epoxy-propyl (glycidyl) ethers in the presence of ketones or aldehydes. 1,3-Dioxolane formation dominates over homopolyaddition reactions of glycidyl ethers. This method forms dioxolane in satisfactory preparative yields. The quantum yields of disappearance of phenyl glycidyl ether in acetone (Φ_PGE) were measured in dependence of some system parameters. By the photolysis of benzil dimethyl ketal more catalytic species are produced as in the case of benzoin isopropyl ether or α-phenylbenzoin. The Φ_PGE values for diazonium salts are higher than for iodonium salts, with triphenylsulfonium salts the reaction failed. With the anions of iodonium salts the following sequence for Φ_PGE is observed: SbF₆^? > PF₆^? ? SbCl₆^? = BF₄^? = 0. Because the key step of the catalyst formation is an electron transfer reaction between radicals produced by the photolysis and the onium ions, the concentration of the salts influences Φ_PGE. Phenyl glycidyl ether reacts more rapidly than 2,2-bis(4-hydroxyphenyl)trimethylene diglycidyl ether and isobutyl glycidyl ether.