Trapping of benzene oxide-oxepin and methyl-substituted derivatives with 4-phenyl- and 4-pentafluorophenyl-1,2,4-triazoline-3,5-dione

4-Phenyl-1,2,4-triazoline-3,5-dione and its pentafluoro analogue are efficient reagents for trapping arene oxides, e.g. benzene oxide-oxepin, affording crystalline adducts that can be quantitatively analysed by HPLC and MS techniques.