PHOTOLYSIS OF MATRIX-ISOLATED 4-R-1,2,4-TRIAZOLINE-3,5-DIONES - IDENTIFICATION OF AZIRIDINE-2,3-DIONE TRANSIENTS

Matrix-isolated 4-methyl-1,2,4-triazolinedione 1a and 4-phenyl-1,2,4-t riazolinedione 1b were photolyzed at lambda greater than or equal to 3 35 nm and lambda greater than or equal to 310 nm, respectively. The re actions induced by photolysis were monitored by FT-IR spectroscopy. Th e isocyanates 2a and 2b are always the more abundant products with car bon monoxide. Methyl- and phenylaziridine-2,3-diones (3a and 3b) were detected as minor, but well-identified reaction products. The IR exper imental absorption bands were assigned by comparison with literature d ata and with simulated infrared spectra obtained by ab initio calculat ion at the 6-31G level. Stable at the matrix temperature (10 K), 3a a nd 3b photolyzed to isocyanates and CO when irradiated at lambda great er than or equal to 230 nm. Irradiation of 2b at this wavelength induc es its decomposition. The kinetic data show that the rate constant pro cess 1a --> 2a is faster than the 1a --> 3a process (3.29 x 10(-3) and 2.35 x 10(-4) min(-1) respectively).