The photoaddition of 4‐methyl‐1,2,4‐triazoline‐3,5‐dione (4‐MTAD) with a wide variety of acyclic, cyclic and crown aliphatic ethers has been investigated. Monochromatic (λ = 514.5 nm) or polychromatic (λ ≥ 310 nm) irradiations give identical mono‐urazolyl ethers as reaction products. Unsymmetrical acyclic ethers afford a mixture of the two α and α′ mono‐urazolyl ethers. In the case of 12‐crown‐4, mono and di‐substituted products are obtained. ESR experiments and quantum calculations at the AM1 and 6‐31G* levels were performed and a possible reaction mechanism is proposed in which the most probable photochemical process is the H‐abstraction leading to a urazolyl radical.
Matrix-isolated 4-methyl-1,2,4-triazolinedione 1a and 4-phenyl-1,2,4-triazolinedione 1b were photolyzed at lambda >/= 335 nm and lambda >/= 310 nm, respectively. The reactions induced by photolysis were monitored by FT-IR spectroscopy. The isocyanates 2a and 2b are always the more abundant products with carbon monoxide. Methyl- and phenylaziridine-2,3-diones (3a and 3b) were detected as minor, but well-identified reaction products. The IR experimental absorption bands were assigned by comparison with literature data and with simulated infrared spectra obtained by ab initio calculation at the 6-31G level. Stable at the matrix temperature (10 K), 3a and 3b photolyzed to isocyanates and CO when irradiated at lambda >/= 230 nm. Irradiation of 2b at this wavelength induces its decomposition. The kinetic data show that the rate constant process 1a --> 2a is faster than the 1a --> 3a process (3.29 x 10(-)(3 )and 2.35 x 10(-)(4)min(-)(1) respectively).
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