Molecular structure, vibrational spectra and photochemistry of 5-mercapto-1-methyltetrazole

In this work, 5-mercapto-1-methyltetrazole was studied by low temperature matrix-isolation and solid-state infrared spectroscopy, DFT(B3LYP)/6-311++G(d,p) calculations and photochemical methods. In the low temperature neat solid phase and isolated in an argon matrix, the compound was found to exist in the 1-methyl-1,4-dihydro-5H-tetrazole-5-thione tautomeric form. The infrared spectra of the compound were fully assigned and correlated with structural properties. In situ UV-irradiation (λ>235 nm) of the matrix-isolated monomer is shown to induce different photochemical processes, all of them involving cleavage of the tetrazole ring: e.g. (1) molecular nitrogen expulsion, with production of 1-methyl-1H-diazirene-3-thiol, which is produced in two different conformers; (2) ring cleavage leading to production of methyl isothiocyanate and azide; (3) simultaneous elimination of nitrogen and sulphur with production of N-methylcarbodiimide. Following these photoprocesses, subsequent reactions occur, leading to production of methyl diazene, carbon monosulphide and nitrogen hydride. Spectroscopic evidence of the production of the above-mentioned chemical species is provided.