Pharmaceuticals degradation by UV and UV/H2O2 treatments

The degradation by UV and UV/H 2 O 2 treatments of the pharmaceutical intermediate 5-methyl-1,3,4-thiadiazole-2-methylthiol (MMTD-Me) has been investigated and compared to that of its parent compound [5-methyl-1,3,4-thiadiazole-2-thiol (MMTD)] previously studied. The investigation has been carried out with a 17 W low pressure mercury lamp, at room temperature, with an initial MMTD-Me concentration of 1 mg/l and with a molar ratio H 2 O 2 /substrate of 100/1. The results show that: (i) the complete MMTD-Me removal is achieved within 60 and 20 minutes by UV and UV/H 2 O 2 treatment respectively; (ii) the UV only irradiation does not cause any MMTD-Me mineralization; (iii) the UV/H 2 O 2 treatment, after 4 hours, leads to a complete mineralization of MMTD-Me organic sulfur and to a partial mineralization of carbon and nitrogen (79 and 16% respectively). Degradation by-products identification, performed by HPLC-UV-MS, revealed that the UV only irradiation gives rise to the sequential transformation of MMTD-Me into two by-products one of which, the last one, accumulates in the solution. Conversely, the UV/H 2 O 2 treatment leads to the formation of two intermediate by-products that undergo further degradation with the breakdown of the thiadiazole ring. These results confirm the effectiveness of UV based processes, alone or in combination with H 2 O 2 , in degrading pharmaceutical intermediates.