Improved synthesis of perfluoroalkyl substituted 1,3,4-oxadiazoles as precursors for corresponding 1,2,4-triazoles

An improved and more efficient synthesis of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole (2a), 2,5-bis (perfluoroethyl)-1,3,4-oxadiazole (2b), 2-(perfluoroethyl)-5-(trifluoromethyl)-1,3,4-oxadiazole (2d) and 2-(perfluoroheptyl)-5-(trifluoromethyl)-1,3,4-oxadiazole (2e), via ring-opening reactions of the corresponding sodium 5perfluoroalkyltetrazolates (10a-b) is described. Furthermore the named perfluoroallcyl-1,3,4-oxadiazoles (2a-b & 2d) were converted into the corresponding 3,5-bis(trifluoromethyl)-1,2,4-triazole (1a), 3,5-bis(perfluoroethyl)-1,2,4-triazole (Ib) and 5-(perfluoroethyl)-3-(trifluoromethyl)-1,2,4-triazole (Id), by in situ produced ammonia (urea and potassium hydroxide). All products were characterized using multinuclear (H-1, C-13, F-19) NMR spectroscopy and differential scanning calorimetry to determine the structure and thermodynamic characteristics. Additionally, the molecular structure of la was determined by single crystal X-ray diffraction. (C) 2016 Elsevier B.V. All rights reserved.