Synthesis and Thermal Stability of Pyridinium Ionic Liquids with the Bromotrichloroferrate Anion

Ionic liquids based on 1-alkylpyridinium bromotrichloroferrates(III), [C5H5N–R]+[FeCl3Br]–, where R = H, C2H5, C4H9, C6H13, C8H17, C10H21, C12H25, and C16H33, were synthesized. The compounds were characterized using infrared and visible spectroscopy. Their thermal stability in air was investigated over the temperature range of 25–600°C and compared with that of the corresponding 1-alkylpyridinium bromides. The effects of alkyl chain length in the cation and the nature of the anion on the thermal stability of the ionic liquids were systematically analyzed. The results reveal clear structure–property relationships governing the thermal behavior of these materials.