Preparation and characteristics of dehydrated ricinoleic acid by ionic liquid catalysis

Effects of N-methylimidazole hydrogen sulfate, 2-pyrrolidone hydrogen sulfate, N-methyl pyrrolidone hydrogen sulfate, and their -SO 3 H functionalized acidic ionic liquids were comparatively investigated on the dehydration degree of ricinoleic acid (RA) sample and conjugated linoleic acid (CLA) content in the resulting dehydrated ricinoleic acid (DRA) sample. Results showed the -SO 3 H functionalized N-methyl pyrrolidone hydrogen sulfate ([C 3 SO 3 Hnmp]HSO 4 ) had the strongest catalytic activity among the six ionic liquids. Under the optimal conditions (4 % [C 3 SO 3 Hnmp]HSO 4 , 250 °C, and 30 min), the dehydration degree of RA sample reached 98.69 % with 42.57 % of CLA in the resulting DRA sample. Results from nuclear magnetic resonance, Fourier transform infrared spectroscopy, and mass spectrometry indicated the hydroxyl group of RA underwent intramolecular dehydration to form new double bonds; RA sample was randomly dehydrated with both non-conjugated linoleic acid and CLA present in DRA sample. Rheological analysis showed that RA sample had a higher viscosity than DRA sample due to the presence of hydrogen bonds. Thermogravimetric analysis showed RA and DRA samples were thermally stable at up to 250 °C.