Synthesis and Characterization of CL-PA Ionic Liquid

Abstract

Caprolactam is most commonly used in the production of Nylon 6 in industry and is generally produced from cyclohexanone by the Beckmann rearrangement. Orthophosphoric acid is generally used in fertilizer production and is produced through two processes: wet and dry. In this study, detailed characterization of CL-PA was carried out by synthesizing CL-PA ionic liquid from orthophosphoric acid (PA) and caprolactam (CL). FTIR, Raman and UV-Vis spectroscopic analyses reveal that a bond is formed between CL and PA. The thermal behavior of CL-PA ionic liquid was inspected by TGA and DSC. It has been observed that the decomposition temperature of CL-PA ionic liquid is different from that of the starting materials (CL and PA). It was disclosed by DSC analysis that CL-PA ionic liquid only has a glass transition temperature. The room-temperature CL-PA ionic liquid synthesized from solid CL with melting point of 70.34 ℃ and 85 wt.% PA did not show any melting or freezing point and the glass transition temperature was found to be −27 ℃. It was revealed that CL-PA ionic liquid was more thermally stable than CL which alone almost completely evaporated at about 197 ℃. As a result of FTIR analysis of CL-PA ionic liquid and its constituents, it was demonstrated that –NH peaks of CL disappeared in the CL-PA spectrum and the peak of C=O group shifted to a lower frequency (i.e., 1604 cm⁻1). In the Raman analysis of CL-PA and its constituents, it was observed that the asymmetric C=O bending vibration and C=O stretching vibration of CL disappeared in the CL-PA spectrum. In the UV spectrum, it was observed that the maximum absorbance of CL-PA ionic liquid varied with respect to that of CL.