Deep eutectic solvents (DES) are generally composed of two or three cheap and safe components that are associated with each other via hydrogen bonds. The formation Caprolactam (CPL)-tetraalkyl ammonium halide (TAAX) DES and its hydrate were investigated using React IR. TAAX was introduced to CPL in the molten state at 353.15 K, the intermolecular H-N-C=O⋯H-N-C=O hydrogen bonds (CPL dimer) transfer to X-⋯H-N-C=O (CPL-TAAX DES). When water was added to CPL-TAAX DES, intermolecular X-⋯H-N-C=O⋯H-O-H hydrogen bonds appeared, and CPL-TAAX DES hydrate was formed. However, if the ratio of water exceeded the moral fraction of 0.61, CPL-TAAX DES hydrate turned into a CPL-TAAX aqueous solution. The CO (1660 cm-1) bonds were linearly correlated with hydrogen bonds number and TBAB amount in CPL-TBAB DES. When the molar fraction of CPL-TBAB DES was 0.39 to 0.78, the CO peak redshift has a better linear correlation with water. Halide anions and the alkyl chain length of TAAX have little influence on the redshifts and peak intensity of the CO peak.
Keywords: CPL; DES; Hydrate; TBAB; Water.
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