Quality conversion of H2S into β-mercaptopropionic acid by CETSA-based ionic liquid

With respect to the detrimental hydrogen sulfide (H2S), a whole new range of hydrophilic ionic liquids (ILs) could conveniently catalyze into more widely needed chemical reagents. ILs could be beneficial to increase the solubility and ionization of H2S, resulting in the Michael addition reaction with acrylic acid to produce β-mercaptopropionic acid. In this study, four kinds of hydrophilic ILs were synthesized by using carboxyethiosuccinic acid (CETSA), which contains three carboxyl groups with different chemical properties, as anions and combined with basic cations. The effect of the structure and reaction conditions of ILs on the catalytic activity of the system was studied. The result showed that the CETSA-based ILs with N, N, N′, N' -tetramethyl-1, 6-hexamethylenediamine (TMHDA) as cation had the best catalytic effect. ILs catalyst can greatly improve the selectivity and yield of the target product in addition reaction, which could be used for eight times at least without a noticeable decrease in its activity and conversion. In the absence of H2S cylinders, the conversion of acrylic acid can reach 99.21%, and the selectivity and yield of mercaptopropionic acid can reach 92.57% and 91.84% with [TMHDAH]CETSA. The ILs was characterized by FTIR, 1H NMR, 13C NMR and MS in order to determine the structure of the ILs. The thermal stability of ILs in the reaction system was observed by TG and DSC, and the ionization of ILs in solvent was measured by pH meter.