Synthesis and evaluation of the biodegradability potential of Cholinium-based ionic liquids and deep eutectic solvents

Ionic Liquids (ILs) and Deep Eutectic Solvents (DESs) are two promising classes of solvents, often labeled as “green” alternatives to conventional organic solvents due to their tunable physicochemical properties. In this study a series of six DESs and nine ILs were successfully synthesized, structurally characterized by 1 H NMR spectroscopy, and assessed for their biodegradability via the BOD 5 closed-bottle test. All the synthesized solvent systems, share the same structural feature of a cholinium cation, whereas a series of carboxylic acids was used to act either as counterion (in the case of protic ILs) or the hydrogen bond donors (in the case of DES). Despite the growing interest in green solvents, to our knowledge, no prior studies were set to examine and compare the biodegradability of ILs and DESs formed from the same or structurally similar components. Among the ILs and DESs, biodegradability rates reached up to 81.3 % and 86.1 % respectively. Five ILs (IL 2-3 and IL 6–9 ) and two DESs (DES 4 and DES 6 ), exceeded 60 % biodegradability within five days, surpassing the OECD's 28-day threshold for classification as “readily biodegradable.” The BOD results indicate that ILs and DESs composed by the same starting materials tend to exhibit varying biodegradability rates, possibly due to different molecular interactions existing in the systems (mainly ionic and electrostatic interactions in ILs and hydrogen bond and Van der Waals interactions in DES). Overall, the results demonstrate that the majority of the synthesized solvents were found to be readily biodegradable. • Synthesis and structural characterization of cholinium-based ILs and DESs. • Biodegradability assessment (BOD 5 method) of cholinium-based ILs and DESs. • Biodegradability reached up to 81 % for ILs and 86 % for DESs. • Study of the effect of structural features on IL and DES biodegradability.