Relationship between structure and biodegradability of gemini imidazolium surface active ionic liquids

Three ester-containing gemini imidazolium surface active ionic liquids [1,4-bis(1-alkyl-oxypropyl-imidazolium)-butane dichloride], abbreviated as [peC n Bim 2 ]Cl 2 ( n  = 12, 14, 16), were synthesized from imidazole , 1,4-dibromobutane, 1-chloro-3-propanol, and various aliphatic carboxylic acids. Chemical structures of [peC n Bim 2 ]Cl 2 were confirmed by H-Nuclear magnetic resonance, Fourier transform infrared spectroscopy , and elemental analysis . Thermal properties of [peC n Bim 2 ]Cl 2 were studied with Thermogravimetric analysis and Differential scanning calorimetry . The micellization parameters, adsorption/aggregation properties, and thermodynamic parameters of [peC n Bim 2 ]Cl 2 were demonstrated using tensiometry, electrical conductivity. Critical micelle concentration values of [peC n Bim 2 ]Cl 2 aqueous solutions decreased with increasing the alkyl chain length (from C12 to C16). The formation of micelles was spontaneous, exothermic, and entropy-driven. Using OECD 301D, the aerobic biodegradation of nine gemini imidazolium SAILs ([peC n Bim 2 ]Cl 2 , [C n Pim 2 ]Br 2 , and [C n Bim 2 ]Br 2 ) and three monoimidazolium SAILs ([C n IM]Br) were systematically investigated to determine the relationship between biodegradation and structural elements of imidazolium SAILs. Aerobic biodegradation of twelve SAILs followed the decreasing trend: [peC n Bim 2 ]Cl 2  > [C n Pim 2 ]Br 2  > [C n IM]Br > [C n Bim 2 ]Br 2 . Gemini imidazolium SAILs with ester functional group ([C n Pim 2 ]Br 2 and [peC n Bim 2 ]Cl 2 ) showed much higher biodegradation rates than those of [C n IM]Br and [C n Bim 2 ]Br 2 . The location of ester group played an obvious role on biodegradation. Gemini SAILs containing ester group in the side alkyl chains ([peC n Bim 2 ]Cl 2 ) showed much higher biodegradation ratio than those of [C n Pim 2 ]Br 2 (ester functional group in spacer). [peC n Bim 2 ]Cl 2 could be classified as readily biodegradable. The biodegradability of gemini imidazolium SAILs increased with increasing the alkyl chain length.