A series of 4-benzyl-4-methylmorpholinium salts have been synthesized producing morpholinium ionic liquids with inorganic (chloride, nitrate, tetrafluoroborate, hydrogen sulphate) and organic (formate, acetate, methoxyacetate, 2-(2-methoxyethoxy)acetate, hexanoate, octanoate, dodecyl sulphate, 2-ethylbutyrate, lactate, crotonate, maleate, salicylate, saccharinate) anions. Their physicochemical properties, cytotoxicity to the promyelocytic leukaemia rat cell line IPC-81, oral toxicity and biodegradability were determined. The anion significantly determined the state of aggregation and cytotoxicity. The results enabled 4-benzyl-4-methylmorpholinium ionic liquids to be classified as being of moderate or low toxicity (EC50 between 0.15 and 14.13 mM). The acute toxicity for 4-benzyl-4-ethylmorpholinium acetate is between 300–2000 mg kg−1b.w. in female rats. The activity of these morpholinium salts against bacteria and fungi was very low. It was found that new 4-benzyl-4-methylmorpholinium-based ionic liquids with anions commonly used for dissolving cellulose, such as formate or acetate, can also be used as new biomass solvents.
