Imidazolium and Pyridinium Ionic Liquids from Mandelic Acid Derivatives: Synthesis and Bacteria and Algae Toxicity Evaluation

Abstract

A new class of low bacterial and algal toxicity imidazolium and pyridinium halide ionic liquids (ILs), produced by a short synthesis from substituted mandelic acid derivatives is disclosed. Melting points for most of the ILs were above or close to 100 °C; however, one imidazolium example has a glass transition temperature below room temperature (RT; −3.3 °C). The series of 8 ILs enables an investigation of toxicity on modifying the heterocycle, aromatic ring substitution, ester group, and proximity of cation to aromatic ring present within mandelic acid constituent. Two pyridinium salts, methyl 2-(3,4-methylenedioxyphenyl)-2-pyridinium acetate, bromide salt and methyl 2-(3,4-methylenedioxyphenyl)-2-(2-pyridiniumacetoxy)acetate, bromide salt have low toxicity to all bacteria strains (including Vibrio fischeri), and freshwater green algae (C. Vulgaris and P. subcapitata) screened. All eight pyridinium and imidazolium ILs have low toxicity to Gram-positive (B. subtilis) and Gram-negative (E. coli, P. fluorescens, P. putida (CP1), and P. putgida (KT 2440)) bacteria strains, although a significant range in IC50 values was obtained. Mandelate derived ILs have EC50 (C. Vulgaris and P. subcapitata) values 103–107 higher (less toxic) than other C14–C18 ionic liquids previously reported.