Ionic liquid S-alkylthiouronium salts

The preparation and characterisation of a series of ionic liquids based on S-alkylthiouronium cations prepared from thiourea, 1,3-dimethylthiourea, 1,3-diethylthiourea and 1,3-tetramethylthiourea coupled with bis{(trifluoromethane)sulfonyl}imide, bromide, methylsulfate or ethylsulfate anions are reported. All are liquids at room temperature or solids with melting points close to room temperature, except for the bromide salts, which have melting points below 92 °C. Systematic variation in the N- and S-alkyl substituents demonstrates how the physical properties of these ionic liquids can be readily controlled. The mutual miscibility limits of representative examples with octane, dodecane and toluene have been determined as a function of temperature, and the extraction of dibenzothiophene from dodecane as a model for desulfurisation of diesel has been investigated.