(513cn) Ionic Liquids As Solvents for Nucleophilic Aromatic Substitution Reactions
Nucleophilic aromatic substitution (SnAr) reactions are a class of reactions that are industrially significant but difficult to perform. SnAr reactions require high temperatures, multiple electron-withdrawing groups attached to the aromatic ring, or catalysts to obtain any significant amounts of the desired product. The high temperatures required for the reactions, as well as the need to dissolve polar and nonpolar reactants, lead to the use of polar aprotic organic solvents which are often toxic and environmentally harmful. Ionic liquids (ILs) offer an alternative to traditional molecular solvents. ILs are compounds with low melting points and vanishingly low vapor pressures. A newly developed class of ILs is thermally stable beyond the temperatures required for the SnAr reactions: peraryl phosphonium bistriflimides. Due to the ionic and organic nature of ILs, they can dissolve all reactants. They also stabilize the charged transition state, lowering the activation energy for the reaction and consequently increasing the rate. In this work, we examine a SnAr reaction performed in an IL and compare the rate of the same reaction performed in traditional molecular solvents.