Electronic Effects of para-Substitution on the Melting Points of TAAILs

• Published in: Chemistry, an Asian journal an Asian journal, 2011-03, Vol.6 (3), p.863-867
• Main Authors: Schulz, Tobias, Ahrens, Sebastian, Meyer, Dirk, Allolio, Christoph, Peritz, Anke, Strassner, Thomas
• Format: Article
• Language: English
• Subjects: Chemistry; computational chemistry; electronic effects; electrostatic interactions; ionic liquids; Ions; Solvents; taail
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201000744

Owing to numerous new applications, the interest in “task‐specific” ionic liquids increased significantly over the last decade. But, unfortunately, the imidazolium‐based ionic liquids (by far the most frequently used cations) have serious limitations when it comes to modifications of their properties. The new generation of ionic liquids, called tunable aryl–alkyl ionic liquids (TAAILs), replaces one of the two alkyl chains on the imidazolium ring with an aryl ring which allows a large degree of functionalization. Inductive, mesomeric, and steric effects as well as potentially also ππ and ππ+ interactions provide a wide range of possibilities to tune this new class of ILs. We investigated the influence of electron‐withdrawing and ‐donating substituents at the para‐position of the aryl ring (NO2, Cl, Br, EtO(CO), H, Me, OEt, OMe) by studying the changes in the melting points of the corresponding bromide and bis(trifluoromethanesulfonyl)imide, (N(Tf)2−), salts. In addition, we calculated (B3LYP/6‐311++G(d,p)) the different charge distributions of substituted 1‐aryl‐3‐propyl‐imidazolium cations to understand the experimentally observed effects. The results indicated that the presence of electron‐donating and ‐withdrawing groups leads to strong polarization effects in the cations. Spotlight on TAAILs: This article describes the influence of electron‐donating‐ and electron‐withdrawing substituents in the para‐position of the aromatic ring on the melting points of tunable aryl alkyl ionic liquids (TAAILs).