1, 3‐Bis(2′‐hydroxyethyl)imidazolium ionic liquids: correlating structure and properties with anion hydrogen bonding ability. (5th September 2013)

• Record Type: Journal Article
• Authors: Deng, Feng; Reeder, Zachary K.; Miller, Kevin M.
• Is Part Of: Journal of physical organic chemistry. Volume 27:Number 1(2014:Jan.)
• Page Start: 2
• Page End: 9
• Publication Date: 2013-09-05
• Subjects: Chemistry, Physical organic -- Periodicals; 547.1
• DOI: 10.1002/poc.3198
• Languages: English
• ISSNs: 0894-3230

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>A series of 1, 3‐bis(2′‐hydroxyethyl)imidazolium <named-content id="d441e816" content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">ionic liquids</named-content> is reported where <sup>1</sup>H NMR chemical shift values and thermal stabilities (<italic>T</italic><sub>d</sub>), as determined by thermogravimetric analysis, are correlated with the hydrogen bonding capability of various anions ([Cl<sup>−</sup>], [Br<sup>−</sup>], [CF<sub>3</sub>CO<sub>2</sub><sup>−</sup>], [NO<sub>2</sub><sup>−</sup>], [MsO<sup>−</sup>], [NO<sub>3</sub><sup>−</sup>], [TfO<sup>−</sup>], [BF<sub>4</sub><sup>−</sup>], [NTf<sub>2</sub><sup>−</sup>], and [PF<sub>6</sub><sup>−</sup>]). Use of anions with the strongest hydrogen bonding capability, such as chloride [Cl<sup>−</sup>], bromide [Br<sup>−</sup>], and trifluoroacetate [CF<sub>3</sub>CO<sub>2</sub><sup>−</sup>], led to the furthest observed downfield chemical shift values in DMSO‐d<sub>6</sub> and the poorest thermal stabilities ([CF<sub>3</sub>CO<sub>2</sub><sup>−</sup>] < 200 °C). Thermal stabilities in excess of 350 °C and upfield chemical shift values were observed for <named-content id="d441e901" content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">ionic liquids</named-content>, which employed the weakly coordinating triflate [OTf<sup>−</sup>], tetrafluoroborate [BF<sub>4</sub><sup>−</sup>], or bis(trifluoromethylsulfonyl)imide [NTf<sub>2</sub><sup>−</sup>] anion. Optimized structures of selected <named-content id="d441e921" content-type="chemicalTechnology" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink">ionic liquids</named-content>, as determined by density functional theory calculations at the B3LYP/6‐31G + (d, p) level, indicated that the anion preferred to be located above the imidazolium ring and in close proximity to the hydroxyl groups. Calculated dissociation energies (<italic>Δ</italic>E) and a comparison of key bonding distances (C2―H, (C2)H···X, O―H, and (O)H···X) also confirmed this structural preference. Copyright © 2013 John Wiley & Sons, Ltd.</p> </abstract>