Base stable quaternary ammonium ionic liquids

Abstract

Ionic liquids with the bis(2-ethylhexyl)dimethylammonium cation, [BEDMA] + , were prepared by a halidefree route starting from the readily available secondary amine bis(2-ethylhexyl)amine. The following anions were considered: chloride, bromide, iodide, nitrate, hydrogensulphate, dihydrogenphosphate, formate, acetate, propionate, trifluoroacetate, methyl sulphate, methanesulphonate, tosylate, isonicotinate, nicotinate and picolinate. Several of the compounds are room-temperature ionic liquids, albeit with a high viscosity. All ionic liquids are soluble in water. The ionic liquids are very stable in strongly alkaline medium. No signs of decomposition could be observed by contact of the chloride ionic liquid with 50 wt% sodium hydroxide, even after prolonged heating at 80 C. The high stability against strong bases is attributed to the branched structure of the quaternary ammonium cation, which blocks the Hofmann elimination reaction.

Multi‐Gram Scale Synthesis of 1,2,3‐Triazolium Ionic Liquids and Assay of Their Resistance towards Bases

“…However, the stability of the n ‐hexyl side chain and the sensitivity of the 2‐ethylhexyl side chains in [HHT][Tf 2 N] and [EhEhT][Tf 2 N] cannot be explained by a simple E2 decomposition mechanism. This differs from what is observed for quaternary ammonium ionic liquids . Furthermore, only the side chain adjacent to the methyl group appears susceptible to elimination in [EhEhT][Tf 2 N], selectively yielding the precursor triazole and 2‐ethylhexanol as decomposition products.…”

“…To investigate the dependence of the stability towards bases on the nature of the side chain, we have synthesized peralkylated 1,2,3‐triazolium ionic liquids with linear and branched alkyl chains located on the N1‐ and N3‐positions. As reported by Lethesh and coworkers, branching at the β‐position is effective at sterically inhibiting Hofmann elimination, should this process occur …”

“…Ionic liquids are generally solvents with wide electrochemical windows, making them resistant to oxidation and reduction, However, the cations of most ionic liquids are susceptible to attack by strong Brønsted bases, precluding their use in combination with strong alkalis and rendering them poor solvents for reactions involving organometallic reagents. Quaternary ammonium ionic liquids degrade via a β‐elimination reaction known as the Hofmann elimination, affording an alkene and the corresponding amine . Phosphonium ionic liquids, while structurally analogous to quaternary ammonium ionic liquids, decompose through an entirely different mechanism, involving the attack of hydroxide ions at the phosphorus center, eventually forming a phosphine oxide and an alkane , .…”

“…Ionic liquids based on the bis(2‐ethylhexyl)dimethylammonium cation have shown excellent stability in 50 wt.‐% NaOH. However, the resulting ionic liquids are all very viscous and water‐soluble, making them rather unsuited as reaction media and extractants . For similar reasons, long‐chain phosphonium ionic liquids are also compatible with strong bases without the formation of phosphine oxides .…”

Extraction of naphthenic acid from highly acidic oil using phenolate based ionic liquids

“…The phenolate anions were used because of their high basicity and the presence of p electrons, which can enhance the de acidification process. Binnemans et al used phenolate anion with a tert-Butyl group at para position in combination with various cations for the development of a simple method for the synthesis of hydrophilic ionic liquids with very low halide content and highly base stable ammonium ionic liquids [18,19]. Phenolate ionic liquids with tetraalkylphosphonium cation has been used for CO 2 capture [20].…”