Facile, high-yielding preparation of pyrrolidinium, piperidinium, morpholinium and 2,3-dihydro-1H-isoindolinium salts and ionic liquids from secondary amines

Abstract

High yield and purity heterocyclic ionic liquids can be obtained via the microwave irradiation of equimolar amounts of a secondary amine and of an α,ω-dibromoalkane (i.e., 1,4-dibromobutane, 1,5-dibromopentane, bis(2-bromoethyl)ether, or α,α′-dibromo-o-xylene) in water, in the presence of potassium carbonate, followed by anion exchange with lithium bis(trifluoromethanesulfonyl)imide, affording pyrrolidinum, piperidinium and morpholinium ionic liquids, respectively. Using this methodology, a large number of homologous ionic liquids can be prepared from a small number of readily available and relatively cheap starting materials, including a new class of ionic liquids based on the 2,3-dihydro-1H-isoindolinium ring system. Analysis (using SWOT and the GSK “greenness” assessments) of this synthetic method and comparison with current literature preparations reveals that this new method delivers significant benefits across a range of relevant parameters.