Carbamate salt ionic liquid

Another approach to polymer/catalyst separation is to replace the use of costly wasteful solvents with a procedure that produces little to no waste, and requires no catalyst modification. These switchable polarity solvents (SPS), as developed by Jessop and coworkers, are able to utilize the reaction of secondary amines with C02 to reversibly form carbamate salt ionic liquids (Scheme 8.10) [66]. Upon the completion of the polymerization reaction, EtBuNH (Et = ethyl, Bu = n-butyl) is added to dissolve the polymer/catalyst mixture. The subsequent bubbling of C02 through this solution results in a precipitation of the polymer product, such that the purified polymer can be isolated by simple filtration. The catalyst can then be recovered by distilling the amine/carhamate mixture, and the entire system can (in theory) be recycled (Scheme 8.11). 

Upon dissolving the copolymer/catalyst mixture in ethylbutylamine (EtBuNH) the introduction of CO2 at atmospheric pressure results in formation of an equilibrium mixture of carbamic acid and the quaternary ammonium salt of carbamate. The carbamic acid serves to remove the copolymer from the metal center, at which time it precipitates in the ionic liquid and is isolated by filtration. The metal catalyst... 

Two general classes of ionic liquids which are easily distilled are protic ionic liquids (PILs) formed by reaction between a volatile acid and base [86], and dialkylammo-nium carbamate salts such as dimethylammonium dimethylcarbonate (DIMCARB) [72, 73, 206], An example of a distillable PIL is methylpyrrolidinium acetate formed from the exchange of a proton between acetic acid and methylpyrrolidine [86], DIMCARB, a low-cost ionic liquid produced by mixing C02 with dimethylamine, has been used as a reaction medium for the synthesis of monoarylidene and macro-cyclic compounds, where in each case, the product was separated by distillation of the ionic liquid [72, 73, 206],... 

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