Ionic liquid-assisted carboxylation of amines by CO2: a mechanistic consideration

Abstract

The catalytic roles of ionic liquids (ILs) in the syntheses of 1,3-disubstituted ureas from the carboxylation of amines by CO(2) were experimentally and theoretically investigated. The carboxylation reaction of n-butylamine was greatly facilitated by the presence of an IL and the catalytic activity of the IL was strongly affected by the nucleophilicity of the anion. Computational study on the mechanistic aspects of the carboxylation with methylamine with or without the presence of an IL, 1-ethyl-3-methylimidazolium chloride, implies that the activation energies of the transition states and the intermediate ionic species could be lowered significantly through the multi-interactions of the carbonyl group of CO(2) with both cations and anions of the ILs.

Significant Cation Effects in Carbon Dioxide–Ionic Liquid Systems

“…[46] Surprisingly, the CDF in Figure 3 B clearly shows that the closer the solute is to the cation, the less bent it is, as for the lower C(CO 2 )–C2 distances there are no entries corresponding to lower O–C–O angles of the solute. Thus, instead of cooperation, competition is indicated between the anion and the cation for interacting with the CO 2 .…”

Carbon dioxide uptake as ammonia and amine carbamates and their efficient conversion into urea and 1,3-disubstituted ureas

“…In recent years the direct synthesis of substituted ureas has been accomplished with the non toxic and cheap carbon dioxide in the presence of different catalysts and dehydrating agents to increase the yield of reaction [39][40][41][42]. Ionic liquids in conjunction with a base (CsOH) or transition metal (Fe, Co, Ni, Cu, Zn) acetates were also employed as reaction medium and catalysts to obtain 1,3-disubstituted ureas in good yield [43][44][45][46]. However, most catalysts can be reused no more than 3-4 times.…”

Organic Base-Catalyzed C–S Bond Construction from CO2: A New Route for the Synthesis of Benzothiazolones

“…The product yield increased in the following order: dimethyl sulfoxide (DMSO) < CH 3 CN < N,N-dimethylformamide (DMF) < 1-methyl-2-pyrrolidinone (NMP) ( Table 1, entries 5,[10][11][12]. This corresponded with the order of CO 2 solubility in these solvents (expressed as Henry's constant), DMSO (12.67) > CH 3 CN (9.049) > DMF (7.966) > NMP (7.61) [41]. Based on the CO 2 solubility in various solvents being expressed as Henry's constants, it was concluded that the yield of benzothiazolone increased as Henry's constant decreased.…”

“…Methyl-substituted lower reactivity, and the yields of the substituted substrates with neither electron-withdrawing groups nor electron-donating groups were also lower than the model reaction. Based on previous reports and the experimental results [28,33,41,42,45], a probable catalytic cycle was proposed for the reaction of 2-aminothiophenols with CO 2 to benzothiazolones using DBN as a catalyst, as depicted in Scheme 2. Firstly, CO 2 could react with DBN to form the key carbamate Based on previous reports and the experimental results [28,33,41,42,45] …”