Synthesis of N-cyanoalkyl-functionalized imidazolium nitrate and dicyanamide ionic liquids with a comparison of their thermal properties for energetic applications
作者:David M. Drab、Marcin Smiglak、Julia L. Shamshina、Steven P. Kelley、Stefan Schneider、Tommy W. Hawkins、Robin D. Rogers
DOI:10.1039/c0nj00889c
日期:——
The synthesis of 10 N-alkyl-N-cyanoalkyl-functionalized imidazolium (N-methyl- and N-butyl-N-((CH2)nCN)imidazolium; n = 1–4) nitrate and 11 N-alkyl-N-cyanoalkyl-functionalized imidazolium (N-methyl-N-((CH2)nCN)imidazolium; n = 1–6, N-(2-cyanoethyl)-N-((CH2)nCN)imidazolium; n = 1,3–6) dicyanamide salts was achieved via N-alkylation of substituted imidazoles with commercially available haloalkylnitriles followed by anion exchange. Based on their observed melting points, all dicyanamide salts and all but one nitrate salt (1-cyanomethyl-3-methylimidazolium nitrate) had melting points <100 °C, as did 13 of the 17 halide precursors also reported here. Differential scanning calorimetry data indicated that melting points decreased by increasing the N-alkyl or N-cyanoalkyl chain length or by exchanging with the dicyanamide anion, which produced the lowest melting points in comparison to analogous halide or nitrate salts. Thermogravimetric analyses indicated that thermal stability increased for longer N-cyanoalkyl substituent lengths and decreased significantly for nitrates and more so for dicyanamides bearing short-chain N-cyanoalkyl substituents (e.g., N-cyanomethyl, N-(1-cyanoethyl), and N-(2-cyanoethyl)) in comparison to halide precursors. Furthermore, for many of the N-cyanoalkyl-substituted salts (especially the dicyanamides), there was a significant production of thermally-stable char – presumably due to by-products formed from the reaction of either N-cyanoalkyl substituents, dicyanamide anion, or both, which resulted in thermally-stable polymers or cycles.
通过将市售的卤代烷基腈与取代咪唑进行N-烷基化反应,然后进行阴离子交换,成功合成了10种N-烷基-N-氰基烷基功能化的咪唑鎓(N-甲基-和N-丁基-N-((CH2)nCN)咪唑鎓;n = 1–4)硝酸盐和11种N-烷基-N-氰基烷基功能化的咪唑鎓(N-甲基-N-((CH2)nCN)咪唑鎓;n = 1–6,N-(2-氰乙基)-N-((CH2)nCN)咪唑鎓;n = 1,3–6)二氰胺盐。根据它们的熔点观测结果,所有二氰胺盐和除一种硝酸盐(1-氰甲基-3-甲基咪唑鎓硝酸盐)外的所有硝酸盐的熔点均低于100 °C,这里还报道的17种卤化物前体中也有13种的熔点低于100 °C。差示扫描量热数据表明,熔点随着N-烷基或N-氰基烷基链长的增加或与二氰胺阴离子交换而降低,这使得与类似的卤化物或硝酸盐相比熔点最低。热重分析显示,随着N-氰基烷基取代基长度的增加,热稳定性增加,而对于硝酸盐和特别是短链N-氰基烷基取代基(例如,N-氰甲基,N-(1-氰乙基)和N-(2-氰乙基))的二氰胺盐,热稳定性显著降低。此外,许多N-氰基烷基取代的盐(尤其是二氰胺盐),存在大量热稳定的炭质产物——这可能是由于N-氰基烷基取代基、二氰胺阴离子或两者的反应产物形成了热稳定的聚合物或环。