This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013 New J. Chem., 2013, 37, 1461--1469 1461 Cite this: New J. Chem., 2013, 37, 1461 Azolium azolates from reactions of neutral azoles with 1,3-dimethyl-imidazolium-2-carboxylate, 1,2,3-trimethyl-imidazolium hydrogen carbonate, and N,N-dimethyl-pyrrolidinium hydrogen carbonate† Marcin Smiglak,z C. Corey Hines,y W. Matthew Reichert,z Julia L. Shamshina, Preston A. Beasley, Parker D. McCrary, Steven P. Kelley and Robin D. Rogers* Utilizing previously reported synthetic protocols for the halide- and metal-free synthesis of organic salts, we have prepared a new group of imidazolium and pyrrolidinium azolate anion-based salts demonstrating the general applicability of the methodology and expanding our investigation into non ion exchange routes to potentially energetic ionic liquids. Eighteen salts, out of which six exhibit melting points below 100 1C, were prepared by a simple decarboxylation reaction, which resulted in clean formation of the new compounds without the need for extensive purification. The low stability of the H 2 CO 3 by-product, and its decomposition to CO 2 and H 2 O in aqueous media, allows for purification of the salts by evaporation only. Introduction A group of organic azolate anions (e.g., imidazolates, triazolates, and tetrazolates) was recently introduced into the field of ionic liquids (ILs, now defined as salts that melt below 100 1C) allowing for a similar degree of facile functionalization of anions, in a manner similar to the modifications of the well- studied azolium cations. 1–10 One of the first examples using azolate anions in the synthesis of ILs, was presented by Ohno et al., 1 with the reaction of 1-ethyl-3-methylimidazolium hydroxide and neutral 1,2,4-triazole or tetrazole forming 1-ethyl-3-methyl- imidazolium 1,2,4-triazolate (T g = À76 1C) and 1-ethyl-3-methyl- imidazolium tetrazolate (T g = À89 1C). Our group has been interested in azolate-based ILs in our continuing work towards development of general design strategies for the formation of energetic ionic liquids (EILs), and we have reported formation of stable azolate anion-based salts by combination of such anions with a variety of IL forming cations. 4,5,11 Our original study concentrated on pairing, through metathesis reactions, of substituted imidazolate, triazolate, tetrazolate, benzimidazolate, and benztriazolate anions with common quaternary ammonium, imidazolium, pyridinium, and phos- phonium cations to allow for screening of the influence of the anion structure on the physical properties of the resulting salts. 11 Thermogravimetric analysis (TGA) revealed that the azolate anions allow for the formation of highly stable salts with decomposition temperatures as high as 235 1C (for tetra- methylammonium 3,5-dinitro-1,2,4-triazolate). The results suggested that higher substitution of the azolate anion with electron withdrawing groups, in addition to high nitrogen content in the heterocycle, leads to a better charge delocaliza- tion in the anion and, consequently, its thermal stability. 11 We also found that combination of a common IL forming cation, 1-butyl-3-methylimidazolium [1-Bu-3-Me-Im] + , with substituted azolate anions resulted in salts with very low melting points; the lowest melting salt being 1-butyl-3-methylimidazolium tetrazolate with only a glass transition at À82 1C. 5 Shreeve et al. 6,7,12 and Klapotke et al. 2 have recently reported a wide range of energetic azolate-based salts with some examples reaching melting points of only 61 1C (for 1-propyl-4-methyl- 1,2,4-triazolium 3,5-dinitro-1,2,4-triazolate), or glass transitions as low as À43 1C (for 1-(2-azidoethyl)-4-methyl-1,2,4-traizolium 3,5-dinitro-1,2,4-triazolate). In their research, new azolate anions were developed and used for the synthesis of ILs including 5-nitro-tetrazolate, 3,5-dinitro-pyrazolate, and 5,5 0 -azo-tetrazolate. Center for Green Manufacturing and Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487, USA. E-mail: rdrogers@as.ua.edu † CCDC 902237–902240. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c3nj00147d ‡ Current Address: Poznan Science and Technology Park, Poznan, Poland § Current Address: Nuclear Radiation Center Washington State University, Pullman, WA 99164, USA ¶ Current Address: Department of Chemistry, University of South Alabama Mobile, AL 36688, USA Received (in Porto Alegre, Brazil) 6th February 2013, Accepted 18th February 2013 DOI: 10.1039/c3nj00147d www.rsc.org/njc NJC PAPER Downloaded by University of Alabama at Tuscaloosa on 30/04/2013 21:45:53. Published on 20 February 2013 on http://pubs.rsc.org | doi:10.1039/C3NJ00147D View Article Online View Journal | View Issue