PAPER www.rsc.org/greenchem | Green Chemistry Synthesis and properties of glycerylimidazolium based ionic liquids: a promising class of task-specific ionic liquids† Fabio Bellina,* a Alessandra Bertoli, b Bernardo Melai, b Francesca Scalesse, a Francesca Signori c and Cinzia Chiappe* a,b Received 8th December 2008, Accepted 27th January 2009 First published as an Advance Article on the web 25th February 2009 DOI: 10.1039/b821927c A series of task-specific ionic liquids (TSILs) based on glycerylimidazolium cations have been prepared by reaction of 1-chloropropanediol, a compound obtainable from glycerol (a widely available and in-expensive waste product), with the appropriate base (1-H-imidazole, 1,2-dimethylimidazole and 1-methyl-1-H-imidazole). The reaction of 3-(1H-imidazol- 1-yl)propane-1,2-diol with chloroalkanes, bromoalkanes and alkyl mesylates gave the corresponding salts which were characterized. The possibility to use these ILs in palladium catalyzed reactions was evaluated, evidencing good catalyst stability and a high recyclability. Introduction Currently, ionic liquids (ILs) are receiving great attention for application as innovative solvents or additives in a variety of different areas reaching from material synthesis to separation science as well as alternative reaction media. 1 However, despite promising results evidenced by the many studies in which they have been used as solvents, evidencing unique properties, their widespread application in process chemistry is still hampered by doubts generally related to some practical drawbacks: (i) cost and possible toxicological concerns, (ii) problems related to product isolation, and (iii) catalyst recovery. To overcome at least some of these drawbacks more recently functionalized ILs, the so-called Task-Specific ILs (TSILs), have been synthesized. 2 A range of different functional groups providing properties similar or identical to those of the major classes of organic solvents has been incorporated into IL cations, including vinyl and allyl, amine, amide, ether and alcohol, acid, urea and thiourea, fluorous chains, alkyne, phosphoryl, nitrile, thiols, and ferrocenyl groups. The functionalization of the anion has been also performed, and ILs based on metal carbonyls, alkylselenites, and functionalized borates were synthesized. 3 Some of these ILs have been used as solvents in selected metal catalyzed reactions, 4 evidencing that TSILs can favor the activation of the catalyst, generate new catalytic species, improve the stability of the catalyst. Moreover, properly designed TSILs are able to optimize immobilization and recyclability, a Dipartimento di Chimica e Chimica Industriale, via Risorgimento 35, 56126, Pisa, Italy. E-mail: bellina@dcci.unipi.it; Fax: +39 050 2219260; Tel: +39 050 2219334 b Dipartimento di Chimica Bioorganica e Biofarmacia, via Bonanno 33, 56126, Pisa, Italy. E-mail: cinziac@farm.unipit.it; Fax: +39 050 2219660; Tel: +39 050 2219669 c CNR-INFM Polylab, via Risorgimento 35, I-56126, Pisa † This paper was published as part of the themed issue of contributions from the Green Solvents – Progress in Science and Application conference held in Friedrichshafen, September 2008. facilitate product isolation, and influence the selectivity of the reaction. On the other hand, the unique physico-chemical properties of these salts, 5 and in particular their solubility or insolubility in organic and aqueous media, has suggested the possibility of using TSILs as soluble supports for organic synthesis. This novel liquid-phase strategy could embrace several possibilities: (a) supported catalysts, (b) supported reagents, and (c) suppor- ted substrates. 6 In particular, the alcohol-functionalized TSILs have been extensively studied as replacements for solid poly- mer supports in the heterogeneous-phase synthesis of organic molecules. Bazureau et al. 7 synthesized various polyoxy-alcohol- functionalized TSILs evidencing the potential of these salts as liquid supports in ionic liquid-phase Knovenagel reactions, 1,3-dipolar cycloaddition and in the generation of a small library of thiazolidines and 2-thioxotetrahydropyrimini-4-(1H)-ones. 8 Similarly, Miao and Chan utilized these TSILs as liquid supports for Suzuki coupling reactions, and demonstrated their advantage over conventional solution phase synthesis. 9 Interestingly, recent investigations evidence that the introduction of a hydroxyl group on the longer alkyl chain of the imidazolium cation decreases toxicity towards aquatic species. 10 As an extension of our research into ionic liquid systems arising from low cost renewable resources (possibly, from waste materials) we became interested in the use of ionic liquids containing two vicinal hydroxyl groups in reaction media and additives. These TSILs can be prepared by reaction of a proper base with 1-chloropropanediol, a commercial compound obtainable, as evidenced by a recent patent, 11 from glycerol. Nowadays, glycerol is generated as a by-product in the pro- duction of bio-diesel and it is estimated that if production of biodiesel increases as projected, glycerol will become widely available and inexpensive (eventually, even a possible waste product). 12 Herein, we wish to report a series of imidazolium based ILs (2–10) functionalized by a 2,3-dihydroxypropyl group evidenc- ing their potential uses as ligands and solvents for palladium(II)- catalyzed reactions. 622 | Green Chem., 2009, 11, 622–629 This journal is © The Royal Society of Chemistry 2009