Halogen-free ionic liquids

Finally, research efforts to replace hexafluorophosphate (and other halogen-containing) ionic liquids by some cheap and halogen-free ionic liquids in the Rh-catalysed hydroformylation should be mentioned. The first attempts in this direction were made by Andersen et al. [10] These authors investigated the hydroformylation of... 

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

In recent times, the development of new ionic liquids has made great progress. Important developments include a range of new halogen-free ionic liquids (e.g., benzenesulfonates [13], toluenesulfonates, alkylsulfates [14], hydro-gensulfate [15, 16], dicyanamides [17], thiocyanates [18], etc.), as well as functionalized (task-specific) [19-23], fluorinated [24], deuterated [25] and chiral ionic liquids [26-30]. 

Direct synthesis of sulfur based ionic liquids has been developed as a useful synthetic method for halogen free ionic liquids. The synthesis of sulfur based ionic liquids can generally be split in to two sections (1) sulphonate and (2) sulphate based ionic liquids (Scheme 9). The sulphate based salts are more common than the sulphonates. 

Dong et al. reported the preparation of a novel Brbnsted acid-surfactant-combined halogen-free ionic liquid [DDPA][HSO ] that bears a propane sulfonic acid group in an acyclic dimethyldodecylammonium cation (Fig. 12.69) [42] and its use in the heterogeneous catalysis procedure of one-pot three-component Mannich-type reaction in aqueous media. 

It is interesting to note that all the modified alkyl sulfate ionic liquids obtained with these alcohols show attractively low viscosities and their melting points were all below 0 °C. Thus, this synthesis sequence created a new class of halogen-free ionic liquids with attractive physicochemical properties. No organic solvent is needed in... 

Kondo Y, Koyama T, Tsuboi R, Nakano M, Miyake K, Sasaki S (2013) Tribological performance of halogen-free ionic liquids as lubricants of hard coatings and ceramics. Tribol Lett 51 (2) 243-249. doi 10.1007/sll249-013-0159-l... 

Minami I, Inada T, Okada Y (2012) Tribological properties of halogen-free ionic liquids. Proceedings of the Institution of Mechanical Engineers, Part J. J Eng Tribol 226(111) 891-902. doi 10.1177/1350650112446276... 

Ionic liquid s extraction power for DBT is not uniquely based on chemical interactions involving the acid proton Desulphurization is hardly affected by the chemical nature of the anion. The size of the anion is rather important for the extraction effect Pronounced effect of the cation s size on the extraction power of the ILs. A possible explanation for this behaviour may be that the physical solubility of DBT in the IL is dependant on stearic factors The use of halogen-free ionic liquids avoids stability and corrosion problems. Extraction is only to a small extent influenced by the degree of alkylation of the DBT derivatives, which is a major advantage compared to HDS... 

Figure 7.15 Halogen-free ionic liquids derived from sulfonates.

Itoh, T., Ouchi, N., Hayase, S. Nishimura, Y. (2003). Lipase-Catalyzed Enantioselective Acylation in a Halogen Free Ionic Liquid Solvent System, Chem. Lett, 32, pp. 654-655... 

This table illustrates pretty well that the large-scale ionic liquid will probably not comprise a diallcylimidazolium cation and a [CE3S02)2N] anion. Over a medium-term timescale, we would expect a range of ionic liquids to become commercially available for 25-50 per liter on a ton scale. Halogen-free systems made from cheap anion sources are expected to meet this target first. 

In this context, the use of ionic liquids with halogen-free anions may become more and more popular. In 1998, Andersen et al. published a paper describing the use of some phosphonium tosylates (all with melting points >70 °C) in the rhodium-catalyzed hydroformylation of 1-hexene [13]. More recently, in our laboratories, we found that ionic liquids with halogen-free anions and with much lower melting points could be synthesized and used as solvents in transition metal catalysis. [BMIM][n-CgHi7S04] (mp = 35 °C), for example, could be used as catalyst solvent in the rhodium-catalyzed hydroformylation of 1-octene [14]. 

The author anticipates that the further development of transition metal catalysis in ionic liquids will, to a significant extent, be driven by the availability of new ionic liquids with different anion systems. In particular, cheap, halogen-free systems combining weak coordination to electrophilic metal centers and low viscosity with high stability to hydrolysis are highly desirable. 

TABLE 7.4. Biphasic hydroformylation using halogen-free octylsulfate and tosylate ionic liquids compared with the same reaction in [BMIM][PF6]... 

Although these reactions operate under solvent-free conditions (with an excess of the arene), many Friedel-Crafts acylations utilize volatile and hazardous halogenated solvents. Here, their replacement by ionic liquids can considerably lower the environmental risks and provide a greener chemistry . Ionic liquids with their unique miscibility properties, high thermal stability and miniscule vapor pressure are valuable alternatives for the wide range of traditional solvents available. 

Halogen-free phosphorus based ionic liquids can be produced by direct reaction of (1) phosphines with sulphates (2) tertiary phosphines or imidazoles with alkylating agents such as trialkylphosphates, dialkylphosphonates andmonoalkylphosphinates or (3) phosphines with acid (Scheme 7). 

Scheme 7 Halogen free synthesis of phosphonium ionic liquids...

The advantages of this method, in which a relatively nontoxic (halogen-free) and reusable Bronsted acidic ionic liquid is employed as an effective catalyst, are high catalytic efficiency, short reaction times, high yields, a straightforward work-up, and environmental benignancy. 

Dong and cowoikers have also reported the preparation of some dicationic acidic ionic liquids as halogen-free TSILs that bear dialkane sulfonic acid groups in acyclic diamine cations (Fig. 12.71) [43] and their application as catalysts in a one-pot three-component Biginelli-type reaction (Fig. 12.72). 

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