Patent Application
20060211871
This invention relates to new synthetic routes to the preparation of hydrophobic ionic liquids and the ionic compounds made thereby.
Ionic liquids are organic salts with melting points below 100° C. and typically are liquids at room temperature. Early interest in the compounds was based upon their conductivity, as described in U.S. Pat. No. 4,764,440. Ionic liquids may be used as a solvent in a chemical vapor deposition system (U.S. Published Patent Application No. 2002/0001674), as coupler solvents in photothermographic systems (U.S. Pat. No. 6,531,270), as solvents for Friedel-Crafts and Diels-Alder reactions (U.S. Pat. No. 6,573,405), as a catalyst for isomerisation reactions, (U.S. Published Patent Application No. 2003/0109767), as complexing agents in separations (U.S. Published Patent Application No. 2003/0125599 and U.S. Pat. No. 6,623,659) as a solvent to form regenerated cellulose (U.S. Published Patent Application No. 2003/0157351), and as a polymerization catalyst (WO 03/087390), to name a few.
Ionic liquids may be made by the reaction of an onium chloride with a Lewis acid such as AlCl3. Heterocyclic halides react with lithium borates in acetonitrile to form ionic liquids useful in electrochemical cells (U.S. Published Patent Application No. 2002/0015883) and with lithium trifluorophosphates to form inert solvents (U.S. Published Patent Application No. 2002/0015884). EMICI (1-methyl-3-ethyl imidazolium chloride) may be reacted with potassium bis-fluorosulfonimide (KFSI) to yield a conductive liquid useful as a current collector (U.S. Pat. No. 6,365,301). Sulfonated or carboxylated triesters of phosphorous acid may serve as anions for ammonium cations (U.S. Published Patent Application 2002/0161261). Salts of diazonium, sulfonium, iodonium or metallocennium types may be useful in chiral syntheses (U.S. Pat. No. 6,548,567).
An aqueous nitrate of Ag(I) may be reacted with an imidazolium chloride to form an ionic liquid and a silver chloride salt (U.S. Pat. No. 6,379,634). A halide-free ionic liquid may be obtained by reacting a halide salt of an organic cation with a Br{acute over (ø)}nsted acid in an alcohol or hydrocarbon solvent (WO 03/051874).
A two-step continuous process is disclosed in WO 03/089389. WO 03/093246 describes liquids wherein the cation is a nitrogen or phosphorous compound and the anion is a five-member nitrogen heterocycle. A process to minimize halides in ionic liquids is based on fluorinated esters or alkyl sulfonates as replacements for haloalkanes when forming an imidazolium salt (U.S. Published Patent Application No. 2003/0080312) and lower melting temperatures have been obtained when the cation is Zn, Sn or Fe (III) and the anion is a quaternary amine (U.S. Pat. No. 6,573,405).
Chiral ionic liquids may be made from optically active ammonium cations and used for asymmetric syntheses (U.S. Published Patent Application No. 2003/0149264). Metallic cations and perhalogenated substituents on the anionic portion are disclosed in U.S. Pat. No. 6,620,546.
In consideration of the many uses for ionic liquids, a need exists for liquids with different properties with new uses and for new ways to make them.
The invention relates to new methods for the synthesis of ionic compounds, especially liquids, and to the new liquids made by the methods. These liquids are salts that are liquid at room temperature, hence RTIL. The liquids are hydrophobic and compatible with extraction processes and reaction schemes in organic chemistry.
The objectives of this invention may be met using the complexation of cations by neutral liqands. This produces room temperature ionic liquids having cationic coordination metal complexes.
Crown ethers are readily available commercially and used primarily in chemical research because the exposed oxygen atoms readily complex with metal ions. Depending on substituents, the crown ethers may have adjustable solubility in aqueous solvents.
When reacted with an alkaline organic salt, crown ethers form coordination metal complexes of the ether and the alkaline metal, together with an organic anion gegenion. The organic salt of many of these compounds is a room temperature ionic liquid with a low volatility and is strongly hydrophobic.
Suitable crown ethers for this purpose are shown in
Suitable metals are sodium, potassium, lithium and calcium
These reactions are exothermic and require no solvent, heat or catalyst. Excess reagent salt can be washed away.
A similar system may be formed using small cations with neutral organic ligands in what formally appear to be a methathesis reactions, an exchange of anions. Organic amines are representative of the neutral liqand. Silver is a representative small cation and forms stable complexes with amines. Salts such as lithium bis(trifluoromethane)sulfonimide are suitable for exchange because they supply a suitable bulky anion. Such systems are readily worked-up using water to remove salt residues.
Table 1 shows representative examples of alkyl amine salts, yields and properties.
Suitable metal ions include Ag+1, Zn2+, Cu2+, Cd2+, Ni2+, Hg2+, and Fe3+.
The structural features of the cations of these ionic liquids are given in
Other neutral liqands for purposes of this invention include sulfur and phosphorous compounds containing neutral liqands.
Neat cyclohexyl-15-crown-5 (Parish, Inc.), was mixed with an equimolar amount of N-lithiobis(trifluoromethane)sulfonimide Li(Tf)2N in a boiling flask at room temperature without an inert blanket and stirred using a magnetic stir bar. Warming was apparent tactilly and a clear colorless solution obtained.
The same compounds under the same conditions were reacted at a ratio of cyclopexo-15 crown-5 to Li(Tf)2N of 1:1.35.
No loss of mass was observed during vacuum rotary evaporation at 100° C. for four hours.
Both products were soluble in organic solvents including acetone and acetonitrile but immiscible in water and aqueous solutions.
Compounds according to Table 1 were obtained by mixing amines of the formula R1, R2—NH2 with 1:1 aqueous solution of AgNO3 in D.I. water at room temperature with stirring. A stoichometric amount, based upon amount of R—NH2 of Li(Tf)2N was added to a stirred solution of the Ag (H2NR,) (H2NR2)obtained from the first step was added with stirring and the mixture was stirred for one hour and then poured into a separatory funnel. The lower layer of water containing dissolved LiNO3 was drawn off. The RTIL obtained was washed three times with D.I. water and dried using a vacuum rotary evaporator at 80° C. for six hours. The dried product was weighed and the yield calculated based upon Ag.
Table lists the various R-groups used, the yield, density and conductivities measured using a conductivity meter.
Draft
It is noted that in all cases the shifts, splits and integrations shown in the figures are consistent and predictable for the structures.
The RTIL of this invention are unique because they are the first such liquids having an inorganic cation complexed with a neutral organic liqand. They have conductivities comparable to the traditional EMI+ salts but are formed by different processes allowing a greater tuning by changing substituents on the organic liqand. These compounds are believed to be useful cosolvents in the separation of metal salts from contaminated aqueous systems, especially systems contaminated with soluble radioactive compounds such as those with strontium slats. They are also useful in the separation of alliances from olefins, with particular application to propane: propylene system. This invention has been described in terms of representative examples. Modifications and additions obvious to those with skills in the art are subsumed within the scope of the invention. H2N—R2)Tf2N−ionic liquids.
aThe corresponding salts are solid at room temperature.
A similar system may be formed using small cations with neutral organic ligands in what formally appear to be a methathesis reactions, an exchange of anions. Organic amines are representative of the neutral liqand. Silver is a representative small cation and forms stable complexes with amines. Salts such as lithium bis(trifluoromethane)sulfonimide [(CF3SO2)2N—Li, “lithiotrifluorosulfonylamide, Li (Tf2)N], BF4−, NO3−, SO4−, PO4+3, PF6− and dicyanamide [N(CN)2−] are suitable for exchange because they supply a suitable bulky anion. Such systems are readily worked-up using water to remove salt residues.
Suitable metal ions include Ag+1, Zn2+, Cu2+, Cd2+, Ni2+, Hg2+, Co3+ ions and Fe3+.
The same compounds under the same conditions were reacted at a ratio of cyclohexyl-15-crown-5 to Li(Tf)2N of 1:1.35.
The RTIL of this invention are unique because they are the first such liquids having an inorganic cation complexed with a neutral organic liqand. They have conductivities comparable to the traditional EMI+ salts but are formed by different processes allowing a greater tuning by changing substituents on the organic liqand. These compounds are believed to be useful co-solvents in the separation of metal salts from contaminated aqueous systems, especially systems contaminated with soluble radioactive compounds such as those with strontium1, cesium, silver, copper and lanthanum salts. They are also useful in the separation of alkanes from olefins, with particular application to propane: propylene system. This may be useful as liquid separation membrane for gasses, as sensing transducers, electrolyte for super capacitors, as stationary phases for chromatography and as heat transfer fluids. This invention has been described in terms of representative examples. Modifications and additions obvious to those with skills in the art are subsumed within the scope of the invention.
This invention was made with United States Government support under Contract No. DE-AC05-960R 22725 between the United States Department of Energy and Oak Ridge National Laboratory, managed by UT-Battelle, LLC, and the United States Government has certain rights in this invention.
