Method for producing bis(trifluoromethyl)imido salts

The present invention relates to novel processes for the preparation of bis(trifluoromethyl)imido salts of the general formula (I):

M a+ [(N(CF 3 ) 2 ) − ] a   (I)

The chemistry of the bis(trifluoromethyl)imido anion is generally based on the chemical reaction of perfluoro(2-azapropene), CF 3 N═CF 2 , as starting material (H. G. Ang and Y. C. Syn, Advances in Inorganic Chemistry and Radiochemistry, Vol. 16 (1974), pp. 1-64; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8 th Edition, Springer Verlag: Berlin, Heidelberg, New York (1991), Part 9, pp. 125-153; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8 th Edition, Springer Verlag: Berlin, Heidelberg, New York (1991), Suppl. Vol. 6, pp. 196-214). This compound can be prepared by fluorination of CCl 3 N═CCl 2 using NaF in sulfolane at 105° C. in a yield of 78% (E. Klauke, H. Holtschmidt, K. Findeisen, Farbenfabriken Bayer AG, DE-A1-2101107 (1971/1972)) or by photolysis of CF 3 N—(CF 2 CFCl 2 )Cl (G. Sawar, R. L. Kirchmeier and J. M. Shreeve, Inorg. Chem. 28 (1989, pp. 2187-2189)) in gas at room temperature (boiling point −33° C.), with special industrial apparatuses being necessary for the said compound.

Di[bis(trifluoromethyl)imido]mercury, Hg[N(CF 3 ) 2 ] 2 , which is very reactive, was synthesised for the first time by Young and his co-workers (J. A. Young, S. N. Tsoukalas and R. D. Dresdner, J. Am. Chem. Soc. 80 (1958), pp. 3604-3606). This compound is a good reagent for the introduction of N(CF 3 ) 2 groups into organic molecules (H. G. Ang and Y. C. Syn, see above; A. Haas, Gmelin Handbook of Inorganic Chemistry, 8 th edition, Springer Verlag: Berlin, Heidelberg, New York (1981), Part 9, pp. 45-46), but is not a very stable compound since it is extremely sensitive to moisture. The synthesis of Hg[N(CF 3 ) 2 ] 2 is difficult, time-consuming and requires special industrial apparatuses and expensive starting materials.

Caesium bis(trifluoromethyl)imide, [Cs] + [N(CF 3 ) 2 ] − , is a further option for the synthesis of bis(trifluoromethyl)amino compounds. This salt is prepared by simply passing perfluoro(2-azapropene) into a solution of caesium fluoride in dry acetonitrile (A. F. Gontar, E. G. Bykovskaja and I. L. Knunyants, IZV. Akad. Nauk SSSR, Otd. Khim, Nauk (1975), pp. 2279-2282).

The disadvantage of this method consists in the formation of a dimeric product through the reaction of the starting material perfluoro(2-azapropene) with the caesium salt that has already formed. This reaction is unavoidable and results in the formation of complex product mixtures.

However, N(CF 3 ) 2 anions are readily accessible through the reaction of some metal fluorides with N,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides [“N(CF 3 ) 2 anion preparation, and its use”, EP 99 101 982]. This process enables the generation of Na, K, Rb, Cs, Ag, Cu(II) and Hg(II) salts with N(CF 3 ) 2 anions. However, the analogous reaction of N,N-bis(trifluoromethyl)perfluoroalkanesulfonamides or -acylamides with other metal fluorides (for example ZnF 2 and CdF 2 ) progresses only very slowly due to the poor solubility of these fluorides in organic solvents.

FIG. 1 is a graphical depiction of the electrochemical stability of an exemplary embodiment of the invention.

FIG. 2 is a graphical depiction of the conductivity of an exemplary embodiment of the present invention.

FIG. 3 is a graphical depiction of the conductivity of a comparative example.

The object of the present invention was therefore to provide an improved process for the preparation of bis(trifluoromethyl)imido salts.

The object according to the invention is achieved by a process for the preparation of bis(trifluoromethyl)imido salts of the general formula (I)

[M a+ ][(N(CF 3 ) 2 ) − ] a   (I)

in which

M a+ is a monovalent or divalent cation, and a=1 or 2,

characterised in that at least one trifluoromethanesulfonate of the general formula (II)

[M a+ ][(OSO 2 CF 3 ) − ] a   (II)

in which

M a+ is a monovalent or divalent cation, and a=1 or 2,

is reacted with bis(trifluoromethyl)imidorubidium in solution, and the resultant bis(trifluoromethyl)imido salt of the general formula (I) is, if desired, purified and/or isolated by conventional methods.

Preference is given to processes according to the invention in which M a+ is a sodium, potassium, caesium, copper or silver cation, and a=1.

Particular preference is given to processes according to the invention in which M a+ is a mercury, copper, zinc or cadmium cation, and a=2.

Particular preference is also given to processes according to the invention in which a=1 and M a+ is a cation of the general formula (III)

[([R b 1 R c 2 R d 3 R e 4 ]A x ) y Kt] +   (III)

in which

Kt═N, P, As, Sb, S or Se, A═N, P, P(O), O, S, S(O), SO 2 , As, As(O), Sb or Sb(O), R 1 , R 2 , R 3 and R 4 are identical or different and are H, halogen, substituted and/or unsubstituted alkyl C n H 2n+1 , substituted and/or unsubstituted C 1-18 -alkenyl having one or more double bonds, substituted and/or unsubstituted C 1-18 -alkynyl having one or more triple bonds, substituted and/or unsubstituted cycloalkyl C m H 2m−1 , monosubstituted, polysubstituted and/or unsubstituted phenyl, substituted and/or unsubstituted heteroaryl;

where

n=1-18, m=3-7, x=0 or 1, y=1-4, y=1 for x=0,

where

b, c, d and e are each=0 or 1, where b+c+d+e≠0, A may be included in various positions in R 1 , R 2 , R 3 and/or R 4 , Kt may be included in a cyclic or heterocyclic ring, the groups bonded to Kt may be identical or different.

The processes according to the invention also enable the preparation of novel bis(trifluoromethyl)imido salts which are difficult to access, such as, for example, cadmium, zinc or copper(I) N(CF 3 ) 2 salts. Novel salts therefore represent a further subject-matter of the present invention.

The salts prepared in accordance with the invention can be used alone or in mixtures with other salts as conductive salts or additives in electrolytes. Besides the salt or salt mixtures, the electrolytes also comprise solvents or solvent mixtures.

These electrolytes are employed in electrochemical cells (such as, for example, primary and secondary batteries). They are preferably employed in capacitors and supercapacitors.

The starting materials bis(trifluoromethyl)imidorubidium and the trifluoromethanesulfonate salts are both readily soluble in a number of organic solvents. In addition, metal triflates are commercially available from a number of companies.

The reaction of Rb[N(CF 3 ) 2 ] and metal triflates at room temperature or below takes place rapidly, for example in accordance with the following general reaction scheme:

x Rb[N(CF 3 ) 2 ]+M(OSO 2 CF 3 ) x →M[N(CF 3 ) 2 ] x +x Rb(OSO 2 CF 3 )

In the process according to the invention, the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) is preferably carried out at a temperature of from −60 to +60° C., particularly preferably from −50 to +50° C., very particularly preferably at from −45 to +30° C.

Preferred solvents for the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) are organic solvents, particularly preferably polar organic solvents.

Very particularly preferred solvents for the conversion to a bis(trifluoromethyl)imido salt of the general formula (I) are the solvents acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile or a mixture of acetonitrile, benzonitrile, dimethoxyethane and/or propionitrile.

Preferred solvents according to the invention comprise ≦0.1% by weight of water, preferably ≦0.01% by weight of water, particularly preferably ≦0.005% by weight of water.

In the preferred processes according to the invention, the trifluoromethanesulfonate salt of the general formula (II) or the bis(trifluoromethyl)imidorubidium is employed in a molar excess of ≦3% or particularly preferably in equimolar amounts.

The rubidium triflate formed by the process according to the invention has limited solubility in organic solvents and can be separated off from the reaction mixture as a solid at low temperatures.

Preferred processes according to the invention are therefore those in which the bis(trifluoromethyl)imido salt of the general formula (I) is purified by filtration at a temperature of from −90 to +30° C., particularly preferably at from −70 to +20° C., after removal of the solvent.

Further purification of a bis(trifluoromethyl)imido salt of the general formula (I) is possible by extraction with dichloromethane and/or hexane and/or diethyl ether. Extraction with dichloromethane is a preferred variant of the present invention.

The invention is explained below with reference to examples. These examples serve merely to explain the invention and do not restrict the general inventive idea.