Catalyst comprising an amidophosphonium salt for halex reactions

Details Catalyst comprising an amidophosphonium salt for halex reactions Catalyst comprising an amidophosphonium salt for halex reactions

1999-07-21

2000-08-15

McKane, Joseph

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Phosphorus or compound containing same

544334, 544409, 546345, B01J 2714, C07D23902, C07D24102, C07D21172

Patent

active

061036595

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The present invention relates to an improved catalyst system for preparing fluorine-containing compounds by means of a halogen-fluorine exchange reaction.
Fluorine-containing compounds are employed, inter alia, in liquid crystal mixtures (EP 0 602 596).
The halogen-fluorine exchange reaction is also known as the halex reaction. It represents a frequently practised method of introducing fluorine substituents into a compound containing halogen which can be replaced by fluorine.
In aromatic compounds, in particular activated aromatic compounds, the halogen-fluorine exchange occurs as a nucleophilic substitution. This reaction requires comparatively high reaction temperatures which are frequently from 200 to 300.degree. C., as a result of which sometimes considerable amounts of decomposition products are formed. In general, it is not possible to work without a solvent, so that the space-time yields are considerable lower than for solvent-free processes. As an alternative to this, it is possible to use conventional phase-transfer catalysts which enable some of the abovementioned disadvantages to be reduced.
Other problems, for example poor stirrability of the reaction suspension in solvent-free processes, still remain. Phase-transfer catalysts which have hitherto been used are quaternary alkylammonium or alkylphosphonium salts (U.S. Pat. No. 4,287,374), pyridinium salts (WO 87/04194), crown ethers or tetraphenylphosphonium salts (J. H. Clark et al., Tetrahedron Letters 28 [1987], pages 111 to 114). Some of these phase-transfer catalysts have a comparatively low activity and are only moderately stable at the temperatures required for carrying out the reaction.
In view of these restrictions and disadvantages, there is a great need for an improved catalyst system by means of which the disadvantages inherent in the known processes, in particular high reaction temperatures and long reaction times, are avoided and in addition, the desired fluorine-containing compounds, in particular nonactivated aromatic compounds too, are obtained in good to very good yield at relatively low reaction temperatures and relatively short reaction times.
It has been found that a mixture of an amidophosphonium salt of the formula (I) with one or more compounds selected from the group consisting of quaternary ammonium salts, quaternary phosphorium salts and polyethers surprisingly fulfils the abovementioned requirements.
The present invention provides a catalyst for halogen-fluorine exchange reactions on aromatics, consisting essentially of a mixture of one or more compounds of the component a) plus at least one compound of the components b), c) and/or d), where the component ##STR2## where A.sup.1, A.sup.2, A.sup.3, A.sup.4, A.sup.5, A.sup.6, A.sup.7, A.sup.8 are, independently of one another, identical or different and are each a straight-chain or branched alkyl or alkenyl having from 1 to 12 carbon atoms, cycloalkyl having from 4 to 8 carbon atoms, an aryl having from 6 to 12 carbon atoms, an aralkyl having from 7 to 12 carbon atoms, or A.sup.1 A.sup.2, A.sup.3 A.sup.4, A.sup.5 A.sup.6, A.sup.7 A.sup.8 are, independently of one another, identical or different and are in each case connected to one another either directly or via O or N--A.sup.9 to form a ring having from 3 to 7 ring atoms, A.sup.9 is an alkyl having from 1 to 4 carbon atoms and B.sup.-- is a monovalent acid anion or the equivalent of a polyvalent acid anion, ##STR3## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are identical or different and are each H.sub.2m O).sub.p R.sup.5, where R.sup.5 is a linear or branched alkyl radical having from 1 to 16, preferably from 1 to 8, carbon atoms or C.sub.1 -C.sub.4 -alkylaryl, in particular benzyl, m is an integer from 1 to 10, preferably from 1 to 5, and p is a number from 1 to 15, preferably from 2 to 10; or to 18, carbon atoms; naphthyl radical, where the substituents are halogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, nitro, CF.sub.3 or cyano; and I.sup.-, Br.sup.-, BF.sub.4.sup.-, 1/2SO.sub.4.sup.2-, C.s

REFERENCES:
patent: 5463148 (1995-10-01), Papenfuhs et al.
patent: 5502235 (1996-03-01), Zettler et al.

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