Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1998-02-10
2001-04-10
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C502S162000, C502S164000
Reexamination Certificate
active
06215032
ABSTRACT:
TECHNICAL FIELD
This invention relates to halogen exchange reactions involving haloaromatic compounds and alkali metal fluorides, and more particularly to processes for recovering valuable catalyst components for reuse particularly, but not necessarily, in halogen exchange reactions.
BACKGROUND
Halogen exchange reactions for fluorinating haloaromatic compounds using alkali metal fluorides as the fluorine source have been extensively studied heretofore. Typically they involve the reaction of a chloroaromatic compound with potassium fluoride, rubidium fluoride or cesium fluoride by heating the reactants to extremely high temperatures (above about 400° C.) in the absence of an ancillary diluent or solvent, or by conducting the reaction at temperatures of around 200-230° C. in an aprotic solvent such as sulfolane. It has also been reported that organic fluorine compounds such as pentafluorobenzonitrile, tetrafluorophthalonitriles and pentafluoropyridine can be formed by reacting a corresponding chloro- or bromo-substituted compound with alkali metal halide such as potassium fluoride in benzonitrile as solvent at 190° C. to 400° C. in a sealed autoclave under autogenous pressure.
Use of catalysts in some exchange reactions has also been studied. Such catalysts have included quaternary ammonium salts, metal carbonyls, crown ethers and cryptates. In now commonly-owned application Ser. No. 08/754,338, filed Nov. 22, 1996, now U.S. Pat. No. 5,824,827, all disclosure of which is incorporated herein by reference, Igor Bildinov et al. describe a significant improvement in halogen exchange technology, namely that aminophosphonium compounds such as one or more tetra(dihydrocarbylamino)phosphonium halides are highly effective catalysts for halogen exchange reactions whether the reaction is conducted as a mixture of solids or as a slurry.
Aminophosphonium catalysts, such as tetra(dihydrocarbylamino)phosphonium halides, although highly effective as catalysts, are nonetheless relatively expensive materials. Thus it would be highly desirable to recover such catalysts for reuse as catalysts. However, the formation of heavy ends during halogen exchange reactions complicates the recovery of such catalyst components in suitably pure, catalytically active form. Thus a need has existed for an effective way of recovering such catalysts in catalytically active form enabling reuse of such materials, especially as halogen exchange catalysts. This invention is deemed to fulfill this need most expeditiously.
BRIEF SUMMARY OF THE INVENTION
The halogen exchange reactions with which this invention is concerned typically involve heating a mixture formed from ingredients comprising (A) at least one finely-divided alkali metal fluoride, (B) at least one haloaromatic compound having at least one halogen atom of atomic number greater than 9 on an aromatic ring, (C) an aminophosphonium catalyst, and (D) at least one liquid aprotic solvent/diluent at one or more reaction temperatures at which at least one halogen atom of the haloaromatic compound is replaced by a fluorine atom.
In one of its most basic embodiments this invention involves the discovery that it is possible to separate catalytically-active aminophosphonium catalysts from mixtures composed predominately of aminophosphonium catalyst residue(s) and heavy ends from a halogen exchange reaction conducted in an aprotic solvent/diluent. To accomplish this, such mixtures are extracted with a neutral or acidic aqueous extraction solvent medium.
In another of its embodiments this invention provides a process for recovering aminophosphonium catalyst from a halogen exchange reaction mixture in which the reaction was performed using an aminophosphonium catalyst in a liquid aprotic solvent/diluent and in which at least one fluoroaromatic compound was produced and heavy ends were co-produced, which process comprises (i) isolating a liquid mixture composed predominately of aminophosphonium catalyst residue(s) and heavy ends, and (ii) extracting at least a portion of the mixture from (i) with a neutral or acidic aqueous extraction solvent medium to separate aminophosphonium catalyst therefrom.
As regards step (i) above, the liquid mixture composed predominately of aminophosphonium catalyst residue(s) and heavy ends can be isolated in various ways. If volatile materials are not completely withdrawn from the reaction vessel during the reaction, the halogen exchange reaction mixture on completion of the reaction and when at room temperature typically comprises (a) a product which comprises at least one fluorinated aromatic compound, (b) aprotic solvent/diluent, (c) alkali metal halide solids, (d) aminophosphonium catalyst residue(s), and (e) heavy ends. To effect the isolation per step (i) above, at least a portion of the product and at least a portion of the solvent/diluent can be recovered from the reaction vessel and/or reaction mixture by distillation and, if desired, can be separated from each other either during the distillation or by means of a subsequent separation, such as distillation or solvent extraction. The solids can be removed by filtration, centrifugation, or other suitable physical solids-liquid separation procedure, in most cases centrifugation being the preferred method. While the distillation and solids removal can be conducted in any sequence, it is preferred to conduct the solids removal prior to distillation. When these operations have been completed the liquid mixture composed predominately of aminophosphonium catalyst residue(s) and heavy ends remains, usually in the form of an oily residue, and this material is then subjected to extraction step (ii) above.
For conducting the extraction pursuant to this invention, the preferred aqueous extraction media are dilute aqueous hydrochloric acid and dilute aqueous hydrobromic acid. The resulting neutral or acidic aqueous solution of the catalyst which is formed in this process can be heated to remove the water and acid, and thereby provide the catalyst in isolated form. Alternatively, the aqueous solution of the catalyst can be extracted with an organic solvent, preferably an aprotic solvent in which water is substantially insoluble, to provide an organic solution of the catalyst. When the aminophosphonium catalyst is to be recycled in a halogen exchange reaction it is preferable to extract the catalyst from the neutral or acidic aqueous solution of catalyst with a low-boiling organic solvent such as methylene chloride, and then conduct a solvent exchange in which the low-boiling organic solvent is replaced by a higher boiling aprotic solvent such as benzonitrile or nitrobenzene to thereby form a solution of the catalyst in the aprotic solvent. This last mentioned solution is ideally suited for recycle to the halogen exchange reaction.
The use of an aqueous extraction medium makes it possible to separate the aminophosphonium catalyst from both heavy ends and other impurities associated therewith, such as most, if not substantially all, of the residual aprotic solvent entrained in the heavy ends, and at least a portion of catalyst decomposition products such as KPF
6
and (NPF
2
)
3
which are typically contained in the heavy ends. Moreover, the aminophosphonium catalyst can be recovered in suitably purified, catalytically-active form from the neutral or acidic aqueous solution formed in the extraction by use of procedures described herein. Impurities, if any, associated with the recovered aminophosphonium catalyst do not materially detract from the effectiveness of the catalyst when recycled to the same or a subsequent halogen exchange reaction. And in addition, catalyst losses incurred during the catalyst recovery operations when properly conducted pursuant to this invention are well within acceptable limits.
These and other embodiments and features of the invention will become still further apparent from the ensuing description and appended claims.
FURTHER DETAILED DESCRIPTION
Halogen Exchange Reactions
Any aromatic compound that has at least one replaceable halogen atom other than fluorine on the arom
Balhoff John F.
Cheng Chi Hung
Lin Ronny W.
Albemarle Corporation
Pippenger Philip M.
Siegel Alan
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