Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic halides
Reexamination Certificate
1999-07-29
2002-12-03
Killos, Paul J. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic halides
Reexamination Certificate
active
06489510
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the production of carboxylic acid fluorides by photochemical oxidation and to an apparatus therefor.
Polyhalogenated carboxylic acid fluorides are intermediates in chemical synthesis. They can be used, for example, in the production of water-repellant or oil-repellant compounds for use in paper and cloth. They can also be used as a precursor for the production of surface active substances or in flameproofing.
Perfluorocarboxylic acid fluorides can be prepared according to European Patent Application EP-A 260713 by the heat treatment of perfluoroalkyl vinyl ethers in the presence of special salts containing fluorides, such as alkali fluorides, alkaline earth fluorides, fluorometallates, transition metal fluorides or oxyfluorides. A minimum temperature of 250° C. is necessary for the heat treatment. Conversion rates and selectivity are not constant throughout the course of the reaction: initially the conversion rates and the selectivity are low.
International Patent Application WO 96/29298 entitled: “Process for the production of polyfluoracyl preparations” discloses that polyhaloacyl fluorides such as trifluoroacetyl fluoride and difluoroacetyl fluoride can be produced by oxidation of 1-chloro-1,2,2,2-tetrafluoroethane or 1,1-dichloro-2,2-difluoroethane. This is a thermal process which is performed as regards temperature and pressure at or above the critical point. The process is not very selective regarding the formation of carboxylic acid fluoride: in the production of trifluoracyl compounds, trifluoroacetyl fluoride forms in an amount of at least 60 to 70 mole-%, trifluoroacetyl chloride in an amount from 5 to 15 mole-%, trifluoroacetic acid in an amount of 10 to 20 mole-%, 5 to 10 mole-% of a dimerization product (octafluorodichlorobutane), and 1 to 5 mole-% of chlorofluorophosgene.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method whereby carboxylic acid fluorides can be produced in a technical simple manner in a high yield and with a high selectivity. This object is achieved by the method of the invention.
The method of the invention for preparing carboxylic acid fluorides of the general formula RCFXC(O)F comprises the photochemical oxidation of compounds of the general formula RCFXCHFCl as an educt, in which R represents F or linear perfluorinated C1-C9 alkyl or branched, perfluorinated C1-C9 alkyl, and X represents chlorine or fluorine, with oxygen as reactant in the gas phase. The operation is thus carried out with activating irradiation of the gaseous reaction mixture. The irradiation can be carried out through glass of any composition (e.g., through glass within the apparatus, glass enclosures for the irradiator). For example, quartz glass apparatus can be used. The rate of reaction is increased when it is performed in the presence of a sensitizer, especially in the presence of elemental chlorine as sensitizer. Irradiators such as radiation lamps and fluorescent tubes can be used, which emit radiation within a range of 200 to 600 nm, for example. It is advantageous to perform an activating irradiation with light of a wavelength of &lgr;≧280 nm. The invention will be further explained with reference to this preferred embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Conversion rates, yield and selectivity are especially high if the reaction is performed in the presence of elemental chlorine and selects an activating irradiation with light having a wavelength of &lgr;≧280 nm. Frequencies of a wavelength below 280 nm are then substantially masked out of the frequency spectrum. This can be done by using lamps which emit only light of a wavelength above or at 280 nm, and/or by using means which mask out the corresponding frequencies from the emitted light. For example, radiation can be performed through glass which is permeable only for light of a wavelength of 280 nm or above, i.e., glass which filters out the shorter-wavelength content of the radiation. Borosilicate glasses, for example, are well suited for the freqpurpose. Suitable glasses contain, for example, 7 to 13% B
2
O
3
, 70 to 80% SiO
2
, also 2 to 7% Al
2
O
3
and 4 to 8% Na
2
O+K
2
O as well as 0 to 5% alkaline earth metal oxides (all weight-percent). Known brand names for borosilicate glass e s are Duran, Pyrex and Solidex.
Particularly well suited for the irradiation are lamps which emit only (UV) light of a wavelength above or at 280 nm. Especially fluorescent tubes (e.g., those made by Philips) are very well suited. With such lamps the irradiation can be performed through quartz glass, but also through the glasses described above which filter out the shorter wavelength component of the radiation. It is of course necessary that the lamps or tubes emit also in the absorption range of elemental chlorine. In addition to the especially suitable fluorescent tubes, radiation lamps (e.g., medium or high-pressure mercury lamps) can also be used, for example; any lines in the range below 280 nm are filtered out, for example by radiating through a glass which is permeable only to light having a wavelength at or above 280 nm. Usable glasses are described further above. Also well suited for the irradiation are lamps, e.g., mercury high-pressure lamps, which radiate mainly or only in the preferred wavelength range at or above 280 nm on account of a dopant. High-pressure mercury lamps, for example, exhibit a quite intense band in the range of 254 nm, which, as described above, can be filtered out through borosilicate glass, for example. In the case of high-pressure mercury lamps doped with metal iodides, this line is greatly suppressed. The often over-proportional increase of the conversion rate when such doped radiators are used is surprising. Especially well suited are high-pressure mercury lamps which are doped with gallium iodide, especially thallium iodide or cadmium iodide. Even when such doped lamps are used, it is advantageous to filter out the shorter wavelength radiation component with &lgr;<280 nm, for example by working in borosilicate glass.
With regard to reaction temperature and pressure it is possible to conduct the reaction so that no condensation occurs within the photoreactor. If higher boiling educts are used, it can be performed in vacuo, for example. In regard to temperature, the reaction is advantageously carried out at temperatures up to 200° C. The preferred temperature range is 30 to 150° C. As stated, the operation can be performed at reduced pressure; preferably the pressure is at least 1 bar absolute. It is especially preferred to operate at a pressure of 1 to 10 bar (abs.). It is very especially preferred to operate in a pressureless manner. The term, “pressureless,” in the context of the present invention, means that no additional pressure acts upon the reaction mixture except for the ambient pressure (i.e., about 1 bar), the oxygen gas pumping pressure (or that of an oxygen-containing gas, since air or mixtures of oxygen and inert gas, for example, can be used) and the optionally utilized chlorine as well as the pressure that may develop due to hydrogen chloride gas forming in the reaction. The total pressure in the reactor then is advantageously lower than 2 bar absolute or, depending on the pumping pressure, even lower than 1.5 bar absolute, but greater than the ambient pressure.
The process can be performed batch-wise or continuously, in which case the reaction is advantageously carried out in a continuous-flow apparatus. Preferably, one proceeds by continuously feeding starting material (the corresponding educt, oxygen or an oxygen-containing gas, and, optionally chlorine) into the continuous-flow apparatus and continuously withdrawing reaction product in an amount corresponding to the amount fed in.
The molar ratio between the educt and oxygen can vary within a wide range; however, it is desirable to use at least 0.4 mole of oxygen per mole of starting compound. Especially good results are achieved if the molar ratio between the starting compound and the oxygen rang
Braun Max
Eichholz Kerstin
Rudolph Werner
Crowell & Moring LLP
Killos Paul J.
Solvay Fluor und Derivate GmbH
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