Method of producing fluorinated compounds

Details Method of producing fluorinated compounds Method of producing fluorinated compounds

1999-03-10

2001-03-20

Wong, Edna (Department: 1741)

Chemistry: electrical and wave energy

Processes and products

Processes of treating materials by wave energy

C204S158110, C204S158120

Reexamination Certificate

active

06203671

ABSTRACT:

FIELD OF INVENTION
The invention relates generally to a process for preparing fluorinated compounds. More specifically, the present invention relates to fluorination using elemental fluorine to produce a hydrofluoroalkane or hydrochlorofluoroalkane, while minimizing formation of perhaloalkane by-products.
BACKGROUND OF THE INVENTION
The commercial potential for highly-fluorinated hydrofluorocarbons (HFCs), such as, 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), continues to be realized. For example, HFC-227ea has been found to be useful semiconductor etchant gas. Accordingly, there is a need for commercially-viable processes of preparing these compounds.
Traditionally, these compounds have been produced using various fluorination processes depending upon the availability of the starting materials and the desired fluorinated product. One common approach, which is of particular interest herein, is fluorination using elemental fluorine. Elemental fluorination typically involves a thermally-catalyzed reaction of elemental fluorine with a hydrofluorocarbon (HFC) or a hydrochlorofluorocarbon (HCFC), in the vapor-phase. The production of such compounds using elemental fluorination, however, is hampered by the formation of perhalogenated by-products such as tetrafluoromethane and octafluoropropane.
In addition to consuming valuable starting materials, the formation of perhalogenated by-products presents environmental problems. More specifically, the atmospheric lifetime of perhalogenated compounds tends to be relatively long thereby contributing to global warming. Both in the United States and abroad, there is a concerted effort underway to limit the production of such compounds.
Therefore, there is a need to develop alternative processes for preparing hydrogen-containing, highly-fluorinated compounds while avoiding the generation of perhalogenated by-products. The present invention fulfills this need among others.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention overcomes the problems of conventional elemental fluorination by using actinic radiation as a photoinitiator in a liquid-phase reaction where the substrate to be fluorinated also serves as the solvent. The reaction produces hydrofluoroalkanes or hydrochlorofluoroalkanes with little or no formation of perhalogenated by-products. Thus, the present invention provides a viable alternative to vapor-phase, thermal fluorination.
One aspect of the invention is the provision of a process for producing a fluorinated product such as a hydrofluoroalkane or hydrochlorofluoroalkane using liquid-phase fluorination catalyzed by actinic radiation. In a preferred embodiment, the process comprises: (a) reacting a molar excess of an aliphatic substrate or starting material in liquid phase with fluorine in the presence of actinic radiation to produce a product mixture containing a fluorinated product; and (b) recovering said product from said fluorinated product mixture.
Preferred aliphatic starting materials include those having the formula:
X—R—Y  (1)
wherein:
R is an unsubstituted or substituted C
1
-C
10
divalent alkyl group having two or more hydrogen atoms; and
X and Y are independently selected from R
h
, F, or Cl, wherein R
h
, is a C
1
-C
10
perhalogenated alkyl.
R may be substituted with, for example, halides, C
1
-C
5
haloalkyls, haloalicyclics, haloaryls substituted haloaryls, nitros, tri-substituted aminos, amidos, cyanos, and haloalkoxys. Preferably, R is an unsubstituted C
1
-C
4
divalent alkyl, for example, methylene (—CH
2
—) and its homologs, such as, —CH
2
CH
2
—, and —CH
2
CH
2
CH
2
—. More preferably, R is methylene.
Preferably, R
h
is a C
1
-C
5
alkyl perhalogenated with chlorine, fluorine or a combination thereof More preferably, R
h
is a perfluorinated C
1
-C
3
alkyl.
Particularly preferred compounds of Formula 1 include the following groups: Group One wherein R is methylene and X and Y are perfluorinated alkyls or X is a perfluorinated alkyl and Y is F, such as, for example, 1,1,1,3,3,3-hexafluoropropane (HFC-236fa), 1,1,1,2,2,4,4,4-octafluorobutane (HFC-338), and 1,1,1,2,2,3,3,4,4,5,-decafluoropentane (HFC-43(10)); and Group Two wherein R is methylene and X is a perhalogenated alkyl and Y is either Cl or F such that Formula 1 contains at least one chlorine, such as, for example, 1,1,1-trifluoro-2-chloroethane (HCFC-133a), 1,1,2-trifluoro-1-chloroethane (HCFC-133b) and 1,1,3-trichloro-1,3,3-trifluoropropane (HCFC-233). In a more preferred embodiment, the starting material belongs to Group One. The most preferred starting material is HFC-236fa. The starting materials described above are preferable because they tend to be commercially available and/or readily synthesized.
It is worthwhile noting that a fluorination reaction may be conducted with a starting material which is not covered by Formula 1, but which eventually becomes fluorinated to the extent that it is covered by Formula 1. In other words, as the reaction proceeds to the production of the fluorinated product, an intermediate along the way may be covered by Formula 1. For example, a compound having a terminal group such as methyl, which is not covered by Formula 1, may be fluorinated in the reaction such that its terminal group becomes fluorinated and thus covered by Formula 1. Therefore, it should be understood that the term “starting material” is not limited to the material initially fed to the reactor, but also covers intermediates that may be produced in the course of fluorination.
The fluorinated product is, of course, a more fluorinated version of the starting material. Thus, a starting material of Formula 1 will produce a fluorinated product having the formula:
X—R′—Y  (2)
wherein:
R′ is R having at least one hydrogen replaced by fluorine and at least one hydrogen remaining; and
X and Y are the same as described above.
As with the starting material, particularly preferred compounds of Formula 2 include the following groups: Group One wherein R′ is fluoromethylene and X and Y are perfluorinated alkyls or X is perfluorinated and Y is F, such as, for example, 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), 1,1,1,2,2,3,4,4,4-nonafluorobutane (HFC-329), and 1,1,1,2,2,3,3,4,4,5,5,-undecafluoropentane (HFC-42(11)); and Group Two wherein R′ is fluoromethylene and X is perhalogenated alkyl and Y is either Cl or F, such that Formula 2 contains at least one chlorine, such as, for example, 1,1,1,2-tetrafluoro-2-chloroethane (HCFC- 124a), 1,1,2,2,-tetrafluoro-1-chloroethane (HCFC-124) and 1,1,3-trichloro-1,2,3,3-tetrafluoropropane (HCFC-224). In a preferred embodiment, the hydrofluoroalkane product belongs to Group One. The most preferred product is HFC-227ea.
In preparing the fluorinated product, the reactants, which include the starting material in liquid phase and elemental fluorine, are contacted in a reactor in the presence of actinic radiation. For purposes of this invention, “actinic radiation” refers to light energy of the required wavelength, intensity and duration to catalyze, or initiate, fluorination. Preferably, the actinic radiation is ultra-violet (UV) radiation. The UV radiation has a wavelength preferably from about 200 to about 400 nm, more preferably from about 250 to about 350 nm, and still more preferably from about 275 to about 300 nm. The ultraviolet light preferably is introduced to the reaction mixture using techniques and apparatus known in the art, such as, for example, irradiating the reaction mixture through a suitably-UV-transparent window (for example, commercially-available quartz or crystalline calcium fluoride or barium fluoride), or circulating the gas-liquid mixture through a suitably-UV-transparent container in close proximity to a UV light source.
During photofluorination, a molar excess of starting material relative to fluorine should be present such that the starting material also acts as a reaction solvent for the elemental fluorine. Using the starting material as a reaction solvent has been found to improve the selectivity of the fluorinated product, thereby d

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