Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1998-12-10
2001-04-24
Shah, Mukund J. (Department: 1674)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S129000
Reexamination Certificate
active
06222078
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of making an &agr;-chloro-&agr;,&agr;-difluoro aromatic compound, such as &agr;-chloro-&agr;,&agr;-difluoro-toluene, &agr;,&agr;′-dichloro-&agr;,&agr;,&agr;′,&agr;′-tetrafluoro-p-xylene (DCTFPX), &agr;,&agr;′-dichloro-&agr;,&agr;,&agr;′,&agr;′-tetrafluoro-m-xylene (DCTFMX), &agr;,&agr;′,&agr;″-trichloro-&agr;,&agr;,&agr;′,&agr;′,&agr;,&agr;″-hexafluoro-mesitylene, and &agr;-chloro-&agr;,&agr;-difluoro-naphthalene. In particular, it relates to the reaction of an &agr;,&agr;,&agr;-trichloro aromatic compound with hydrogen fluoride (HF) in the presence of a catalyst to produce the corresponding &agr;-chloro-&agr;,&agr;-difluoro compound.
DCTFPX is a precursor for an inter-layer dielectric material used for making semiconductor chips; it is also a precursor for inert and transparent conformal coatings for electrical components. It has been made by reacting the corresponding dialdehyde with SF
4
followed by side-chain chlorination. See “The Synthesis of 1,1,2,2,9,9,10,10-Octafluoro-[2.2]paracyclophane” by S. W. Chow et al., The Journal of Organic Chemistry, vol. 35, pages 20-22 (1970), “The Chemistry of Sulfur Tetrafluoride. II. The Fluorination of Organic Carbonyl Compounds,” by W. R. Hasek et al.,
J. Amer. Chem. Soc.;
vol. 82, pages 543-551 (1960), and “Synthesis and Chemistry of Several Fluorinated p-Xylenes Designed as Precursors for &agr;,&agr;,&agr;′,&agr;′-Tetrafluoro-p-Xylene,” by S. A. Fuqua et al.,
Tetrahedron,
vol. 20, pages 1625-1632, (1964).
SUMMARY OF THE INVENTION
We have discovered that an &agr;-chloro-&agr;,&agr;-difluoro aromatic compound can be prepared in high yield by reacting the corresponding trichloro compound with hydrogen fluoride in the presence of a particular type of catalyst. For example, DCTFPX and DCTFMX can be prepared by reacting &agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′-hexachloro-p-xylene (HCPX) or &agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′-hexachloro-m-xylene (HCMX), respectively, with HF in the presence of that catalyst.
We have found that under the conditions of this invention, the predominate reaction is that exactly four of the chlorines on the HCPX or HCMX are replaced with fluorines, two from each of the two pendant groups on the benzene ring, rather than three from one group and one from the other group. The reaction proceeds under relatively mild conditions and is easily controlled.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The substrates for the process of this invention have the general formula
where Y is C or N, each R is independently selected from halogen, R′, amino, NHR′, NR′
2
, OR′, OCF
3
, and nitro, R′ is alkyl from C
1
to C
10
, n is 1, 2, or 3, and m is 0 to 5. Preferably, n is 2 and the R groups are all halogen as the products made from those substrates are commercially more important; m is preferably 0 when n is 2. If n is 2, the two trichloromethyl groups are preferably meta or para. Examples of such substrates include benzotrichloride (BTC), HCPX, HCMX, and &agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′,&agr;,&agr;,&agr;″-nonachloromesitylene. HCPX and HCMX are the most important substrates. HCPX has the following structure:
When it is reacted with HF, DCTFPX is produced:
While some tri and penta fluorinated products are present at the end of the reaction, unexpectedly, very little of the following two products are made:
Some of the substrates are commercially available. HCMX and HCPX can be made by reacting m-xylene or p-xylene, respectively, with chlorine free radicals in a solvent. See U.S. patent application Ser. No. 09/208,676, filed of even date, titled, “Method of Making &agr;-Chloroxylenes,” herein incorporated by reference, which discloses the chlorination of xylenes. In that patent application, the chlorine free radicals are generated in situ using ultraviolet light or a chlorine free-radical initiator, such as &agr;,&agr;′-azobisisobutynitrile (AIBN) or &agr;,&agr;′-azobis(cyclohexanecarbonitrile) (sold by Dupont as “VAZO-88”). The reaction temperature can be about 70 to about 160° C., but the best results were obtained at about 80 to about 90° C. Heating at reflux is also preferred as that reduces ring chlorination. The preferred solvents are toluene, ring halo subtituted toluene, benzotrifluoride (BTF) and &agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′-hexafluoroparaxylene (HFPX) or &agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′-hexafluorometaxylene (HFMX), but other solvents can also be used. No base is added to the reaction. At the end of the reaction, a mixture of HCPX or HCMX and the solvent is recovered. The solvent used in the chlorination reaction can be used in the fluorination reaction without separating it, which eliminates processing steps.
The substrate can be melted and reacted with HF gas in the absence of a solvent. The reactor is preferably heated above the melting point of the substrate, e.g., to about 115 to about 120° C. for HCPX. The substrate is placed in the reactor, the catalyst is added, the reactor is closed and heated, and HF gas is admitted to so the reactor. The HF gas can be added even if the substrate is not yet fully melted. As the reaction proceeds, the temperature can be gradually reduced to about 40 to about 85° C., but preferably to about 50 to about 70° C. At lower temperatures more overfluorinated products are formed, reducing the yield of dichlorotetrafluoro product, and at higher temperatures HF efficiency is poor. The reaction can be followed by gas chromatography (GC) to determine when the yield of the dichlorotetrafluoro product is maximized.
It is preferable to use a solvent because a solvent reduces the build up of solids in the reactor condenser. Any organic solvent that is inert in this reaction (including solvents that fluorinate to an inert solvent, such as benzotrichloride, BTC), dissolves the substrate, or forms a slurry with the substrate and boils at a temperature higher than about 70° C. is suitable. Examples of such solvents include BTC, BTF, ring halo substituted BTC and BTF, such as orthochlorobenzotrifluoride (OCBTF), metachlorobenzotrifluoride (MCBTF), parachlorobenzotrifluoride (PCBTF), and 3,4-dichlorobenzotrifluoride (3,4-DCBTF), HFPX, HFMX, toluene, xylenes, mesitylenes, and ring halo substituted toluene, xylenes, mesitylenes, and mixtures thereof; BTF, HFPX, and HFMX are preferred. Low boiling products, such as chloropentafluoroxylenes, dichlorotetrafluoroxylenes, trichlorotrifluoroxylenes, tetrachlorodifluoroxylenes, and mixtures thereof can also be used as solvents. If a solvent is used, the substrate can be added as a powdered solid to the solvent, or added in solution. A solution is preferred as this simplifies operations and the reaction will occur at a lower temperature, which reduces the amount of HF and organics that are condensed. Other advantages to using a solvent include better HF efficiency, increased throughput, less environmental cleanup since very little organic and HF reach the scrubber solution, and problems associated with solids, such as plugging in the condenser and pipes and variations in the temperature of the reactor, are avoided. The percent solids in the solution can be about 10 wt % to about 95 wt %; a lower percent solids is not beneficial due to lower reactor throughput or a slower rate of reaction; preferably, the percent solids is about 30 to about 80. If a solvent is present, the reaction can be started at about 60 to about 105° C., then lowered to about 40 to about 85° C., but preferably to about 50 to about 70° C., after about one equivalent of HF has been added.
About 0.7 to about 1.4 equivalents of HF are used per equivalent of chlorine to be substituted. If less than 0.7 equivalents of HF are used, the product yield falls and more than 1.4 equivalents is unnecessary. It is preferable to use about 0.9 to about 1.25 equivalents of HF per equivalent o
Benson Kevin R.
Franc James
Mandal Sanjay
Brookes Anne E.
Fuerle Richard D.
Occidental Chemical Corporation
Rao Deepak R.
Shah Mukund J.
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