Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
1999-05-19
2001-01-16
Gorgos, Kathryn (Department: 1741)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
Reexamination Certificate
active
06174415
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of chlorinating the side chains of toluene, xylenes, or mesitylenes. In particular, it relates to a method in which a portion of the aromatic compound is incompletely side chain chlorinated, the unreacted aromatic compound is separated from the incompletely side chain chlorinated aromatic compound, and the incompletely side chain chlorinated aromatic compound is further side chain chlorinated.
&agr;,&agr;,&agr;,&agr;′,&agr;′,&agr;′-hexachloro-m-xylene (HCMX) is used to make fluorinated solvents and other chemicals. It is made by chlorinating m-xylene. (See, for example, U.S. Pat. No. 4,029,560.) While chlorinating m-xylene is effective in making HCMX, it can result in 40 to 50% of the product being ring chlorinated when run as a continuous process; the ring chlorinated material is disposed of as waste.
SUMMARY OF THE INVENTION
We have discovered that ring chlorination of toluene, xylenes, and mesitylenes is greatly reduced if unreacted aromatic compound is removed after some of it has been chlorinated. In our invention, we partially chlorinate only a portion of the aromatic compound, then separate and recycle the unreacted aromatic compound. The partially chlorinated aromatic compound is then further chlorinated. This procedure chlorinates the side chains of aromatic compounds with the production of less than 12% ring chlorinated compounds when run as a continuous process.
We have found that it is primarily the unreacted aromatic compound that is ring chlorinated and that once aromatic compound is at least partially side chain chlorinated, it is protected from ring chlorination. While we do not understand the mechanism and do not wish to be bound by any theories, we believe that the side chain chlorinated aromatic compound may help catalyze the ring chlorination of unreacted aromatic compound.
Ring chlorination occurs to a greater extent in metal reactors than in glass reactors. Typically, there is about 15 to about 25% ring chlorination in a 1 L metal-lined reactor, but only about 5 to about 10% ring chlorination under the same conditions in a 1 L glass reactor. Nickel and other metals are known to catalyze ring chlorination. In the prior art process, sequesterants are added to reduce the catalytic effect of metals on ring chlorination. Yet, in the process of our invention, little or no additional ring chlorination occurs in the presence of nickel, even when a sequesterant is not present.
More ring chlorination also occurs if the process is performed continuously, rather than semi-batch (i.e., the aromatic compound is batch, the chlorine is continuous). Typically, there is about 40% ring chlorination in a continuous process, but only about 12% ring chorination under the same conditions in a batch process. That is unfortunate because greater throughput can be achieved using a continuous process. Nevertheless, in the process of this invention the amount of ring chlorination in a continuous process is comparable to the amount of ring chlorination in a prior art batch process.
Finally, the chlorination of aromatic compounds results in the formation of dimers and trimers, which have no value and must be disposed of. We have found that vacuum distilling the product greatly reduces the formation of dimers and trimers.
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Bushey George J.
Czupski Leonard M.
Lindrose Mark E.
Rhodes C. Duncan
Brookes Anne E.
Fuerle Richard D.
Gorgos Kathryn
Occidental Chemical Corporation
Tran Thao
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