Process for the preparation of benzophenthiones and benzophenone

Details Process for the preparation of benzophenthiones and benzophenone Process for the preparation of benzophenthiones and benzophenone

1996-11-18

1998-07-07

Ivy, C. Warren

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568 20, C07C 4542, C07C32502

Patent

active

057771723

DESCRIPTION:

BRIEF SUMMARY
This application is the national phase of international application PCT/GB95/01101, filed May 16, 1995 which designated the U.S.
This invention relates to a process for the preparation of optionally substituted benzophenthiones, and especially 4,4'-difluorobenzophenthione and processes for their conversion to the corresponding benzophenones and to certain benzophenthiones.
4,4'-Difluorobenzophenone (4,4'-DFBP) is an important intermediate in the preparation of high performance polymers, such as PEEK and PES, but to make polymers with high performance properties it is essential to start with relatively pure 4,4'-DFBP, which is substantially free from the other positional isomers. Furthermore the 4,4'-DFBP, to be suitable for use in high performance polymers, must be substantially free from coloured impurities and polymeric by-products.
It is known to make di-substituted benzophenones by reaction of a mono-substituted benzene with phosgene in the presence of a Friedel-Craft's catalyst ("F-C Cat"), especially a Lewis acid, such as FeCl.sub.3 or AlCl.sub.3. While this reaction has a high overall yield, it leads to the production of a mixture of isomers in which the 4,4'-isomer, though predominant, represents only around 75% of the total mixture, the remainder being mainly 3,4'- and 2,4'-isomers.
It has now been surprisingly discovered that the use of thiophosgene (CSCL1.sub.2) in place of phosgene, in the acylation of fluorobenzene gives a mixture of isomeric difluoro-benzophenthiones, containing a significantly higher proportion (>90%) of the 4,4'-isomer. This process is also applicable to other substituted, especially mono-substituted, benzenes. The thione(s) can be converted into the equivalent ketone(s) by hydrolysis or oxidation and the present invention also provides novel processes for effecting these conversions.
According to the present invention there is provided a process comprising the reaction of an optionally substituted benzene with thiophosgene in the presence of a Friedel-Craft's catalyst for the preparation of the equivalent optionally substituted benzophenthione.
In one aspect of the present invention, in which the benzene is mono-substituted, the process to form an optionally substituted benzophenthione may be represented by the following reaction scheme: ##STR1## in which X is H, halogen, alkyl, alkoxy, CN and dialkylamino.
Where X is halogen it is preferably chlorine, fluorine or bromine and more preferably fluorine.
Where X is alkyl it is preferably C.sub.1-6 -alkyl, more preferably C.sub.1-4 -alkyl.
Where X is alkoxy it is preferably C.sub.1-6 -alkoxy, more preferably C.sub.1-4 -alkoxy.
Where X is dialkylamino it is preferably di(C.sub.1-6 -alkyl)amino. X is preferably halogen, alkyl or alkoxy, more preferably --F, --Cl, C.sub.1-4 -alkyl or C.sub.1-4 -alkoxy.
It is further preferred that the benzene contains only one substituent (represented in the reaction scheme above by X) and that this is halogen, and more especially fluorine. The benzene may contain other substituents, provided they do not interfere with the reaction to produce the desired 4,4'-isomer. Examples of optionally substituted benzenes are benzene itself, fluorobenzene, chlorobenzene, brombenzene, toluene, anisole,,cyanobenzene and diethylaminobenzene.
The Friedel-Craft's catalyst is preferably a Lewis acid, more preferably FeCl.sub.3 or AlCl.sub.3 and especially AlCl.sub.3.
The reaction is preferably carried out at a temperature from 0.degree. C. to 100.degree. C., more preferably at from 0.degree. C. to 80.degree. C. and especially at from 0.degree. C. to 40.degree. C. Lower temperatures generally lower the reaction rate to below reasonable levels and higher temperatures tend to reduce the selectivity, reducing the proportion of 4,4'-isomer in the mixture. In the preferred temperature range the process typically takes approximately four hours to complete.
The reaction may be carried out in a medium which is liquid over the preferred temperature range, but it is preferred to use the optionally substituted benzene itse

REFERENCES:
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Bergreen: "Untersuchungen uber das Thiophosgen", Berichte der Deutschen Chemischen Gesellschaft, vol. 21, 1888, pp. 337-352, see p. 341.
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