Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Patent
1996-10-25
1999-05-04
Rotman, Alan L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
560 8, 562125, 562840, 568812, 568936, 570143, 570147, C07C25550, C07C 6976
Patent
active
059005025
DESCRIPTION:
BRIEF SUMMARY
This application is 371 of PCT/GB94/02732, filed Dec. 12, 1994, which is now published as WO95/16649 on Jun. 22, 1995.
This invention relates to a process for the fluorination of aromatic compounds.
Processes for the fluorination of aromatic compounds are known where fluorine gas is used as a fluorinating agent but the strong oxidising properties of fluorine cause the aromatic compound to decompose and poor yields of the required products are obtained. The dilution of the fluorine gas with an inert gas, such as nitrogen, is described in EP-A2-0512715 and this moderates the oxidising effect of the fluorine allowing the introduction of one fluorine atom into the aromatic compound in good yield. Known processes for the preparation of polyfluoroaromatic compounds involves using more severe fluorinating conditions with a consequent increase in the formation of decomposition products or involves halogen exchange or reaction of an aromatic compound with a fluorinating agent such as cobalt trifluoride.
The direct fluorination of certain aromatic compounds in acetonitrile is known but is generally inconvenient because low reaction temperatures are required. Further problems occur where fluorination is carried out in solvents such as acetonitrile since reaction with the solvent leading to tar formation can occur.
The object of the present invention is to provide a fluorination process for making specific fluorinated compounds by the selective introduction of one or more fluorine atoms into an aromatic compound in good overall yield which may be operated at easily obtainable temperatures and which minimises reaction between fluorine and the solvent.
According to the present invention there is provided a process for the selective introduction of one or more fluorine atoms into a disubstituted aromatic compound by reaction of the aromatic compound in an acid medium with fluorine gas characterised in that the acid medium has a dielectric constant of at least 20 and a pH of less than 3.
The present process provides a cost effective means of selectively introducing one or more fluorine atoms into an aromatic compound in good overall yield.
The aromatic compound is preferably benzene which may be substituted by from one to five substituents. Suitable substituents may be independently selected from alkyl, alkoxy, halogen, --CN, --OH, --NO.sub.2, --N(alkyl).sub.2, --NHCOalkyl, --COOalkyl, --COOH, --COalkyl, --CON(alkyl).sub.2, --COY, --CY.sup.1.sub.3 and --SO.sub.2 Y.sup.2 in which Y is --H, --F, --Cl, --Br, Y.sup.1 is --F or --Cl, and Y.sup.2 is --F, --Cl, --Br, --N(alkyl).sub.2. In each of these substituents alkyl is preferably C.sub.1-4 -alkyl, alkoxy is preferably C.sub.1-4 -alkoxy and halogen is preferably --F, --Cl or Br.
Preferred substituents for the aromatic compound are selected from --CN, --OH, --NO.sub.2, --NHCOCH.sub.3, --OCH.sub.3, --COOCH.sub.3, --COOH, --COCH.sub.3, --CH.sub.3, --Cl, --Br and --F and combinations thereof. The aromatic compound is preferably disubstituted in the 1- and 4-positions or in the 1- and 2-positions and more preferably disubstituted in the 1- and 4-positions.
Where the aromatic compound is disubstituted the 1-position is preferably occupied by a meta-directing group and the 2- or 4-position is preferably occupied by an ortho/para-directing group.
In a preferred embodiment of the present invention the aromatic compound is of Formula (1): ##STR1## wherein:
R.sup.1 is a meta-directing group; ortho/para-directing group; is --H.
The meta-directing group represented by R.sup.1 is preferably selected from --Br, --Cl, --F, --NO.sub.2, --CN, --COY, --CY.sup.1.sub.3 and --SO.sub.2 Y.sup.2 in which Y is --H, --F, --Cl, --Br, --C.sub.1-4 -alkyl, --OH or --OC.sub.1-4 -alkyl;
Y.sup.2 is --F, --Cl, --Br, --NH.sub.2, --NH(C.sub.1-4 -alkyl) and --NH(C.sub.1-4 -alkyl).sub.2.
The ortho/para-directing groups represented by X.sup.1, X.sup.3 and X.sup.5 are preferably selected from --OH, --OC.sub.1-6 -alkyl, C.sub.1-6 -alkyl and --NHCOC.sub.1-6 -alkyl.
Where one of the groups represented by X.sup.2 and X.
REFERENCES:
patent: 5212301 (1993-05-01), Moilliet et al.
Chambers Richard Dickinson
Hutchinson John
Skinner Christopher John
Thomson Julie
Aulakh Charanjit S.
BNFL Fluorochemicals Limited
Rotman Alan L.
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