Organic compounds -- part of the class 532-570 series – Organic compounds – Nitriles
Patent
1996-04-18
1998-03-31
Richter, Johann
Organic compounds -- part of the class 532-570 series
Organic compounds
Nitriles
570170, 570174, 570206, 570207, C07C25510, C07C 17156, C07C 2513
Patent
active
057340730
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB95/01738 filed Jul. 24, 1995.
FIELD OF THE INVENTION
The present invention relates to halogenation reactions, in particular to methods for the iodination or bromination or chlorination of aromatic compounds.
BACKGROUND AND SUMMARY OF THE INVENTION
Known procedures for the direct iodination of benzenoid compounds are limited. Some of the most effective known procedures involve the use of iodine in nitric acid, N-iodosuccinimide in triflic acid, decomposition of organomercurytrifluoroacetates in iodine-potassium iodide-dimethylformamide mixtures and iodine chloride. However, these procedures have a variety of limitations including inconvenience, limited reactivity and environmental unacceptability. Iodine fluoride has been made from iodine and fluorine and this provides a very effective iodinating agent. However, low temperatures have been required to produce the iodine fluoride.
According to the present invention there is provided a method of iodinating and/or brominating and/or chlorinating an aromatic compound which comprises the steps of reacting an iodinating agent and/or a brominating agent and/or chlorinating agent with the aromatic compound in the presence of elemental fluorine.
The iodinating agent may comprise elemental iodine or any one or more interhalogen compounds (such as ICl or IBr) and the brominating agent may comprise elemental bromine or one or more interhalogen compounds (such as BrF or BrF.sub.3) and the chlorinating agent may comprise elemental chlorine or interhalogen compounds (such as ClF or ClF.sub.3).
Surprisingly, we have now found that we can promote controlled iodination and/or bromination and/or chlorination of aromatic compounds by a method which can be simpler than, and does not possess the disadvantages of the prior art methods. The reaction may be carried out at ambient temperature, e.g. 20.degree. C., and therefore no special heating or cooling steps are required. Furthermore, the yields obtained by the method according to the present invention may be greater than those obtained for prior art methods as illustrated hereinafter. Polyiodination and polybromination and polychlorination are easily achieved by simple adjustment of the stoichiometry of the reaction employed in the method.
The method according to the present invention may be carried out by passing fluorine gas into a liquid which contains the aromatic compound and the iodinating and/or brominating agent and/or chlorinating agent. The reaction may be carried out in a vessel in which the liquid is present or alternatively a flowing stream of the liquid may be contacted with a gaseous flow of fluorine in countercurrent fashion.
The said liquid may comprise a solvent for the aromatic compound and/or a solvent for the fluorine. If two or more solvents are employed these may or may not be miscible with one another.
The solvent for the aromatic compound may comprise an acid which may for example comprise an organic acid which may be a carboxylic acid such as formic acid, acetic acid or trifluoracetic acid or alternatively an inorganic acid such as sulphuric acid or trifluoromethanesulphonic acid or fluorosulphuric acid or hydrogen fluoride or antimony pentafluoride/hydrogen fluoride.
The solvent for the fluorine may comprise a fluorinated organic liquid such as a fluorinated alkane, e.g. CF.sub.2 ClCFCl.sub.2 or a perfluorocarbon, e.g. a perfluoroalkane, or perfluorodecalin, or a fluorinated ether, or a perfluorinated ether or partly fluorinated systems such as a polyfluoroalcohol.
The present invention is suitable for the iodination or bromination or chlorination of a range of aromatic compounds. Thus, the aromatic compound which by the method of the present invention is iodinated or brominated or chlorinated is preferably benzene or naphthalene which may be substituted by from one to five substituents. Suitable substituents which may themselves be optionally substituted may be independently selected from: alkyl, alkoxy, halogen, --CN, --OH, --NO.sub.2, --NH.sub.2, --NHalkyl, -
REFERENCES:
patent: 2716140 (1955-08-01), McBee et al.
patent: 4621160 (1986-11-01), Desbois et al.
Rozen et al J. of. Org. Chem. vol. 55, 1990 pp. 3552-3555.
Atherton Malcolm John
Chambers Richard Dickinson
Moilliet John Stewart
Skinner Christopher John
BNFL Fluorochemicals Ltd
Richter Johann
Sackey Ebenezer
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