These reactions lead to the formation of fluorobenzene derivatives FC 6 H 4 R isomer mixture together with isomeric difluorobenzenes and fluorinated and non-fluorinated biphenyls. The results have been compared with previously reported data obtained in other solvents using other catalysts.
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Filler, R. CrossRef Google Scholar. Tius, M. Bardin, V. Google Scholar. Yagupolskii, Y. Zajc, B. Frohn, H. Brel, V. Tyrra, W. Inorganic Chemistry Highlights , Meyer, G. Yang, N. Hyman, H. MacKenzie, D. Shaw, M. Anand, S. Rabinovitz, M.
Fluorine Chem. Fedorov, A. Maletina, I. R 3 represents optionally substituted radicals from the series comprising alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl and aralkyl,. It is decidedly surprising that the process according to the invention can be carried out so simply and easily.
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It especially represents a general access to compounds of the formula I which were hitherto unavailable in industrial quantities. In particular, it is surprising that compounds of the formula IV can be obtained in such a good yield and purity even when R 2 represents halogen. It was to be expected then that the halogen atom R 2 would additionally also be substituted by OR 3 and one or two allylic fluorine atoms would optionally be substituted J.
Park et al. It is furthermore surprising that the allylic fluorine atoms are not removed hydrogenolytically in the hydrogenations, as would have been expected, for example, according to the literature compare M. Hudlicky, J. Fluorine Chem. It was furthermore not to be expected that the ether cleavage would lead so selectively to the partially fluorinated alcohols of the formula I and no competing elimination would take place. In the formulae I to V , R and R 1 independently of one another preferably represent alkyl having 1 to 10, preferably 1 to 8, in particular 1 to 4 carbon atoms, which is monosubstituted or polysubstituted by fluorine, cycloalkyl having 3 to 10, preferably 3 to 6, in particular 3 to 5 carbon atoms, which is monosubstituted or polysubstituted by fluorine, or R and R 1 together represent the group -- CF 2 -- n , where n represents 2, 3 or 4, n preferably represents 2 or 3 and n in particular represents 2.
For alkyl in R and R 1 , methyl, ethyl, n- or isopropyl, n-, iso-, sec. Alkyl is preferably monosubstituted to nonasubstituted by fluorine, in particular monosubstituted to pentasubstituted. Trifluoromethyl may be mentioned in particular. For cycloalkyl in R and R 1 , cyclopropyl, cyclopentyl or cyclohexyl may be mentioned as examples. The cycloalkyl radical in R and R 1 , if it is substituted, is preferably monosubstituted to dodecasubstituted, in particular monosubstituted to hexasubstituted, very particularly monosubstituted to tetrasubstituted, by fluorine.
The Hal radical in the formula II preferably represents fluorine, chlorine or bromine, in particular fluorine or chlorine. The R 2 radical in the formulae II and IV represents hydrogen, fluorine, chlorine or bromine, in particular hydrogen, fluorine or chlorine.
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The R 3 radical in the formulae III and V preferably represents in each case optionally substituted alkyl having 1 to 8, in particular 1 to 5 carbon atoms, alkenyl having 3 to 10, in particular 3 to 7 carbon atoms, cycloalkyl having 3 to 6 carbon atoms such as cyclopropyl, cyclopentyl or cyclohexyl, cycloalkenyl having 4 to 10, in particular 4 to 7 carbon atoms, phenyl, naphthyl, pyridyl, pyrimidyl or phenylalkyl having 1 to 4, in particular 1 or 2 carbon atoms, in the alkyl moiety.
Substituents selected are halogen, in particular fluorine and chlorine, alkoxy having 1 to 10, preferably 1 to 6, in particular 1 to 4 carbon atoms, for example methoxy, ethoxy, n- or i-propoxy, and 1 or 2 oxo groups. In particular, R 3 in the formulae III and V represents primary, secondary or tertiary, preferably secondary or tertiary, alkyl having 3 to 6 carbon atoms, cyclohexyl, benzyl or phenyl.
For alkyl in R 3 , methyl, ethyl, n-propyl, i-propyl, n-butyl, s-butyl and t-butyl may be mentioned as examples. Particularly preferred R 3 represents i-propyl, phenyl, benzyl or cyclohexyl. Partially fluorinated alkyls of the formula I in which R and R 1 together represent the group -- CF 2 n --, where n represents 2, 3 or 4, n preferably represents 2 or 3 and n in particular represents 2, can be prepared particularly advantageously by the process according to the invention.
The course of the process according to the invention can be illustrated by the following equation: STR5. The compounds of the formulae II and III required for carrying out the process according to the invention are known synthesis chemicals or can be prepared by known methods. The reaction of the alkene of the formula II with an alcohol of the formula III step a is carried out in the presence of a base and, if appropriate, in the presence of a diluent.
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Suitable bases for this purposes are alkali metal and alkaline earth metal hydroxides, tertiary amines or alkoxides. Alkali metal and alkaline earth metal hydroxides and tert. NaOH and triethylamine are particularly preferred. Possible diluents for step a are all inert organic solvents. Examples of these are alkyl ethers, hydrocarbons, partially or perhalogenated hydrocarbons and also optionally substituted aromatic hydrocarbons.
The alcohol of the formula III employed may also be used itself as a solvent. If desired, diluents can be completely dispensed with. The reaction temperatures can be varied within a relatively wide range when carrying out the process according to the invention step a. The process according to the invention is in general carried out at normal pressure, but it can also be carried out at elevated or reduced pressure. The ratio of the materials of the formulae II and III used when carrying out the process according to the invention step a is not critical and may be Ratios of The metals ruthenium, rhodium, palladium, platinum, cobalt and nickel and their compounds are preferred here.
The hydrogenation catalysts may consist exclusively or predominantly of hydrogen-transferring substances, but the latter may also be applied to support materials. Examples of suitable support materials for the hydrogen-transferring substances are: inorganic materials such as kieselguhr, silica, aluminas, alkali metal and alkaline earth metal silicates, aluminium silicates, montmorillonite zeolites, spinels, dolomite, kaolin, magnesium silicates, zirconium oxide, zinc oxide, calcium carbonate, silicon carbide, aluminium phosphate, boron phosphate, asbestos, active carbon or barium sulphate, but also organic materials, for example naturally occurring or synthetic compounds having high molecular weights such as silk, polyamides, polystyrenes, cellulose or polyurethanes.
Inorganic support materials are preferred. The support material may be present, for example, in the form of beads, extrudates, filaments, cylinders, polygons or in powder form. Support catalysts of this type can in general contain 0.
Houben-Weyl Methods of Organic Chemistry Vol. E 10a, 4th Edition Supplement - Google книги
The hydrogen-transferring substance can in this case be homogeneously distributed in the support material, but catalysts are preferred in which the hydrogen-transferring substance is deposited in the outer layer or on the surface. The preparation and the shaping of catalysts which can be used in the process according to the invention can be carried out in a known manner see, for example, Houben-Weyl, Methoden der organischen Chemie Methods of Organic Chemistry , volume IV, 1c, part I, pp. Preferred support catalysts are ruthenium on carbon, ruthenium on alumina, rhodium on carbon, rhodium on alumina, palladium on carbon, palladium on alumina, palladium on calcium carbonate, palladium on barium sulphate, palladium on silica, platinum on carbon and platinum on alumina.
Particularly preferred catalysts for the process according to the invention step b are palladium on carbon, palladium on alumina, palladium on silica and palladium on calcium carbonate. The hydrogenation catalyst can be employed in the process according to the invention, for example, in amounts of 0. This amount is preferably 0. Mixtures of two or more of the hydrogenation catalysts mentioned can also be used to carry out the process according to the invention and, if appropriate, catalyst is added during the reaction. The process according to the invention step b can be carried out in the liquid phase in the absence of a diluent.
Preferably, however, the reaction is carried out using a diluent. Suitable diluents are all organic solvents which are inert under the reaction conditions, for example aliphatic and cycloaliphatic hydrocarbons, such as hexane, heptane, octane, cyclohexane, methylcyclohexane and decalin; aliphatic or alicyclic ethers, such as diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, methyl butyl ether, ethyl butyl ether, ethylene glycol dimethyl ether, 1,3-dioxolane, 1,4-dioxane and tetrahydrofuran; lower aliphatic alcohols, such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, tert.
Water can also be employed. Alkanecarboxylic acids, such as acetic acid, propionic acid, hexanoic acid etc. Preferred solvents are cycloaliphatic hydrocarbons or aliphatic ethers, in particular cyclohexane, methyl-cyclohexane, tetrahydrofuran, 1,4-dioxane, water and acetic acid. If a base is used in step b, those which are suitable are, for example, alkali metal and alkaline earth metal hydroxides and carbonates, tertiary organic amines or alkoxides.
Alkali metal and alkaline earth metal hydroxides and carbonates and also tertiary amines are preferred. Sodium hydroxide and potassium hydroxide, sodium carbonate and potassium carbonate, triethylamine and pyridine are particularly preferred. The process according to the invention step b can be carried out in a wide temperature range. The hydrogen pressure during the hydrogenation is not critical and may extend, for example, from 1 to bar.
It may be advantageous to compensate for hydrogen consumed by means of a further addition. Preferred hydrogen pressures are from 5 to bar, in particular from 20 to bar. These are converted, if desired after their isolation, into compounds of the formula I using ether-cleaving agents. In the hydrogenation, in the case of aromatic R 3 radicals, the aromatic radical can additionally hydrogenated. In this way, the meaning of R 3 can be changed from, for example, phenyl to cyclohexyl compare Preparation Example 9.
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So-called "soft" nucleophiles, such as, for example, iodide for example as the lithium or potassium salt or alkyl sulphides can also be used as ether-cleaving agents. Strong Bronsted acids and Lewis acids are preferred. If appropriate, the ether cleavage may be carried out in the presence of a diluent.
Related Houben-Weyl Methods in Organic Chemistry: B. Synthesis of Fluorinated Compounds
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