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AssigneeHoechst Aktiengesellschaft
InventorsRudolf Lademann, Helmut Lindner, Thomas Martini, Peter Paul Rammelt
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Preparation of derivatives of benzene containing CF.sub.3 groups from the corresponding compounds containing CCl.sub.3 groups (e.g. trichloromethyl benzene) is carried out continuously with excellent yield rates by reaction with liquid hydrogen fluoride in an autoclave above 80.degree.C, (which latter exceeds the stoichiometric proportion by at least 25 mole %). The reactants are fed continuously into the autoclave. The reaction mixture preferably becomes pressurized to at least 20 atmospheres and homogeneous after having reached a certain filling level. The reaction mixture is thereafter withdrawn proportionally to its feeding-in rate. The mixture may be conveyed through one or several additional autoclaves with the final withdrawal of the reaction mixture being out from the terminal autoclave of this cascade. The fluorination products are well known starting and inermediate products for the preparation of dyestuffs and pesticidal compositions.
In a process for the preparation of the derivative of benzene containing at least one trifluoromethyl group by reaction of the corresponding trichloromethyl compound with liquid hydrogen fluoride, by subsequently distilling the reaction products under pressure thus eliminating the newly formed hydrogen chloride, and by subsequently isolating the remaining reaction products, the improvement for continuous processing which comprises continuously feeding the reactants into a reaction zone under an effective pressure in excess of 20 absolute atmospheres to maintain a sufficiently homogeneous reaction mixture to solubilize the reactants, with the hydrogen fluoride reactant being in at least a 25 mol % excess as compared to the stoichiometric proportion, blending said mixture in said zone by means limited to the agitation caused by the pressurized feeding of the reactants into said zone, withdrawing the reaction products from said zone proportionately to the feeding-in rate of the reactants, said reaction zone being maintained in a reaction temperature range of above 80.degree. to about 150.degree.C, said reaction having been initiated by precharging said zone with liquid hydrogen fluoride alone or in homogeneous mixture with said trichloromethyl compounds and hydrogen chloride to a pressure of at least 20 atmospheres.
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