Hoechst Aktiengesellschaft

Rudolf Rossmeissl

Steffen Dapperheld

Detlef Kampmann

Frank Ebmeyer

Gerhard Ullmann

Werner Lindner

Hans Milluwe

Ulf Otto Paulus-Von Russdorf

Klaus Kretschmann

Hans-Karl W Vom Baur, Deceased

The present invention relates to a process for the preparation of a particularly pure monochloroacetic acid, in which, in a first step, a hydrogenation of a mixture of mono- and dichloroacetic acid is carried out to a residual content of dichloroacetic acid of 400 to 600 ppm and, in a second step, this mixture is subjected to melt crystallization. The hydrogenation is carried out with a heterogeneous catalyst which comprises 0.1-5.0% by weight of palladium and in which active charcoal or silicon dioxide is used as the support.

Process for the preparation of a particularly pure monochloroacetic

Trichloroacetic and dichloroacetic acid are dehalogenated to give monochloroacetic acid by electrolyzing aqueous solutions of these acids in divided electrolysis cells using carbon cathodes; the aqueous electrolytic solutions also contain one or more metal salts having a hydrogen overvoltage of at least 0.4 volt (at a current density of at least 4000 A/m.sup.2) and specific ammonium and/or phosphonium salts. In this process, there is an extremely small evolution of hydrogen at the cathode, even at a very low concentration of the polychlorinated acetic acid, without the high selectivity of conversion of the electrolysis being impaired in continuous operation.

Partial electrolytic dehalogenation of dichloroacetic and

In the electrode in the form of a rectangular parallelepiped composed of impregnated graphite material for electrochemical reactors, the electrode (4,5) is provided with openings (8,9,10,11) extending perpendicular to its active electrode surfaces (6,7) at its corners. Canals (12,13) which extend parallel to the active electrode surfaces (6,7) in the direction of an adjacent opening (9,10) originates in each case from two openings (8,10) situated diagonally opposite each other. The canals (12,13) have communicating channels (14,15) to the active electrode surfaces (6,7).

Electrode for electrochemical reactors

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Mertingen, Germany

Rudolf Rossmeissl