Hoechst Aktiengesellschaft

Thomas Vollheim

Hans Schafer

Eberhard Ritter

Martin Schottler

Process for the preparation of 2,5-di(phenylamino)terephthalic acid and dialkyl esters thereof in high purity. The invention relates to a process for the preparation of dialkyl 2,5-di(phenylamino)terephthalates of the formula (I) ##STR1## in which R is a hydrogen atom or a methyl group and R' is a methyl group or ethyl group, by dehydrogenation (oxidation) of the corresponding dialkyl 2,5-di(phenylamino)-3,6-dihydroterephthalate with oxygen, which comprises blanketing with oxygen a solution or suspension of the dialkyl 2,5-di(phenylamino)-3,6-dihydroterephthalate in aromatic hydrocarbons in a stirred vessel, circulating this reaction mixture via a spraying device, so that the sprayed reaction mixture is distributed over the reaction mixture present in the stirred vessel, the sprayed reaction mixture being mixed with the circulating gas. The process has the advantage of a short reaction time, combined with favorable space-time yields and simplicity in terms of apparatus.

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Hanau, Germany

Thomas Vollheim