Hoechst Aktiengesellschaft

Hartmut Behringer

Heinrich Rehberg

Kurt Karrenbauer

Azo pigments are made by subjecting a diazo component to an azo coupling reaction with the equivalent quantity of a coupling component difficultly soluble at less than 65.degree. C. in the aqueous/acid and aqueous/netural pH-ranges. More specifically, an aqueous/alkaline solution of the coupling component is continuously mixed in a first reaction step with an aqueous solution of acetic acid, boric acid, phosphoric acid, hydrochloric acid or sulfuric acid at a temperature lower than 65.degree. C. within a period of less than 1 minute, during which the coupling component commenences precipitating at least partially as reactive matter; next, the suspension obtained is continuously mixed, in a second reaction step immediately following the first reaction step, with an aqueous/acid solution of the diazo component at a temperature of less than 65.degree. C. within a period of less than 1 minute, and a predetermined pH between 2 and 9 is established by controlling the flow of the mass streams of diazo component and coupling component whereby a portion of the coupling component is caused to undergo immediate reaction to the azo pigment to be made; the balance portion of the coupling component is ultimately reacted in a postreaction phase with unreacted diazo component to the azo pigment to be made.

Process for making azo pigments

Azo Pigments are made by subjecting a diazo component to an azo coupling reaction with the equivalent quantity of a coupling component difficultly soluble at less than 65.degree. C. in the aqueous/acid and aqueous/neutral pH-ranges. More specifically, an aqueous/acid-solution of the diazo component is continuously mixed at a temperature of less than 65.degree. C. within a period of less than 1 minute with the aqueous/alkaline solution of the coupling component and a predetermined pH between 2 and 9 is established by controlling the flow of the mass streams of diazo component and coupling component; in this way a portion of the coupling component is caused to undergo immediate reaction to the azo pigment to be made whereas the balance portion of the coupling component simultaneously commences precipitating as finely crystalline reactive matter, which is reacted in a post-reaction phase with unreacted diazo component to give the azo pigment to be made.

The invention relates to a process for the continuous manufacture of azo pigments, wherein a coupling component is reacted, inside a reaction zone filled with a previously produced suspension of the azo pigment to be made, with an aqueous solution of a diazo component at 10.degree. to 60.degree. C. and over periods of 0.2 to 4 hours. To this end, an aqueous suspension or solution of the coupling component is passed in substantially laminar flow upwardly through a cylindrical reaction zone arranged in upright position; the aqueous solution of the diazo component is introduced through 2 to 50 serially arranged inlets opening laterally into the reaction zone, the diazo component being admitted in quantities decreasing from below to above and the stoichiometric end point of the coupling reaction being established at the upper most inlet opening into the reaction zone; the pH-value typical of each reaction is established by introducing dilute alkali liquor through 2 to 50 serially arranged inlets opening laterally into the reaction zone, the respective diazo component and alkali liquor inlets being arranged at different levels with respect to each other.

Continuous production of azo pigments

The disclosure relates to a process for controlling diazotization reactions. To this end, a reaction batch containing an aromatic amine and nitrous acid is vigorously agitated so as to continuously renew the surface area of the batch. The air above said surface area is exhausted at a constant rate and tested for its content of nitrous gases originating from partially decomposed nitrous acid. Nitrous acid or dissolved matter forming it under the reaction conditions is supplied to the feed amine in the proportions necessary to provide for a content between 5 and 300 ppm nitrous gases in the exhausted air.

Process for controlling diazotization reactions involving nitrous

The invention provides a process for the continuous diazotization of primary aromatic amines by reacting an aqueous solution or suspension of the amine in a mineral acid with an aqueous sodium nitrite solution. To this end, the lower portion of a cylindrical diazotization vessel placed in upright position is fed continuously with an aqueous mineral acid solution or suspension of a diazotizable primary aromatic amine. At the same time, the vessel is fed, via one or more inlets arranged one above the other so as to open laterally thereinto, with an aqueous sodium nitrite solution, the amine and nitrite being used in stoichiometric proportions, or the nitrite being used in a stoichiometric deficiency and the acid being used in an excess of about 1 to 3 equivalents per amine equivalent in the mineral acid solution. The resulting mixture is reacted while producing a laminar flow of liquid matter at temperatures of about 5.degree. to 30.degree. C. Next, reaction mixture is removed, in accordance with the diazotization velocity of the particular amine used, from the upper portion of the diazotization vessel at a place where the reaction mixture is substantially free from nitrous acid, said place being situated in the vessel at a level which is the higher the lower the diazotization velocity of the amine used. The reaction mixture removed is finally filtered and diazonium salt-containing solution is delivered to a sojourn zone.

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Erftstadt, Germany

Hartmut Behringer