Abstract: In the preparation of substituted 4,4'-diaminostilbene-2,2'-disulfonic acid salts a clear increase in the reaction rate may be achieved by carrying out the reaction of the tetrachlorine derivative (III) with the aniline (IV) in the presence of the amine (VI) as acid-absorber.

Abstract: This invention relates to a continuous process for the preparation of quinacridone pigments by(a) preparing a reaction mixture by mixing(i) a 2,5-dianilinoterephthalic acid or ester thereof, and(ii) at least about 0.5 parts by weight, per part of component (a)(i), of a dehydrating agent;(b) passing the reaction mixture through a continuous reactor having one or more heated zones at a temperature of about 80.degree. C. to about 300.degree. C. to form a crude quinacridone composition; and(c) mixing a continuous stream of the crude quinacridone composition with a liquid in which the quinacridone pigment is substantially insoluble at a ratio of about 0.5 to about 15 parts by weight of the liquid per part by weight of the crude quinacridone composition.

Abstract: A process for the preparation of compounds of the formula (I) ##STR1## wherein n represents 0-2;M represents H, alkali metal ion or optionally substituted ammonium ion; andX represents anilino, N- or N,N-alkylamino;by reaction of a compound of the formula (IV) ##STR2## with 2 molar equivalents of an amnine of the formula X--H, at a pH of 5-10, optionally in the presence of an acid-trapping agent which differs from X--H, wherein the compound of the formula (IV) is added to an aqueous reaction medium with a temperature of at least 40.degree. C. and the amine of the formula X--H and, optionally, the acid-trapping agent are added to the aqueous reaction medium independently of one another and/or during and/or after the addition of IV. The compounds of the formula I which are outstandingly suitable as optical brighteners.