Abstract: Isoindolenines of the general formula (I) ##STR1## where R.sup.1 is hydrogen, unsubstituted or chlorine-, hydroxylphenyl- or cyano-substituted C.sub.1 -C.sub.12 -alkyl or C.sub.5 -C.sub.8 -cycloalkyl or unsubstituted or chlorine- or methyl-substituted phenyl,R.sup.2 is hydrogen or unsubstituted or chlorine-, hydroxyl-, phenyl- or cyano-substituted C.sub.1 -C.sub.6 -alkyl, or is morpholino, pyrrolidino or piperidino, andR.sup.3 is hydrogen or methyl and the benzene ring A may be substituted by from 1 to 4 chlorines, 1 or 2 C.sub.1 -C.sub.4 -alkyls or 1 nitro,are obtained by condensing 3-aminophenols of the formula (II) ##STR2## with 3-amino-1-oxoisoindolenines of the general formula (III) ##STR3## in the presence of acids, and are hydrolyzible in very good yields into benzoylbenzoic acids (IV) ##STR4## which are very difficult, if not impossible, to prepare by prior art methods.

Abstract: A process for the preparation of a water soluble food-grade diaminotriphenylmethane colorant containing from 2 to 4 sulfo groups, comprising anodically oxidizing the corresponding leuco compound in an electrolysis cell divided into an anode space and a cathode space in the presence of from 0.01 to 2% by weight, based on the solution being oxidized, of a C.sub.2 -C.sub.4 -alkanol, urea, a urea derivative or a mixture thereof, at a potential .epsilon..sub.h .ltoreq.1250 mV and at a temperature .ltoreq.+40.degree. C. The colorants obtained are produced in high yield and are of food quality.