Abstract: Very pure riboflavin (I) is obtained by a process in which the riboflavin is dissolved in dilute aqueous alkali metal hydroxide solution, if necessary the alkaline solution is purified by treatment with active carbon or with a solvent which is insoluble or only slightly soluble in water, the resulting alkaline solution of I is introduced into water which is at 90.degree.-100.degree. C. and to which an acid has been added in an amount such that the reaction mixture is brought to a pH of from 6.5 to 0.8, the temperature being maintained at from 40.degree. to 100.degree. C., the reaction mixture is kept at from 90.degree. to 100.degree. C. for from 10 to 80 minutes and cooled, and I is then isolated.

Abstract: Riboflavin of the formula I ##STR1## is prepared by condensation of a 4,5-dimethyl-N-(D)-ribityl-2-phenylazoaniline of the formula II ##STR2## where X is H, --Cl, --NO.sub.2 or --CH.sub.3 in the o- or p-position, with barbituric acid of the formula III ##STR3## in the presence of an acidic condensing agent in an inert organic solvent by an improved process in which the reaction is carried out in an aliphatic diol or triol derivative of the general formula IV ##STR4## where R.sup.1 is H or CH.sub.3, R.sup.2 is H or CH.sub.3 -- or, when n is 0, is CH.sub.3 --CO--O--CH.sub.2 --, R.sup.3 is CH.sub.3 --, C.sub.2 H.sub.5 -- or CH.sub.3 --, R.sup.4 is CH.sub.3 --CO--, or is H when R.sup.3 is CH.sub.3 -- or C.sub.2 H.sub.5 --, and n is 0 or 2, preferably 0, having a boiling point of 80.degree.-180.degree. C., or in a mixture of these as a solvent. In this process, the riboflavin is obtained in particularly pure form and in very good yields.

Abstract: An improved process for the purification of crude riboflavin which has been prepared by condensation of an N-(D)-ribityl-2-arylazo-4,5-dimethylaniline and barbituric acid or another N-(D)-ribityl-4,5-dimethyl-aniline derivative with a barbituric acid derivative, by dissolving the crude riboflavin in sulfuric acid or phosphoric acid which has been diluted with water and oxidizing the impurities by treating the solution with hydrogen peroxide, or by dissolving the riboflavin in dilute nitric acid at elevated temperature and then isolating the pure riboflavin by precipitation with water, wherein the mineral acid solution of the riboflavin and the oxidizing agent or the solution of the riboflavin in 20 to 70% strength by weight nitric acid is heated extremely rapidly to a temperature at which the solution clearly changes color from greenish to yellow-orange, the solution is kept at this temperature for from 1 to 50, seconds and the oxidation reaction is then interrupted by addition of water.

Abstract: A process for the continuous preparation of isatoic anhydrides by two-stage reaction of an alkali metal phthalamate and/or alkali metal phthalimidate with an alkali metal hypohalite, the first stage being carried out substantially adiabatically and both stages being carried out at high flow rates, wherein phthalimide and/or phthalamic acid is first dissolved in a certain amount of an alkali metal hydroxide solution, the resulting solution is mixed with a hypohalite and reacted at a particular temperature, acid is then added and the reaction is completed at a particular temperature. The compounds obtainable by the process of the invention are valuable starting materials for the preparation of dyes, crop protection agents and scents.