2-phenylbenzimidazole-5-sulphonic acid from isolated 3,4-diaminobenzenesulphonic acid and use thereof in cosmetic preparations
AssigneeBayer Aktiengesellschaft
InventorsGünter Rauchschwalbe, Herbert Emde, Wolfram Kissener, Klaus-Christian Paetz
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Abstract
A process for the preparation of 2-phenylbenzimidazole-5-sulphonic acid, characterized in that 3,4-diaminobenzenesulphonic acid is reacted at a pH between 4 and 7 in aqueous solution with 0.9 to 1.5 mol of benzaldehyde per mole of 3,4-diaminobenzenesulphonic acid and with 1.0 to 3.0 mol of SO2 per mole of 3,4-diaminobenzenesulphonic acid, or an agent which comprises 1.0 to 3.0 mol of SO2 per mole of 3.4-diaminobenzenesulphonic acid, is described.
Claims6
Process for the preparation of 2-phenylbenzimidazole-5-sulphonic acid, comprising reacting 3,4-diaminobenzenesulphonic acid at a pH between 4 and 7 in aqueous solution with 0.9 to 1.5 mol of benzaldehyde per mole of 3,4-diaminobenzenesulphonic acid and with 1.0 to 3.0 mol of SO2 per mole of 3,4-diaminobenzenesulphonic acid, or an agent which comprises 1.0 to 3.0 mol of SO2 per mole of 3.4-diaminobenzenesulphonic acid, wherein the agent is alkali metal salts selected from the group consisting of Na2HSO3, Na2S2O5 and Na2SO3.
Dependencies are inferred from the claim text.