Preparation of water-soluble food-grade triphenylmethane colors

摘要

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 C2-C4-alkanol, urea, a urea derivative or a mixture thereof, at a potential epsilon h