Washing agents contg pH colour indicator - to indicate the pH range over which the surface active agent loses its cleaning capacity

摘要

Cleaning agents contain an anionic, non-ionic, cationic or amphoteric surface active agent combined with a pH indicator which indicates the pH range over which the surface active agent loses its cleaning capacity. The indicator used may be e.g. phthalein indicators, sulphone phthalein indicators, azo indicators, etc. Prefd. indicator for domestic washing agents is of the type thymol (carboxyl) phthalein, made by condensing 2,5-dialkyl phenols with trimellitic anhydride in the presence of a Friedel Crafts catalyst. Such indicators give a blue colour at pH 9.7 and turn colourless suddenly at pH 8.8.