Imidazole derivatives as redox indicators

Claim 1

An imidazole derivative of the formula ##STR8## wherein R is a hydrogen atom, a tetrahydrofuranyl, cycloloweralkyl or loweralkyl radical, which can be substituted by hydroxyl, loweralkoxy, a sulphuric acid, phosphonic acid or carboxylic acid residue, as well as by a phenyl radical, and R 1 and R 2 , which are different, are julolidine radicals attached at C9, tetrahydroquinoline radicals attached at C6, which optionally carry on the nitrogen atom a loweralkyl radical which, in turn, can be substituted by a sulphuric acid, phosphonic acid or carboxylic acid residue, or radicals of the formula: ##STR9## in which R 4 is a hydroxyl or amino group or a mono- or diloweralkoxylated amino group, in which the loweralkyl radicals can carry a sulphuric acid, phosphonic acid or carboxylic acid residue, and R 3 and R 5 , which can be the same or different, are hydrogen atoms or loweralkyl or loweralkoxy radicals which are optionally substituted by a carboxyl group, with the proviso that R 1 and R 2 cannot simultaneously be julolidine or tetrahydroquinoline and at least one R 4 of the substituents R 1 and R 2 must be a hydroxyl group; or a salt thereof.