A process for the manufacture of mixtures of
fluoran compounds by the reaction of keto acids of formula (II) with a compound of formula (III) in the presence of a dehydrating condensation agent, wherein R1 and R2 independently represent
hydrogen; an
alkyl of 1-18 carbon, a secondary
alkyl with respect to the
carbon atom bonded to the
nitrogen atom of 3-13 carbon atoms, a cycloalkyl of 4-8 carbon atoms or a phenyl, both of which may be substituted by at least one substituted selected from the group consisting of
halogen atoms and alkyls having 1-4 carbon atoms, an aralkyl of 7-10 carbon atoms; or R1 and R2, together with the adjacent
nitrogen atom from a heterocyclic ring; R3 is
hydrogen, an
alkyl of 1-4 carbon atoms, an alkoxy of 1-4 carbon atoms, a phenyl; a substituted phenyl or a
halogen; R4 is an alkyl group of 1-18 carbon atoms, a carboxyalkyl of 1-18 carbon atoms, a carboxycycloalkyl of 4-8 carbon atoms, an alkylamino of 1-18 carbon atoms, a cycloalkylamino of 4-8 carbon atoms, a dialkylamino or dicycloalkylamino; an arylamino, a substituted arylamino; an aralkylamino of 7-10 carbon atoms; a diaralkylamino; R5 is an alkyl of 1-18 carbon atoms, a carboxy alkyl of 1-18 carbon atoms or a
halogen and R6 is
hydrogen or alkyl of 1-4 carbon atoms.