Quinizarin → Anthraquinone

Participants

Reaction Conditions

Reaction Steps

To a 1 L glass reaction vessel equipped with a mechanical stirrer, temperature probe, water-cooled condenser, and a gas inlet tube was added 2-[2-(3-aminopropoxy)ethoxy]ethanol (291 g), leucoquinizarin (52 g), and quinizarin (152 g). The reaction mixture was heated under a nitrogen atmosphere to 70° C., at which time agitation was started. The reaction mixture was then heated to 80° C. After heating at that temperature for 4 hours, a gentle stream of air was introduced into the reaction mixture and heating at 80° C. was continued with the air sparge in order to oxidize the reaction mixture. After heating an additional 5 hours, the oxidation was complete. The reaction mixture was then cooled to room temperature to produce a blue anthraquinone colorant having a maximum absorbance at 639 nanometers and a color value of 31.5 (absorbance/g/L in methanol). The colorant contained 0.2% 1-(3-(2-(2-hydroxyethoxy)ethoxy)propylamino-4-hydroxyanthraquinone (i.e. violet impurity) and 0.7% of water and methanol insoluble black impurity. The structure of the anthraquinone colorant is shown below:

Provenance & Evidence