General procedure for the synthesis of 2,5-dichloroterephthalic acid from 2,5-dichloro-p-xylene: 5 g (0.028 mol) of 2,5-dichloroterephthalic acid, 26 g (0.165 mol) of potassium permanganate, 80 mL of pyridine, and 20 mL of deionized water were added to a 250 mL round-bottom flask. The reaction mixture was heated to 100 °C and stirred for 12 hours. The brown manganese oxide was removed by filtration while hot and the brown solid was subsequently re-slurried twice with 100 mL of deionized water. The filtrates were combined and the solvent was removed by distillation under reduced pressure. The resulting pale yellow syrupy liquid was acidified with hydrochloric acid to pH=1. The white solid was collected by filtration through a glass sand-core funnel and dried in a vacuum oven at 50°C overnight. Yield: 53-87%.
General procedure for the synthesis of 2,5-di-(p-toluic acid)-terephthalic acid: a three-necked round-bottomed flask equipped with an argon inlet and a magnetic stirrer was charged with 23.19 g (0.216 mol) of p-toluidine, 3.6 g (0.014 mol) of 2,5-dichloroterephthalic acid, 4.6 g (0.033 mol) of anhydrous K2CO3, 0.060 g ( 0.00033 mol) anhydrous copper(II) acetate, 0.750 g (0.0045 mol) potassium iodide, 16.8 g (0.271 mol) ethylene glycol and 3.8 g (0.211 mol) deionized water. The mixture was heated to 130 °C and maintained for 12 hours under argon protection. After the reaction was completed, it was cooled to room temperature and diluted with 50 mL of deionized water. Hydrochloric acid was added with stirring to adjust the pH to 1. A dark colored solid was obtained by filtration through a glass sand core funnel. The solid was dissolved in a pH 7 solution containing 3 mL of ammonium hydroxide and 250 mL of deionized water and filtered to remove undissolved solid. The resulting yellow-green solution was acidified with acetic acid to pH=3. After acidification, a dark brown solid was formed, filtered through a glass sand-core funnel, and dried in a vacuum oven at 100°C overnight. Yield: 31%.
General procedure for the synthesis of quinacridone PR122 nanoparticles: 15 g of polyphosphoric acid and 1 g of 2,5-di-(p-tolylamino)-terephthalic acid powder were added to a 250 mL round-bottomed flask fitted with a magnetic stirring bar. The mixture was heated to 160 °C and maintained for 2 h. A deep purple-red color appeared during the reaction. After completion of the reaction, it was cooled to room temperature and diluted with 80 mL of concentrated sulfuric acid. The resulting solution was transferred to a dropping funnel and slowly added dropwise under stirring to a resin kettle containing 100 mL of N-methyl-2-pyrrolidone and 1.96 g (0.002 mol) of SPAN 85, and the temperature was controlled to be below 45 °C during the dropwise addition. After dropwise addition, stirring was continued at room temperature for 30 min, followed by filtration through a glass sand core funnel. The resulting solid was re-slurried sequentially with 300 mL of isopropanol and 300 mL of deionized water, each time filtered through a glass sand core funnel. Finally, the product was freeze-dried for 48 hours. Yield: 50% (D50 = 100 ± 1.4 nm, GSD = 1.71 ± 0.04). Transmission electron microscopy observations showed that the particle morphology was that of thin circular flakes of regular shape with a size range of about 50 to 100 nm.
