The general procedure for the synthesis of 4,6-diaminoresorcinol dihydrochloride from resorcinol was as follows: the reaction was carried out by the one-pot method under the molar ratio of phosphorus pentoxide/methanesulfonic acid/hydroxylamine hydrochloride/acetic acid/resorcinol of 0:4:2:2:1. The specific operation was as follows: first, resorcinol (5.50 g) and acetic acid (6.00 g) were added to a 100 mL three-necked flask, followed by the addition of methanesulfonic acid (13 mL, 0.2 mol), and the reaction system was warmed up to 100 °C after stirring until complete dissolution. Next, hydroxylamine hydrochloride (7.00 g) was slowly added and the reaction was continued at this temperature for 4 hours. Upon completion of the reaction, 6 mol/L hydrochloric acid (40 mL) was added to the system and stirring was continued. The reaction mixture was cooled at 100 °C for 2 h, during which time crystals precipitated. The crystals were collected by filtration, washed sequentially with hydrochloric acid and ethanol, and finally dried under vacuum to afford the target product 4,6-diaminoresorcinol dihydrochloride in 5.0% yield.
