disodium 4,4'-[methylenebis(4,1-phenyleneimino)]bis[1-amino-9,10-dihydro-9,10-dioxoanthracene-2-sulphonate]

Sodium 1-amino-4-bromo-9,10-dioxo-9,10-dihydroanthracene-2-sulfonate (0.081 g, 0.20 mmol) and 4,4 ′-methylenedianiline (0.20 mmol) were added to a 5 mL microwave reaction flask equipped with a magnetic stirring bar, followed by a Na2HPO4 (pH 9.6) (4 mL) and a NaH2PO4 (pH 4.2) (1 mL) in buffer solution. A catalytic amount (~0.002-0.003 g) of finely powdered elemental copper was added. The mixture was covered and irradiated in a microwave oven at 80°C for 20 minutes. The reaction mixture was then cooled to room temperature and diluted with methanol. The solution was filtered to remove the copper powder. The solvent was evaporated and the residue was purified by fast reversed-phase column chromatography using RP-18 silica gel (water as eluent) to give acid blue 2RW.