4-aminobenzoic acid (ABA) (0.2 g) and 3,5-dimethylaniline (DMA) (0.3 g) as the starting product is solubilized in HBF 4 acid (1.8 mL for ABA and 2 mL for DMA). The mixture was kept under stirring for 15 min. After cooling the solutions to 0 °C with ice, the solution of sodium nitrite NaNO 2 (0.194 g for ABA and 0.207 g for DMA) as an oxidant is dissolved in a minimum of water was added dropwise to the reaction mixture and the reaction was obtained for 30 min at 0 °C. After stirring for 30 minutes, the final product is washed with cold diethyl ether, after several washes under vacuum, a precipitate appears. The synthesized diazonium salts 4-carboxybenzenediazonium (AB) and 3-5 dimethyl diazenylbenzoic (DMB) were stored in the freezer.