General method: 3,4-dichlorobenzyl alcohol (1 mmol) was dissolved in 2 mL of toluene and graphene oxide (GO, 0.3 g) was added. The mixture was placed in an Elmasonic P ultrasonic cleaning device and sonicated at 37 kHz frequency and 100% output power at 80 °C for the time shown in Table 4. Subsequently, Oxone (1 mmol) and 2 mL of methanol were added. The mixture was irradiated in the reaction medium for the time shown in Table 4. After completion of the reaction, the mixture was filtered through a sintered funnel, concentrated under reduced pressure and extracted with ethyl acetate. The organic layer was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The product was purified by column chromatography with hexane/ethyl acetate (100:3) as eluent. The spectral data of the resulting methyl 3,4-dichlorobenzoate were in agreement with those reported in the literature [5,40,42,43]. Spectral data of methyl 3,4-dichlorobenzoate (entry 9, Table 4): light yellow solid, melting point 44.7 °C; IR (KBr) ν= 3089, 3022, 2958, 1729, 1589, 1435, 1378, 1301, 1110, 757 cm-1; 1H NMR (300 MHz, CDCl3) δ= 3.94 (s 3H, OCH3), 7.53 (d, J = 8.3 Hz, 1H, Ar-H), 7.87 (dd, J = 8.3, 1.9 Hz, 1H, Ar-H), 8.13 (d, J = 1.9 Hz, 1H, Ar-H); 13C NMR (75 MHz, CDCl3) δ = 52.54, 128.63, 129.94, 130.52, 131.53, 132.92, 137.56, 165.21; MS (EI, 70 eV) m/z (relative abundance): 208 (5) [M+4]+, 206 (31) [M+2]+, 204 (50) [M]+, 177 (10), 175 (62), 173 (100), 145 (30), 109 (20), 74 (18).
