Entry Product R Time (min) Yield (%) Melting Point, °C Found Literature 1 3a 8 96 183-185 183-184[33] 2 3b 15 92 310-312 311-312[33] 3 3c 22 96 213-215 214-215[33] 4 3d 18 91 226-228 227-228[33] 5 3e 24 95 259-261 258-259[33] 6 3f 14 90 291-293 289-290[33] 7 3g 20 93 213-215 214-215[33] 8 3h 30 85 180-182 - 9 3i 20 96 177-179 178 -179[32] 10 3j 28 83 183-185 180-182[32] 11 3k 30 92 186-189 185 -187[32]

Table 3: Synthesis of xanthenes catalyzed by KHSO4-SiO2 from 2-naphthols and aldehydes under ultrasonication.