Table 4 Comparison the efficiency of the Co₃O₄@SiO₂/OS-SO₃H nanocatalyst with that of formerly reported catalytic systems in the synthesis of tetrahydrobenzo[a]xanthen-11-ones.

1

NH₂SO₃H

[BMIM]BF₄, 80 °C

4

60

85

⁶⁶

2

Fe₃O₄@nano-walnut shell/B^III (FNWSB)

Solvent-free, 80 °C

4

40

92

⁶⁷

3

Fe₃O₄@chitosan

EtOH, 40 °C

4

180

90

⁶⁸

4

Cu/Fe₃O₄@APTMS-DFX

Solvent-free, 120 °C

5

45

90

⁶⁹

5

KF/CP NPs

Solvent-free, 80 °C

4

60

91

⁷⁰

6

Co₃O₄@SiO₂/OS-SO₃H

EtOH, 60 °C

7

40

95

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