Effect of the Co(II)@AC catalyst with the activated carbon modified by zinc chloride as a carrier on the synthesis of 1-(4-chlorophenyl)-1H-pyrazol-3-ol from the oxidation of 1-(4-chlorophenyl)-pyrazolidin-3-one by oxygen

The oxidation of 1-(4-chlorophenyl)-pyrazolidin-3-one to 1-(4-chlorophenyl)-1H- pyrazol-3-ol by air can be accelerated by the Co(II)@AC catalyst prepared by loading Co(II) on activated carbon with wet impregnation method. ZnCl₂ solution has been used to treat activated carbon to ameliorate the catalytic ability of Co(II)@AC catalyst. The experiments indicate that the optimal catalyst is made by immersing activated carbon in 0.7 mol/L ZnCl₂ solution at 50°C for 6 h with a liquid/solid ratio of 30/1 (mL/g) followed being calcined at 700°C for 5 h at a heating rate of 5°C/min under N₂ protection. The 1-(4-chlorophenyl)-1H-pyrazol-3-ol concentration catalyzed by the catalyst loaded on the best carbon reaches 0.01953 kg/L, which is 27.56% higher than that catalyzed by the catalyst loaded on the original carbon. The characterization results manifest that the modification with ZnCl₂ enriches the porous structure and increases the acidic groups on the surface of activated carbon. The conversion of 1-(4-chlorophenyl)-pyrazolidin-3-one is mainly determined by the physical structure of the activated carbon while the selectivity to 1-(4-chlorophenyl)-1H- pyrazol-3-ol is largely affected by the chemical characteristics of the activated carbon.