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

Abstract 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. ZnCl 2 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 ZnCl 2 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 N 2 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 ZnCl 2 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.