Rapid and solventless chlorination of pyrazoles by ball milling Jia-Xin CHEN , Chi-Min CHEN, Ching Tat TO* Department of Chemistry, Tunghai University, Taiwan Mechanochemical reaction via ball milling utilized the absorption of mechanical energy from friction between grinding ball and reactant in a grinding jar. There are increasing practices of mechanochemistry because of these advantages: (1) solventless (2) room temperature; and (3) enhanced reaction rate and product yield. 1 In this work, various substituted pyrazoles were chlorinated with only slight excess of trichloroisocyanuric acid (TCCA) in a mixer-type ball mill to afford the corresponding 4-chloropyrazoles in good yields. This reaction is aimed to employ no solvent and is carried out at room temperature. Simple filtration workup provided NMR spectroscopically pure products without column chromatography. Gram-scale synthesis is feasible. Mechanistic studies through competition experiments suggested an electrophilic aromatic substitution mechanism.
References 1. Howard, J. L.; Cao, Q.; Browne, D. L. Chem. Sci. 2018 , 9 , 3080-3094.
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