Sulfuric Acid → 2-(2-Ethyl-phenyl)-2H-pyrazol-3-ylamine

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To a solution (2-Ethyl-phenyl)-hydrazine 1 (35 mmol) and disodium ethylenediaminetetraacetate (20 mg) in methanol (60 ml), 2-chloroacrylonitrile 2 (105 mmol) was added dropwise at 60° C., and the mixture was stirred under reflux for 8 hours. Then concentrated sulfuric acid (94 mmol) was added and the mixture was further heated for 6 hours. After cooling to room temperature the mixture was quenched with anhydrous sodium carbonate (105 mmol) and the solvent was removed under reduced pressure. The residue was treated with water (100 mL) and the product extracted with ethyl acetate (3*100 mL). The combined organic extracts were dried over anhydrous magnesium sulfate and the solvent was removed under reduced pressure. The residue was purified by column chromatography to give (28 mmol) of 2-(2-Ethyl-phenyl)-2H-pyrazol-3-ylamine 3. 1H NMR (300 MHz, CDCl3/TMS) δ 7.44-7.35 (m, 3H), 7.30-7.25 (m, 2H), 5.57 (d, J=2.1 Hz, 1H), 3.57 (br s, 2H), 2.49 (q, J=7.6 Hz, 2H), 1.10 (t, J=7.6 Hz, 3H), 13C NMR (75 MHz, CDCl3/TMS) δ 145.20, 142.60, 139.62, 135.93, 129.47, 129.41, 127.88, 126.55, 88.70, 24.04, 14.34.

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