[CH2:1]([C:3]1[N:7]([CH2:8][CH2:9][CH3:10])[N:6]=[C:5]([C:11]#[N:12])[CH:4]=1)[CH3:2].C([O-])(=O)C.[K+].[Br:18]Br.S([O-])(O)=O.[Na+]>C(O)(=O)C>[Br:18][C:4]1[C:5]([C:11]#[N:12])=[N:6][N:7]([CH2:8][CH2:9][CH3:10])[C:3]=1[CH2:1][CH3:2]5-Ethyl-1-propyl-1H-pyrazole-3-carbonitrile (4.89 g, 30.0 mmol) was dissolved in glacial acetic acid (30 mL) and treated with potassium acetate (4.41 g, 44.9 mmol) and bromine (4.79 g, 30.0 mmol). During the slow addition of bromine, an exotherm occurred and ice bath was used to cool the reaction. After the addition of bromine was complete, the reaction was allowed to warm to ambient temperature and stir for 5 hours. Saturated aqueous sodium hydrogensulfite was added to reduce the residual bromine. The mixture was concentrated under reduced pressure and 2 M aqueous sodium carbonate was added to adjust the mixture to pH 9. The mixture was extracted with chloroform (3×100 mL). The organic layers were combined, dried over sodium sulfate, filtered, and concentrated to yield 6.12 g of 4-bromo-5-ethyl-1-propyl-1H-pyrazole-3-carbonitrile as a yellow oil.
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