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To a solution of S-methyl-I H-pyrazole^-carboxylic acid (2.986 g, 23.68 mmol) in ethanol (20 ml) was added concentrated sulphuric acid (1 ml). The reaction was heated at reflux for 6 hours, cooled to room temperature, and then poured into a saturated aqueous solution of NaHCO3. The mixture was extracted with dichloromethane (3 x 50 ml) then the combined organic extracts dried over MgSO4 and concentrated in vacuo. The product crystallised on standing (2.105 g, 58% yield). MS m/z 155 [MH]+1HNMR (CDCI3): 1.36 (t, 3H), 2.59 (s, 3H), 4.32 (q, 2H), 8.00 (s, 1 H), 9.22 (br s,1 H)
PREPARATION 17Ethyl 3-methyl-1H-pyrazole-4-carboxylate; Sulfuric acid (18 mL, 337.69 mmol) is added to a suspension of 1H-pyrazole-4-carboxylic acid, 3-methyl- (10 g, 79.29 mmol) in ethanol (90 mL) and the mixture is stirred at 85 C. for 20 h. After that time, solvent is partially removed. Residue is basified with 1M sodium hydroxide solution to pH 6-7 and extracted with dichloromethane. Organic layer is decanted, dried over magnesium sulfate and solvent evaporated under reduced pressure to yield 10.3 g of the title compound that is used with no further purification. MS (m/z): 155 (M+1).
Sulfuric acid (18 mL, 337.69 mmol) is added to a suspension of lH-pyrazole- 4-carboxylic acid, 3-methyl- (10 g, 79.29 mmol) in ethanol (90 mL) and the mixture is stirred at 85C for 20 hr. After that time, solvent is partially removed. Residue is basified with 1M sodium hydroxide solution to pH 6-7 and extracted withdichloromethane. Organic layer is decanted, dried over magnesium sulfate and solvent evaporated under reduced pressure to yield 10.3 g of the title compound that is used with no further purification. MS (m/z): 155 (M+l).
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