Sulfuric Acid → 1-(5-Methyl-1,2-oxazol-3-yl)ethan-1-one
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N(OCC)=O.[N:6]([O-:8])=O.[Na+].S(=O)(=O)(O)O.[CH3:15][C:16](=O)[CH2:17][CH2:18][C:19](=[O:21])[CH3:20]>C(O)C.O.Cl.CCOCC>[CH3:15][C:16]1[O:8][N:6]=[C:18]([C:19](=[O:21])[CH3:20])[CH:17]=1N(OCC)=O.[N:6]([O-:8])=O.[Na+].S(=O)(=O)(O)O.[CH3:15][C:16](=O)[CH2:17][CH2:18][C:19](=[O:21])[CH3:20]>C(O)C.O.Cl.CCOCC>[CH3:15][C:16]1[O:8][N:6]=[C:18]([C:19](=[O:21])[CH3:20])[CH:17]=1
Ethyl nitrite gas was generated in situ by addition of a solution of sodium nitrite (100 g, 1.44 mol) in 50 mL of ethanol and 400 mL of water dropwise into a solution of 50 mL of concentrated sulfuric acid in 50 mL of ethanol and 400 mL of water in a stand-alone reaction vessel. The ethyl nitrite gas generated was bubbled into another reaction flask containing a mixture of hexane-2,5-dione (80 g, 700.88 mmol) in concentrated hydrochloric acid (10 mL). The resulting solution was stirred for 6 hr at 50° C. After cooling to room temperature, the reaction mixture was diluted with ether (600 mL) then washed with of saturated sodium carbonate solution (2×500 mL) and brine (500 mL). The organic layer was dried with anhydrous sodium sulphate then concentrated in vacuo. The crude product was purified by distillation under reduced pressure (12 mm Hg) and the fraction with the boiling point of 70° C. was collected to give 61 g (69%) of the title compound as a colorless liquid: 1H NMR (300 MHz, CDCl3) delta 6.36 (s, 1H), 2.63 (s, 3H), 2.49 (s, 3H).
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