Paal-Knorr reaction of aniline and 2,5-diketone; 1-Phenyl-2,5-Dimethylpyrrole
Submitted Apr 04, 2012, published Apr 06, 2012
Aniline (Freshly Distilled, ACS reagent, ≥99.5%, Sigma-Aldrich)
2,5-Hexanedione (≥98%, Sigma-Aldrich)
p-Toluenesulfonic acid • H2O ( ACS reagent, ≥98.5%, Sigma-Aldrich)
Toluene (anhydrous, 99.8%, Sigma-Aldrich)
Sodium sulfate (ACS reagent, ≥99.0%, anhydrous, granular, Sigma-Aldrich)
Saturated sodium bicarbonate solution
Saturated sodium chloride solution
To a 250 mL one-necked round bottom flask equipped with stir bar was added aniline (2.79 g, 0.030 mol), 2,5-Hexanedione (3.65 g, 0.032 mol), and toluene (75 mL, 0.4 M in aniline). Upon mixing for 5 minutes, p-TsOH (0.114 g, 0.0006 mol) was added all at once. The flask was then equipped with a Dean-Stark trap and reflux condenser. The solution was heated to reflux (≈120 oC). for 1 houra. After this time the flask was cooled to room temperature and the solution was transferred to a 500 mL separatory funnel. The organic layer was washed with a saturated sodium bicarbonate solution (2 X 100 mL), deionized water (2 X 100 mL), and finally with brine (2 X 100 mL). The organic layer was dried with Na2SO4 and the solvent was removed by rotary evaporation to afford a greenish solidb,c (3.69 g, 72%).
1H NMR (CDCl3, 300 MHz) δ ppm 2.03 (s, 3 H) 5.91 (s, 2 H) 7.19-7.22-(m, 2 H) 7.38-7.47 (m, 3 H) 7.37 (d, J=8.80 Hz, 2 H) 13C NMR (CDCl3, 75 MHz) δ ppm 13.12 (CH3) 105.82 (CH) 127.72 (C) 128.36 (CH) 128.83 (CH) 129.15 (CH) 139.15 (C)
Thiemann, F.; Piehler, T.; Haase, D.; Saak, W.; Lützen A. Eur. J. Org. Chem. 2005, 1991.
1H NMR (Adv Org Lab Pyrrole HNMR.jpg)
13C NMR (Adv Org Lab Pyrrole C13NMR.jpg)
Keywords: Acid Catalysis, aromatics/arenes, Aromatization, Condensation, Cyclization, heterocyclic compounds, Pyrroles