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Paal-Knorr reaction of aniline and 2,5-diketone; 1-Phenyl-2,5-Dimethylpyrrole

SyntheticPage 553
DOI: 10.1039/SP553
Submitted Apr 04, 2012, published Apr 06, 2012
Christopher Kelly (
A contribution from Leadbeater Group

			Reaction Scheme: <IMG src="/images/empty.gif">Paal-Knorr reaction of <SPAN id=csm1378729432283 class="csm-chemical-name csm-not-validated" title=aniline grpid="1">aniline</SPAN> and 2,5-diketone<IMG src="/images/empty.gif">

Chemicals Used

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%). 

Author's Comments

a.  By this time approximately  one equivalent (based on aniline) of water had condensed into the Dean-Stark trap. 
b. This was judged to be pure by GC-MS and NMR analysis
c. This procedure has been recently used for the undergraduate Advanced Organic Laboratory course at the University of Connecticut with great success. In the case of our students, some obtained red-brown solids while others obtained green ones. Despite these colorations, their GC-MS and NMR data agreed with literature data


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)

Lead Reference

Thiemann, F.; Piehler, T.; Haase, D.; Saak, W.; Lützen A. Eur. J. Org. Chem. 2005, 1991.

Supplementary Information

1H NMR (Adv Org Lab Pyrrole HNMR.jpg)
13C NMR (Adv Org Lab Pyrrole C13NMR.jpg)

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Keywords: Acid Catalysis, aromatics/arenes, Aromatization, Condensation, Cyclization, heterocyclic compounds, Pyrroles

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