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20th November 2011 @ 04:11
Paal Knorr Synthesis of 2,5-dimethyl-1H-phenyl-pyrrole



2,5-hexanedione (7 mL, 59.7 mmols, 1 equiv.) and aniline (6 mL, 65.6 mmols, 1.1 equiv.) were mixed and heated in an oil bath at 80 °C. After 5 hrs, TLC and NMR peak ratios (hexanedione methyl: product methyl) showed reaction complete. The reaction was removed from the heat source and allowed to cool in a refrigerator overnight. The brown crystalline solid was dissolved in EtOH (32 mL) and heated gently. Solution was then cooled in ice, with precipitation of fine crystals observed. Solution was filtered and the filter cake was washed with citric acid (3 × 10 mL) and water (10 mL) to give a final product with a wet weight of 9.16 g. Product dried was overnight under vacuum to give a red brown fine grain substance (6.2 g, 60.4%).

Collected data: 2,5-dimethyl-1H-phenyl-pyrrole

mpt: 49-51oC
1H-NMR (300 MHz, CDCl3): δ 7.36-7.44 (sx, 3H), 7.17-7.21 (t, 2H), 5.90 (s, 2H), 2.02 (s, 6H)
13C-NMR (75 MHz, CDCl3): δ 139.11, 129.12. 128.83, 128.34, 127.70, 105.76, 13.10
m/z (APCI+): 173 [M+H]+, 100%
IR: 645.64, 695.38, 716.51, 746.80, 773.05, 1005.67, 1037.06, 1318.40, 1401.16, 1493.91, 1519.99, 1596.99

For data files, refer to Paal-Knorr Synthesis of 2,5-dimethyl-1-phenyl-1-H-pyrrole (LMW 1-2)

References:
DOI: 10.1002/cmdc.200600026
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