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20th November 2011 @ 05:20
Paal Knorr synthesis of 2,5-dimethyl-1H-(p-tolyl)- pyrrole



p-toluidine (7.033 g, 65.6 mmols, 1.1 equiv.) and 2,5-hexanedione (7 mL, 59.7 mmols, 1 equiv.) were heated in an oil bath at 80 °C. TLC at 4 hrs 25 mins showed reaction complete and reaction mixture was removed from the heat source and allowed to cool to room temperature. Product was then extracted with EtOAc (20 mL) and washed with 10% citric acid (3 × 20mL) and brine (20mL). Solution was dried with MgSO4 and activated charcoal added to remove coloured impurities. Solution was stirred for 60 minutes and then filtered and washed with EtOAc. Filtrate was then concentrated under reduced pressure and cooled in a refrigerator overnight. The brown crystalline solid was dissolved in EtOH (20 mL) and heated gently. Solution was then cooled in ice, with precipitation of fine crystals observed. Solution was filtered and the filter cake washed with water (3 × 10 mL) to form a paste with a wet weight of 14.8 g. Product was dried overnight under vacuum to form an ochre-coloured fine grain substance (8.3 g, 74.5%).

Collected data:2,5-dimethyl-1H-(p-tolyl)- pyrrole

mpt: 45-46 °C
1H-NMR (300 MHz, CDCl3): δ 7.20-7.23 (qr, 2H), 7.05-7.08 (qn, 2H), 5.88 (s, 2H), 2.38 (d, 3H), 2.01 (d, 6H)
13C-NMR (75 MHz, CDCl3): δ 137.53, 136.55, 129.82, 128.89, 128.13, 105.67, 21.26, 13.15
m/z (APCI+): 187 [M+H]+, 100%
IR: 750.03, 826.40, 995.02, 1034.4, 1104.72, 1319.51, 1403.30, 1513.22, 2919.24, 3673.73, 3709.99, 3734.55

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

References:
doi: 10.1021/ja9041093
doi: 10.1002/cmdc.200600026
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