Essay on The Knorr Synthesis of Pyrroles

Essay on The Knorr Synthesis of Pyrroles

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The Knorr Synthesis of Pyrroles

A mixture of ethyl acetoacetate 1 (7.52 g, 7.5 mL) in glacial acetic acid (18 mL) was prepared and cooled to 5oC while stirring. Sodium nitrate solution (2.1 g in 5 mL deionised water) was added at such a rate that the temperature of reaction did not exceed 7oC. Once this addition was complete the mixture was stirred with cooling for 10 minutes before being allowed to warm to room temperature.
Zinc dust (4.0 g) was added to the reaction mixture in small portions so that the mixture refluxed gently, the reaction mixture was then heated to reflux for one hour.
The mixture was then allows to cool and the excess zinc to settle. While still hot the solution was decanted into stirred cold water (200 mL) precipitating the crude product. The zinc residue was washed with warm glacial acetic acid (2 x 5 mL) and this was added to the aqueous solution.
This suspension was allowed to stand for 10 minutes, before being filtered, washed (water 2 x 10 mL) and air dried. The crude product was recrystallised from ethanol to yield a yellow solid 3. 26% yield (1.83 g); Elemental analysis for C12H17NO4: C: 54.918%, H: 6.704%, N: 5.122% (Theoretical: C: 60.24%, H: 7.16%, N: 5.85%, Loss:26.75%); Mr 239.2 g mol-1; ν/cm-1: 1259.48 (N-C), 1667.41 (C=C), 1688.41 (C=O), 2976.58 (C-H), 3265.02 (N-H); 1H-NMR (400 MHz, CDCl3), δ/ppm: 1.24 and 1.38 (dt, 3H, C-CH3, C12 and C15), 2.51 and 2.56 (ds, 6H, 2 x =C-CH3, C6 and C7), 4.31 (m, 4H, 2 x -CH2-, C11 and C14), 5.3 (s, 1H, N5-H); 13C-{1H}-NMR (400 MHz, CDCl3), δ/cm-1:11.98 (C6 and C7), 14.43 (C12 and C15), 59.50 and 60.29 (C11 and C14), 133.5 (C3), 117.5 (C1), 131.3 (C2), 138.6 (C4), 165.47 (C8 and C9) .

Results and Discussion
Product 3 was formed i...

... middle of paper ...

...nal peaks in the spectrum are at much higher wavenumbers because of the lighter elements involved. The C-H stretch is at 2976.58 cm-1 and the N-H stretch is at 3265.02 cm-1. These peaks all correspond well with the literature values2.

Product 3 was isolated in a low yield of 27% and with some solvent impurities as shown by the analytical techniques but it was indeed synthesised successfully.
On repeating this experiment more care should be taken when purifying to remove the solvent impurities and minimise loss of crude product.

1. H. E. Gottleib, V. Kotlyar and A. Nudelman, J. Org. Chem., 1997, 62, 7512.

2. E. Fabiano and B. T. Golding, J. Chem. Soc. Perkin Trans., 1991, 3371.

Appendix 1

Figure 2 1H-NMR spectrum of product 3.

Figure 3 13C-NMR spectrum of product 3.

Figure 4 IR spectrum of product 3.

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