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Heterocyclic Chemistry: The Knorr Synthesis of Pyrroles Essay

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The Knorr synthesis of the pyrrole, 2,4-diethoxycarbonyl-3,5-dimethylpyrrole, was achieved using an α-amino ketone, ethyl acetoaminoacetate and reacting it with its predecesso r, ethyl acetoacetate in a double condensation reaction . The product was analysed by 1H NMR, 13C NMR, mass spectrometry and IR spectroscopy giving positive results .
Introduction
Pyrrole has been a molecule of great interest due to its heterocyclic aromatic properties. The lone pair on the nitrogen is delocalised within the ring, causing the heterocycle to be electron-rich . This causes the ring to become increasingly nucleophilic, and therefore makes it susceptible to attack from electrophiles . The addition of these new substitutions makes more important molecules , which have a huge contribution to not only the chemical industry, but also the biological. 1 Substituted pyrrole molecules are fantastic precursors to make complex molecules, such as medicines, agrochemicals and dyes. Indole, an important benzo-pyrrole, is the basis of the important protein, tryptophan and has functions as a neurotransmitter in the brain. The neurotransmitter, serotonin, is important in making modern drugs such as sumatriptan which treats migraines.2

Pyrrole synthesis can be achieved by a vast number of methods. Some of the most common processes used in today’s laboratory include the Hantzch pyrrole method, Paal-Knoor Knorr synthesis and the Knoorr synthesis; the latter which will be studied in this experiment. Other complex methods explored include Robinson’s utilization of the reaction between an aldehyde and a hydrazine . However, this method requires high temperatures which are not economically favourable to maintain and so the other classic methods are gene...


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...ential of the reaction and products.

References



Works Cited
1. V. Amarnath, D. C. Anthony, K. Amarnath, W. M. Valentine, L. A. Wetterau, D. G. J. Org. Chem. 1991, 56, p. 6924-6931.
2. J. Clayden, N. Greeves, S. Warren, P. Wothers. Organic Chemistry. 8th ed. 2007, Oxford University Press, p. 1186-1191.
3. G. M. Robinson, R. Robinson. J. Chem. Soc. 1918, p. 639-645.
4. A. H. Corwin. Heterocyclic Compounds. 1950, 1, p. 287.
5. Y. Byun, D. A. Lightner. J. Heterocyclic Chem. 1991, 28. p. 1683-1692.
6. Professor Chris Willis, School of Chemistry, University of Bristol
7. Professor Kevin Booker-Milburn, 2nd Year Heterocyclic notes, School of Chemistry, University of Bristol
8. H. Fischer. Organic Syntheses Coll. 1943, 2, p. 202; H. Fischer. Organic Syntheses Coll. 1935, 15, p. 17.
9. C. Schmuck, D. Rupprecht. Synthesis 2007, 2007, 20, p. 3095-3110.


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