Search results
Results from the WOW.Com Content Network
Pyrrole is an extremely weak base for an amine, with a conjugate acid pK a of −3.8. The most thermodynamically stable pyrrolium cation (C 4 H 6 N +) is formed by protonation at the 2 position. Substitution of pyrrole with alkyl substituents provides a more basic molecule—for example, tetramethylpyrrole has a conjugate acid pK a of +3.7.
The Knorr pyrrole synthesis is a widely used chemical reaction that synthesizes substituted pyrroles (3). [1] [2] [3] The method involves the reaction of an α-amino-ketone (1) and a compound containing an electron-withdrawing group (e.g. an ester as shown) α to a carbonyl group (2). [4] The Knorr pyrrole synthesis
Below is one published mechanism for the reaction: [5] Mechanism for the Hantzsch Pyrrole Synthesis. The mechanism starts with the amine (1) attacking the β carbon of the β-ketoesters (2), and eventually forming an enamine (3). The enamine then attacks the carbonyl carbon of the α-haloketone (4). This is followed by the loss of H 2 O, giving ...
The amine attacks the other carbonyl to form a 2,5-dihydroxytetrahydropyrrole derivative which undergoes dehydration to give the corresponding substituted pyrrole. [7] Paal–Knorr pyrrole synthesis mechanism. The reaction is typically run under protic or Lewis acidic conditions, with a primary amine.
The condensation reaction can be shown below: After the condensation, the pyrrole formation can proceed as normal. The Trofimov reaction can produce both N-H and N-vinyl pyrroles depending on the reaction conditions used. The N-vinyl pyrrole can be formed by the deprotonation of the pyrrole nitrogen which then attacks a second acetylene molecule.
The aldehyde and pyrrole are heated in this medium to afford modest yields of the meso tetrasubstituted porphyrins [RCC 4 H 2 N] 4 H 2. The reaction entails both condensation of the aldehydes with the 2,5-positions of the pyrrole but also oxidative dehydrogenation of the porphyrinogen [RCC 4 H 2 NH] 4.
Pyrrolines, also known under the name dihydropyrroles, are three different heterocyclic organic chemical compounds that differ in the position of the double bond.Pyrrolines are formally derived from the aromate pyrrole by hydrogenation. 1-Pyrroline is a cyclic imine, whereas 2-pyrroline and 3-pyrroline are cyclic amines.
Naphthoylpyrroles: Any compound containing a 3-(1-naphthoyl)pyrrole structure with substitution at the nitrogen atom of the pyrrole ring by an alkyl, haloalkyl, alkenyl, cycloalkylmethyl, cycloalkylethyl, 1-(N-methyl-2-piperidinyl)methyl, or 2-(4-morpholinyl)ethyl group whether or not further substituted in the pyrrole ring to any extent and ...