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 p K a of +3.7.
A library of substituted pyrrole analogs can be quickly produced by using continuous flow chemistry (reaction times of around 8 min.). [10] The advantage of using this method, as opposed to the in-flask synthesis, is that this one does not require the work-up and purification of several intermediates, and could therefore lead to a higher ...
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 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) .
The Rothemund reaction. The Rothemund reaction is a condensation/oxidation process that converts four pyrroles and four aldehydes into a porphyrin. It is based on work by Paul Rothemund, who first reported it in 1936. [1] The method underpins more modern synthesis such as those described by Adler and Longo and by Lindsey.
The direct reaction between phenol and paraformaldehyde is possible via the Casiraghi formylation, [4] but other methods apply masked forms of formaldehyde, in part to limit the formation of phenol formaldehyde resins. Aldehydes are strongly deactivating and as such phenols typically only react once.
Chemical oxidation of pyrrole: n C 4 H 4 NH + 2n FeCl 3 → (C 4 H 2 NH) n + 2n FeCl 2 + 2n HCl. The process is thought to occur via the formation of the pi-radical cation C 4 H 4 NH +. This electrophile attacks the C-2 carbon of an unoxidized molecule of pyrrole to give a dimeric cation [(C 4 H 4 NH) 2] ++. The process repeats itself many times.
The reaction is carried out in the liquid phase in a continuous tube- or tube bundle reactor, which is operated in the cycle gas method. The catalyst is arranged as a fixed-bed and the conversion is carried out in the downflow mode. The product is obtained after multistage purification and separation by extractive and azeotropic distillation. [5]