108 Questions
What type of reagents are required for the halogenation of pyrroles?
Mild reagents
What is the product of the reaction of pyrrole with bromine in carbon tetrachloride?
3-Bromopyrrole
What is the position of the substituent in pyrrole that undergoes iodination?
Position-2
What is the role of N-halosuccinimides in the preparation of 2-bromo and 2-chloropyrrole?
They are used to directly prepare the compounds
What is the reason for the high reactivity of pyrrole ring system?
Due to the presence of a heteroatom
What is the result of the reaction of pyrrole with bromine in carbon tetrachloride?
Monobromination of pyrrole
What is the reactant that provides N-acylpyrrole in the given reaction?
Pyrrole
What is the condition required for the bromination of pyrrole?
Low temperature and pressure
What is the temperature at which the reaction between pyrrole and acetic anhydride takes place?
200°C
What is the effect of electron-withdrawing substituent on the pyrrole ring system?
It increases the reactivity of the ring system
What is the role of sodium acetate in the reaction?
Presence
What is the percentage of 2-acytal pyrrole formed in the reaction?
90%
What is the byproduct of the reaction?
CH3COOH
What is the other product formed in the reaction besides N-acylpyrrole?
Acetic acid
What is the general method of synthesizing substituted pyrroles?
Cyclization of 1,4-diketones in combination with ammonia or amines
What is the driving force of the reaction in the Paal-Knorr synthesis?
The formation of a stable aromatic system
What is the product of the reaction between acetylene and ammonia over red hot tube?
Pyrrole
What is the role of zinc dust in the synthesis of pyrrole?
It is used for distillation
What is the byproduct of the reaction between 1,4-diketones and ammonia or amines?
Water
What is the purpose of reflux in the Paal-Knorr synthesis?
To heat the reaction mixture
What is the product of the reaction between furan, ammonia, and steam over alumina catalyst?
Pyrrole
What is the advantage of the Paal-Knorr synthesis?
It produces a stable aromatic system
What is the result of the reaction of alkali metal salt of pyrroles with an acyl halide?
N-Acylpyrroles
What is the name of the reaction that produces 2-Formylpyrrole?
Vilsmeier reaction
What is the problem with Friedel-Crafts alkylation of pyrrole?
It is not possible to obtain monoalkylated product
What is used as a reagent in the Vilsmeier reaction?
POCI3 and N, N-dimethylformamide
What type of halides can be used in Friedel-Crafts alkylation of pyrrole?
Alkyl, allyl- and benzyl halides
What is the product of the reaction between alkali metal salt of pyrroles and an acyl halide?
N-Acylpyrroles
What is the product of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
2-alkylpyrrole
What is the condition required for the diazo coupling reaction of pyrrole with benzenediazonium salts?
Alkaline media
What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?
Pyrrolyl anion
What is the product of the diazo coupling reaction of pyrrole with benzenediazonium salts?
2,5-bis(aza)-pyrrole
What is the reagent used in the Friedel-Crafts alkylation of pyrrole?
Grignard reagent
At what temperature does the Friedel-Crafts alkylation of pyrrole with a Grignard reagent take place?
100°C
What is the byproduct of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
Complex mixture
What is the type of rearrangement involved in the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
Hofmann-Martius rearrangement
What is the reaction that occurs when pyrrole reacts with CHCl3 and strong alkali?
Riemer Tiemann reaction
What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?
Carbine
What is the product of the reaction between alkali metal salt of pyrroles and an acyl halide?
N-Acylpyrrole
What is the purpose of reflux in the Paal-Knorr synthesis?
To drive the reaction forward
What is the yield of the corresponding pyrrole-2-sulfonic acid obtained when pyrrole reacts with pyridine-sulfur trioxide complex at 100°C?
90%
What is the role of zinc dust in the synthesis of pyrrole?
To reduce the reaction mixture
What is the main product formed when pyrrole reacts with acetic anhydride at 200°C?
2-Acetylpyrrole
What is the product of the reaction between furan, ammonia, and steam over alumina catalyst?
Pyridine
What is required for the sulfonation of pyrroles substituted with electron-withdrawing substituents?
Vigorous reaction conditions
What is the result of the reaction of pyrrole with bromine in carbon tetrachloride?
2-Bromopyrrole
What is the driving force of the reaction in the Paal-Knorr synthesis?
Heat
How can N-Acetylpyrrole be obtained in high yield?
By heating pyrrole with N-acetylimidazole
What is the role of pyridine in the sulfonation of pyrrole?
It forms a complex with sulfur trioxide
What is the byproduct formed in the direct acetylation of pyrrole with acetic anhydride?
3-Acetylpyrrole
Why is pyrrole more reactive than benzene?
Because of the resonance that pushes the electrons from the N-atom into the ring
What happens when pyrrole reacts with strong acids?
It forms a pyrrole trimer
What is the difference between the reactivity of pyrrole and benzene?
Pyrrole is more reactive than benzene
What type of reaction is involved in the acylation of pyrrole?
Acylation
Why are modified reagents used in the electrophilic substitution of pyrrole?
To avoid the use of strong acids that induce polymerization
What is the result of the reaction of pyrrole with isocyanate?
Formation of a phenyl isocyanate
Why is pyrrole sensitive to strong acids?
Due to the protonation that occurs at one of C-3
What is the characteristic of pyrrole that resembles the most reactive benzene derivatives?
Electron-rich c-atoms in the ring
What is the product of the reaction between pyrrole and acetic anhydride in the presence of sodium acetate?
N-acylpyrrole
What is the ratio of 2-acytal pyrrole to 3-acytal pyrrole in the given reaction?
90:10
What is the reagent that provides N-acylpyrrole in the given reaction?
Acetic anhydride
At what temperature does the reaction between pyrrole and acetic anhydride take place?
200°C
What is the role of sodium acetate in the reaction?
Base
What is the byproduct of the reaction between pyrrole and acetic anhydride?
CH3COOH
What is the major product of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
2-Alkylpyrrole
What is the condition required for the diazo coupling reaction of pyrrole with benzenediazonium salts?
Alkaline media
What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?
Pyrrolyl anion
What is the product of the diazo coupling reaction of pyrrole with benzenediazonium salts?
2,5-Bis(aza)-pyrrole
What type of rearrangement is involved in the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
Hofmann-Martius rearrangement
What is the temperature at which the Friedel-Crafts alkylation of pyrrole with a Grignard reagent takes place?
100°C
What is the byproduct of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?
Complex mixture
What is the purpose of using a Grignard reagent in the Friedel-Crafts alkylation of pyrrole?
To introduce an alkyl group at the 2-position
Pyrrole reacts with CHCl3 and strong alkali to form two types of products.
True
Diazo coupling occurs at the A position if both the X-positions are occupied.
False
Ring opening reaction occurs in the presence of NH,OH / EtOH under reflux conditions.
True
Oxidation reaction occurs in the presence of CrO3 / CH3COOH.
True
Reduction reaction occurs in the presence of Zn / CH3COOH.
True
The Riemer-Tiemann reaction is a type of formylation reaction.
True
Pyrrole resembles phenol in its chemical properties.
True
Carbine insertion reaction occurs in the reaction of pyrrole with CHCl3 and strong alkali.
True
Pyrrole is a strong base because the lone pair of electron of the nitrogen atom contributes to the aromaticity.
False
The Knorr-pyrrole synthesis involves the condensation of a-amino ketones with a f-diketone or a B-ketoester to give a substituted pyrrole.
True
Pyrrole is synthesized by the reaction of furan, ammonia, and steam over palladium catalyst.
False
The Paal-Knorr synthesis involves the cyclization of 1,4-diketones in combination with ammonia (NH3) or amines.
True
Pyrrole exhibits strong acidic properties due to participation of N lone pair in aromaticity.
False
Pyrrole can be obtained by distillation of succinimide over copper dust.
False
Pyrrole reacts with sodium amide in liquid ammonia to give a salt-like compound that can be used to alkylate or acylate the nitrogen atom.
True
The Paal-Knorr synthesis yields a non-aromatic system.
False
Hantzsch synthesis for pyrrole involves the condensation of halo ketone, B-keto ester and primary amine.
True
Pyrrole is synthesized by the reaction of acetylene and ammonia over a cold tube.
False
Pyrrole is a colorless non-volatile liquid that darkens readily upon exposure to air.
False
The Paal-Knorr synthesis involves a dehydration step.
True
Pyrrole is synthesized by the reaction of furan, ammonia, and oxygen over alumina catalyst.
False
The formation of the aromatic system is not a driving force of the Paal-Knorr synthesis.
False
Pyrroles react with alkyl halides and highly reactive allyl- and benzyl halides to give monoalkylated products under mild conditions.
False
The Vilsmeier reaction produces N-Acylpyrroles.
False
N-Acylpyrroles can be obtained by the reaction of alkali metal salt of pyrroles with an acyl halide.
True
Friedel-Crafts alkylation of pyrrole with a Grignard reagent produces a single product.
False
The Vilsmeier reaction requires POCI3 and N, N-dimethylformamide as reagents.
True
Friedel-Crafts alkylation of pyrrole is a simple and straightforward reaction.
False
Pyrrole undergoes diazo coupling reactions with benzenediazonium salts providing 2-aza-pyrroles.
False
Friedel-Crafts alkylation of pyrrole with a Grignard reagent produces 1-alkylpyrrole directly.
False
The rate of the diazo coupling reaction is faster in acidic media.
False
Pyrrole reacts with acetic anhydride at 100°C to produce a complex mixture.
True
The Friedel-Crafts alkylation of pyrrole with a Grignard reagent occurs at room temperature.
False
The reaction between pyrrole and benzenediazonium salts produces 2-aza-pyrroles and 2,5-bis(aza)-pyrroles simultaneously.
False
The Hofmann-Martius rearrangement is involved in the diazo coupling reaction of pyrrole with benzenediazonium salts.
False
Pyrrole reacts with CHCl3 and strong alkali to produce a complex mixture.
False
Study Notes
Synthesis of Pyrrole
- Pyrrole can be synthesized through the cyclization of 1,4-diketones with ammonia (NH3) or amines, followed by dehydration (condensation), yielding a two-double-bonded aromatic system.
- Formation of the energetically favored aromatic system is one of the driving forces of the reaction.
Methods of Synthesis
- Paal-Knorr Synthesis: cyclization of 1,4-diketones with ammonia (NH3) or amines.
- Distillation of succinimide over zinc dust.
- Heating a mixture of furan, ammonia, and steam over an alumina catalyst.
- Passing a mixture of acetylene and ammonia over a red-hot tube.
Halogenation of Pyrrole
- Pyrrole undergoes halogenation at all strongly activating positions due to its high reactivity.
- Mild conditions and special reagents are required for halogenation.
- Monohalogenated products can be obtained using bromine in carbon tetrachloride.
Acylation of Pyrrole
- Pyrrole substituted with electron-withdrawing substituents undergoes acylation at the 2-position.
- Reaction with acetic anhydride in the presence of sodium acetate provides N-acylpyrrole.
- N-Acylpyrroles can be obtained by reacting alkali metal salts of pyrroles with acyl halides.
Vilsmeier Reaction
- The Vilsmeier reaction (using POCI3 and N,N-dimethylformamide) gives 2-formylpyrrole.
Friedel-Crafts Alkylation
- Friedel-Crafts alkylation of pyrrole with alkyl halides and allyl/benzyl halides results in polyalkylation under mild conditions.
- It is not possible to obtain monoalkylated products due to the high reactivity of the pyrrole ring.
Diazo Coupling
- Pyrrole undergoes diazo coupling reactions with benzenediazonium salts, providing 2-aza- or 2,5-bis(aza)-pyrroles depending on the reaction conditions.
- The rate of the reaction is faster in alkaline media, involving pyrrolyl anion and resulting in the formation of 2,5-bis(aza)-pyrrole.
Reactions of Pyrrole
- Pyrrole undergoes diazo coupling reactions with benzenediazonium salts, resulting in 2-aza- or 2,5-bis(aza)-pyrroles depending on the reaction conditions.
- The rate of diazo coupling is faster in an alkaline media, involving the pyrrolyl anion and forming 2,5-bis(aza)-pyrrole.
Ring Opening Reaction
- Pyrrole undergoes ring opening reaction, resulting in the formation of a linear molecule.
- The reaction involves the cleavage of the pyrrole ring.
Oxidation Reaction
- Pyrrole undergoes oxidation reaction, resulting in the formation of a more oxidized product.
- The reaction involves the use of a strong oxidizing agent such as CrO3.
Reduction Reaction
- Pyrrole undergoes reduction reaction, resulting in the formation of a more reduced product.
- The reaction involves the use of a reducing agent such as Zn.
Electrophilic Substitution
- Pyrrole can react by electrophilic substitution, similar to aromatic compounds.
- The reaction involves the substitution of a hydrogen atom with an electrophile.
- Pyrrole is more reactive than benzene, making the substitution reaction easier and requiring milder reagents.
- The increased reactivity is due to the resonance of the nitrogen atom, which pushes electrons into the ring, making the carbon atoms more electron-rich.
Sulfonation
- Pyrrole can undergo sulfonation reaction, resulting in the formation of pyrrole-2-sulfonic acid.
- The reaction involves the use of a mild sulfonating agent such as pyridine-sulfur trioxide.
- The reaction conditions are mild, with a temperature of 100°C.
Friedel-Crafts Acylation
- Pyrrole can undergo Friedel-Crafts acylation reaction, resulting in the formation of 2-acetylpyrrole or 3-acetylpyrrole.
- The reaction involves the use of acetic anhydride as the acylating agent.
- The reaction conditions are severe, with a temperature of 200°C.
Friedel-Crafts Alkylation
- Pyrrole can undergo Friedel-Crafts alkylation reaction, resulting in the formation of 2-alkylpyrrole.
- The reaction involves the use of a Grignard reagent and the formation of a 1-alkylpyrrole intermediate.
- The reaction involves a Hofmann-Martius rearrangement.
Resemblance with Phenol
- Pyrrole resembles phenol in its reactivity.
- Pyrrole undergoes a Riemer-Tiemann reaction, resulting in the formation of a 2-substituted pyrrole.
- The reaction involves the use of a strong alkali and a chloroform molecule.
Sensitivity to Strong Acids
- Pyrrole is sensitive to strong acids, resulting in protonation and the formation of a pyrrole trimer.
- The reaction is considered as an electrophilic addition to pyrrole.
Pyrrole and its Properties
- Pyrrole is a colorless, volatile liquid that darkens readily upon exposure to air
- It is a weak base due to the contribution of the lone pair of electrons on the nitrogen atom to the (4n+2) electron cloud
- Pyrrole exhibits weak acidic properties due to the participation of the N lone pair in aromaticity
Synthesis of Pyrrole
- Paal-Knorr Synthesis: Pyrrole can be synthesized through the cyclization of 1,4-diketones in combination with ammonia (NH3) or amines
- The ring-closure proceeds by dehydration (condensation), which yields the two double bonds and the aromatic system
- Other methods of synthesis include:
- Distillation of succinimide over zinc dust
- Heating a mixture of furan, ammonia, and steam over an alumina catalyst
- Passing a mixture of acetylene and ammonia over a red hot tube
- Knorr-pyrrole synthesis: Condensation of α-amino ketones with a β-diketone or β-ketoester
- Hantzsch synthesis for pyrrole: Condensation between halo ketone, β-keto ester, and primary amine
Reactions of Pyrrole
- Pyrrole undergoes diazo coupling reactions readily with benzenediazonium salts, providing 2-aza- or 2,5-bis(aza)-pyrroles
- The rate of the reaction is faster in an alkaline media, involving the pyrrolyl anion and resulting in the formation of 2,5-bis(aza)-pyrrole
- N-Acylpyrroles can be obtained by the reaction of alkali metal salts of pyrroles with an acyl halide
- Vilsmeier reaction: The reaction of pyrrole with POCI3 and N,N-dimethylformamide gives 2-formylpyrrole
- Friedel-Crafts Alkylation: Pyrrole undergoes Friedel-Crafts alkylation with alkyl halides and highly reactive allyl- and benzyl halides, resulting in polyalkylation under milder conditions
- Friedel-Crafts alkylation of pyrrole with Grignard reagent produces 2-alkylpyrrole via 1-alkylpyrrole involving Hofmann-Martius rearrangement
Learn about the synthesis of pyrrole from 1,4-dicarbonyl compounds through the Paal-Knorr synthesis, involving cyclization of 1,4-diketones with ammonia or amines.
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