Org. Chem 3: Pyrrole Synthesis (Paal-Knorr Synthesis)
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Questions and Answers

What type of reagents are required for the halogenation of pyrroles?

  • Special reagents with extreme conditions
  • No reagents are required
  • Harsh reagents
  • Mild reagents (correct)

    • What is the product of the reaction of pyrrole with bromine in carbon tetrachloride?

  • 2-Bromopyrrole
  • 4-Bromopyrrole
  • 5-Bromopyrrole
  • 3-Bromopyrrole (correct)

    • What is the position of the substituent in pyrrole that undergoes iodination?

  • Position-2 (correct)
  • Position-3
  • Position-4
  • Position-5

    • What is the role of N-halosuccinimides in the preparation of 2-bromo and 2-chloropyrrole?

    <p>They are used to directly prepare the compounds</p> Signup and view all the answers

    What is the reason for the high reactivity of pyrrole ring system?

    <p>Due to the presence of a heteroatom</p> Signup and view all the answers

    What is the result of the reaction of pyrrole with bromine in carbon tetrachloride?

    <p>Monobromination of pyrrole</p> Signup and view all the answers

    What is the reactant that provides N-acylpyrrole in the given reaction?

    <p>Pyrrole</p> Signup and view all the answers

    What is the condition required for the bromination of pyrrole?

    <p>Low temperature and pressure</p> Signup and view all the answers

    What is the temperature at which the reaction between pyrrole and acetic anhydride takes place?

    <p>200°C</p> Signup and view all the answers

    What is the effect of electron-withdrawing substituent on the pyrrole ring system?

    <p>It increases the reactivity of the ring system</p> Signup and view all the answers

    What is the role of sodium acetate in the reaction?

    <p>Presence</p> Signup and view all the answers

    What is the percentage of 2-acytal pyrrole formed in the reaction?

    <p>90%</p> Signup and view all the answers

    What is the byproduct of the reaction?

    <p>CH3COOH</p> Signup and view all the answers

    What is the other product formed in the reaction besides N-acylpyrrole?

    <p>Acetic acid</p> Signup and view all the answers

    What is the general method of synthesizing substituted pyrroles?

    <p>Cyclization of 1,4-diketones in combination with ammonia or amines</p> Signup and view all the answers

    What is the driving force of the reaction in the Paal-Knorr synthesis?

    <p>The formation of a stable aromatic system</p> Signup and view all the answers

    What is the product of the reaction between acetylene and ammonia over red hot tube?

    <p>Pyrrole</p> Signup and view all the answers

    What is the role of zinc dust in the synthesis of pyrrole?

    <p>It is used for distillation</p> Signup and view all the answers

    What is the byproduct of the reaction between 1,4-diketones and ammonia or amines?

    <p>Water</p> Signup and view all the answers

    What is the purpose of reflux in the Paal-Knorr synthesis?

    <p>To heat the reaction mixture</p> Signup and view all the answers

    What is the product of the reaction between furan, ammonia, and steam over alumina catalyst?

    <p>Pyrrole</p> Signup and view all the answers

    What is the advantage of the Paal-Knorr synthesis?

    <p>It produces a stable aromatic system</p> Signup and view all the answers

    What is the result of the reaction of alkali metal salt of pyrroles with an acyl halide?

    <p>N-Acylpyrroles</p> Signup and view all the answers

    What is the name of the reaction that produces 2-Formylpyrrole?

    <p>Vilsmeier reaction</p> Signup and view all the answers

    What is the problem with Friedel-Crafts alkylation of pyrrole?

    <p>It is not possible to obtain monoalkylated product</p> Signup and view all the answers

    What is used as a reagent in the Vilsmeier reaction?

    <p>POCI3 and N, N-dimethylformamide</p> Signup and view all the answers

    What type of halides can be used in Friedel-Crafts alkylation of pyrrole?

    <p>Alkyl, allyl- and benzyl halides</p> Signup and view all the answers

    What is the product of the reaction between alkali metal salt of pyrroles and an acyl halide?

    <p>N-Acylpyrroles</p> Signup and view all the answers

    What is the product of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>2-alkylpyrrole</p> Signup and view all the answers

    What is the condition required for the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>Alkaline media</p> Signup and view all the answers

    What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>Pyrrolyl anion</p> Signup and view all the answers

    What is the product of the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>2,5-bis(aza)-pyrrole</p> Signup and view all the answers

    What is the reagent used in the Friedel-Crafts alkylation of pyrrole?

    <p>Grignard reagent</p> Signup and view all the answers

    At what temperature does the Friedel-Crafts alkylation of pyrrole with a Grignard reagent take place?

    <p>100°C</p> Signup and view all the answers

    What is the byproduct of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>Complex mixture</p> Signup and view all the answers

    What is the type of rearrangement involved in the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>Hofmann-Martius rearrangement</p> Signup and view all the answers

    What is the reaction that occurs when pyrrole reacts with CHCl3 and strong alkali?

    <p>Riemer Tiemann reaction</p> Signup and view all the answers

    What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>Carbine</p> Signup and view all the answers

    What is the product of the reaction between alkali metal salt of pyrroles and an acyl halide?

    <p>N-Acylpyrrole</p> Signup and view all the answers

    What is the purpose of reflux in the Paal-Knorr synthesis?

    <p>To drive the reaction forward</p> Signup and view all the answers

    What is the yield of the corresponding pyrrole-2-sulfonic acid obtained when pyrrole reacts with pyridine-sulfur trioxide complex at 100°C?

    <p>90%</p> Signup and view all the answers

    What is the role of zinc dust in the synthesis of pyrrole?

    <p>To reduce the reaction mixture</p> Signup and view all the answers

    What is the main product formed when pyrrole reacts with acetic anhydride at 200°C?

    <p>2-Acetylpyrrole</p> Signup and view all the answers

    What is the product of the reaction between furan, ammonia, and steam over alumina catalyst?

    <p>Pyridine</p> Signup and view all the answers

    What is required for the sulfonation of pyrroles substituted with electron-withdrawing substituents?

    <p>Vigorous reaction conditions</p> Signup and view all the answers

    What is the result of the reaction of pyrrole with bromine in carbon tetrachloride?

    <p>2-Bromopyrrole</p> Signup and view all the answers

    What is the driving force of the reaction in the Paal-Knorr synthesis?

    <p>Heat</p> Signup and view all the answers

    How can N-Acetylpyrrole be obtained in high yield?

    <p>By heating pyrrole with N-acetylimidazole</p> Signup and view all the answers

    What is the role of pyridine in the sulfonation of pyrrole?

    <p>It forms a complex with sulfur trioxide</p> Signup and view all the answers

    What is the byproduct formed in the direct acetylation of pyrrole with acetic anhydride?

    <p>3-Acetylpyrrole</p> Signup and view all the answers

    Why is pyrrole more reactive than benzene?

    <p>Because of the resonance that pushes the electrons from the N-atom into the ring</p> Signup and view all the answers

    What happens when pyrrole reacts with strong acids?

    <p>It forms a pyrrole trimer</p> Signup and view all the answers

    What is the difference between the reactivity of pyrrole and benzene?

    <p>Pyrrole is more reactive than benzene</p> Signup and view all the answers

    What type of reaction is involved in the acylation of pyrrole?

    <p>Acylation</p> Signup and view all the answers

    Why are modified reagents used in the electrophilic substitution of pyrrole?

    <p>To avoid the use of strong acids that induce polymerization</p> Signup and view all the answers

    What is the result of the reaction of pyrrole with isocyanate?

    <p>Formation of a phenyl isocyanate</p> Signup and view all the answers

    Why is pyrrole sensitive to strong acids?

    <p>Due to the protonation that occurs at one of C-3</p> Signup and view all the answers

    What is the characteristic of pyrrole that resembles the most reactive benzene derivatives?

    <p>Electron-rich c-atoms in the ring</p> Signup and view all the answers

    What is the product of the reaction between pyrrole and acetic anhydride in the presence of sodium acetate?

    <p>N-acylpyrrole</p> Signup and view all the answers

    What is the ratio of 2-acytal pyrrole to 3-acytal pyrrole in the given reaction?

    <p>90:10</p> Signup and view all the answers

    What is the reagent that provides N-acylpyrrole in the given reaction?

    <p>Acetic anhydride</p> Signup and view all the answers

    At what temperature does the reaction between pyrrole and acetic anhydride take place?

    <p>200°C</p> Signup and view all the answers

    What is the role of sodium acetate in the reaction?

    <p>Base</p> Signup and view all the answers

    What is the byproduct of the reaction between pyrrole and acetic anhydride?

    <p>CH3COOH</p> Signup and view all the answers

    What is the major product of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>2-Alkylpyrrole</p> Signup and view all the answers

    What is the condition required for the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>Alkaline media</p> Signup and view all the answers

    What is the intermediate involved in the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>Pyrrolyl anion</p> Signup and view all the answers

    What is the product of the diazo coupling reaction of pyrrole with benzenediazonium salts?

    <p>2,5-Bis(aza)-pyrrole</p> Signup and view all the answers

    What type of rearrangement is involved in the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>Hofmann-Martius rearrangement</p> Signup and view all the answers

    What is the temperature at which the Friedel-Crafts alkylation of pyrrole with a Grignard reagent takes place?

    <p>100°C</p> Signup and view all the answers

    What is the byproduct of the Friedel-Crafts alkylation of pyrrole with a Grignard reagent?

    <p>Complex mixture</p> Signup and view all the answers

    What is the purpose of using a Grignard reagent in the Friedel-Crafts alkylation of pyrrole?

    <p>To introduce an alkyl group at the 2-position</p> Signup and view all the answers

    Pyrrole reacts with CHCl3 and strong alkali to form two types of products.

    <p>True</p> Signup and view all the answers

    Diazo coupling occurs at the A position if both the X-positions are occupied.

    <p>False</p> Signup and view all the answers

    Ring opening reaction occurs in the presence of NH,OH / EtOH under reflux conditions.

    <p>True</p> Signup and view all the answers

    Oxidation reaction occurs in the presence of CrO3 / CH3COOH.

    <p>True</p> Signup and view all the answers

    Reduction reaction occurs in the presence of Zn / CH3COOH.

    <p>True</p> Signup and view all the answers

    The Riemer-Tiemann reaction is a type of formylation reaction.

    <p>True</p> Signup and view all the answers

    Pyrrole resembles phenol in its chemical properties.

    <p>True</p> Signup and view all the answers

    Carbine insertion reaction occurs in the reaction of pyrrole with CHCl3 and strong alkali.

    <p>True</p> Signup and view all the answers

    Pyrrole is a strong base because the lone pair of electron of the nitrogen atom contributes to the aromaticity.

    <p>False</p> Signup and view all the answers

    The Knorr-pyrrole synthesis involves the condensation of a-amino ketones with a f-diketone or a B-ketoester to give a substituted pyrrole.

    <p>True</p> Signup and view all the answers

    Pyrrole is synthesized by the reaction of furan, ammonia, and steam over palladium catalyst.

    <p>False</p> Signup and view all the answers

    The Paal-Knorr synthesis involves the cyclization of 1,4-diketones in combination with ammonia (NH3) or amines.

    <p>True</p> Signup and view all the answers

    Pyrrole exhibits strong acidic properties due to participation of N lone pair in aromaticity.

    <p>False</p> Signup and view all the answers

    Pyrrole can be obtained by distillation of succinimide over copper dust.

    <p>False</p> Signup and view all the answers

    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.

    <p>True</p> Signup and view all the answers

    The Paal-Knorr synthesis yields a non-aromatic system.

    <p>False</p> Signup and view all the answers

    Hantzsch synthesis for pyrrole involves the condensation of halo ketone, B-keto ester and primary amine.

    <p>True</p> Signup and view all the answers

    Pyrrole is synthesized by the reaction of acetylene and ammonia over a cold tube.

    <p>False</p> Signup and view all the answers

    Pyrrole is a colorless non-volatile liquid that darkens readily upon exposure to air.

    <p>False</p> Signup and view all the answers

    The Paal-Knorr synthesis involves a dehydration step.

    <p>True</p> Signup and view all the answers

    Pyrrole is synthesized by the reaction of furan, ammonia, and oxygen over alumina catalyst.

    <p>False</p> Signup and view all the answers

    The formation of the aromatic system is not a driving force of the Paal-Knorr synthesis.

    <p>False</p> Signup and view all the answers

    Pyrroles react with alkyl halides and highly reactive allyl- and benzyl halides to give monoalkylated products under mild conditions.

    <p>False</p> Signup and view all the answers

    The Vilsmeier reaction produces N-Acylpyrroles.

    <p>False</p> Signup and view all the answers

    N-Acylpyrroles can be obtained by the reaction of alkali metal salt of pyrroles with an acyl halide.

    <p>True</p> Signup and view all the answers

    Friedel-Crafts alkylation of pyrrole with a Grignard reagent produces a single product.

    <p>False</p> Signup and view all the answers

    The Vilsmeier reaction requires POCI3 and N, N-dimethylformamide as reagents.

    <p>True</p> Signup and view all the answers

    Friedel-Crafts alkylation of pyrrole is a simple and straightforward reaction.

    <p>False</p> Signup and view all the answers

    Pyrrole undergoes diazo coupling reactions with benzenediazonium salts providing 2-aza-pyrroles.

    <p>False</p> Signup and view all the answers

    Friedel-Crafts alkylation of pyrrole with a Grignard reagent produces 1-alkylpyrrole directly.

    <p>False</p> Signup and view all the answers

    The rate of the diazo coupling reaction is faster in acidic media.

    <p>False</p> Signup and view all the answers

    Pyrrole reacts with acetic anhydride at 100°C to produce a complex mixture.

    <p>True</p> Signup and view all the answers

    The Friedel-Crafts alkylation of pyrrole with a Grignard reagent occurs at room temperature.

    <p>False</p> Signup and view all the answers

    The reaction between pyrrole and benzenediazonium salts produces 2-aza-pyrroles and 2,5-bis(aza)-pyrroles simultaneously.

    <p>False</p> Signup and view all the answers

    The Hofmann-Martius rearrangement is involved in the diazo coupling reaction of pyrrole with benzenediazonium salts.

    <p>False</p> Signup and view all the answers

    Pyrrole reacts with CHCl3 and strong alkali to produce a complex mixture.

    <p>False</p> Signup and view all the answers

    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

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    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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