Bromination of Aniline | Electrophilic Aromatic Substitution Reactions | Chemistry | Khan Academy
Description In this video, we will look at the product that is formed when aniline undergoes bromination. We will also see how to modify the substrate, aniline, in order to selectively obtain the para-product. Practice this concept - https://www.khanacademy.org/science/organic-chemistry-essentials/x1918b84b5bb1f2e6:electrophilic-aromatic-substitution-reactions/x1918b84b5bb1f2e6:the-curious-case-of-phenol-and-aniline/e/interesting-behaviour-of-aniline-towards-eas Master the concept of “Bromination of Aniline” through practice exercises and videos - https://www.khanacademy.org/science/organic-chemistry-essentials/x1918b84b5bb1f2e6:electrophilic-aromatic-substitution-reactions/x1918b84b5bb1f2e6:the-curious-case-of-phenol-and-aniline/v/nitration-of-phenols Check out more videos and exercises on “Electrophilic Aromatic Substitution Reactions” - https://www.khanacademy.org/science/organic-chemistry-essentials/x1918b84b5bb1f2e6:electrophilic-aromatic-substitution-reactions To get you fully ready for your exam and help you fall in love with “Organic Chemistry”, find the complete bank of exercises and videos for “Organic Chemistry Essentials” here - https://www.khanacademy.org/science/organic-chemistry-essentials Khan Academy is a free learning platform for Class 1-12 students with videos, exercises, and tests for maths, science, and more subjects. Our content is aligned to CBSE syllabus and available in Hindi, English, and many more regional languages. Experience the joy of easy, seamless, accessible learning anywhere, anytime with Khan Academy. Subscribe to our YouTube channel - https://www.youtube.com/c/khanacademy As a 501(c)(3) nonprofit organization, we would love your help! Donate here: https://www.khanacademy.org/donate?utm_source=youtube&utm_medium=desc Created by Jitin Nair
Bromination of Aniline | Electrophilic Aromatic Substitution Reactions | Chemistry | Khan Academy
Introduction to Bromination of Aniline
In this section, we learn about the bromination of aniline and its reaction mechanism. We explore the role of aniline's lone pair and the use of bromine water as a polar solvent.
Bromination Reaction Mechanism
- Bromination reactions are a type of electrophilic substitution reactions commonly performed in the lab.
- Aniline has a lone pair that it shares with the ring through resonance, making it ortho-para directing.
- Bromine water is used as a polar solvent to break the bromine-bromine bond, resulting in a positive and negative charge on bromine.
- The electrophile, bromine with a positive charge, adds to both ortho positions and para position, leading to 2,4,6-tribromoaniline.
Attempting Mono-Bromination
Here we explore how changing the solvent and reaction conditions can affect the outcome of mono-bromination.
Using Non-Polar Solvent (CS2)
- Carbon disulfide (CS2), a non-polar solvent, is used instead of water.
- CS2 does not easily break bromine bonds, resulting in fewer electrophiles available for reaction.
- Performing the reaction at low temperature further reduces the number of available electrophiles.
- Despite these changes, multiple substitutions still occur on the same ring due to nitrogen's highly activating effect.
Engaging Lone Pair for Selective Mono-Bromination
This section explores how blocking nitrogen's reactivity can lead to selective mono-bromination by engaging its lone pair differently.
Reacting with Acetic Anhydride
- Acetic anhydride is used to react with aniline's lone pair, blocking its reactivity.
- The carbon-oxygen bond in acetic anhydride breaks, and the resulting group attaches to nitrogen.
- This engagement of the lone pair reduces its contribution to resonance, making the ring less reactive.
- Bromination after this step results in bromine adding only at the para position due to steric hindrance from the bulky group.
Conclusion
The bromination of aniline involves electrophilic substitution reactions. By understanding the role of aniline's lone pair and modifying reaction conditions, it is possible to achieve selective mono-bromination. Blocking nitrogen's reactivity through a reaction with acetic anhydride can lead to desired outcomes.
Bromination and Ortho-Para Directing Groups
This section discusses the bromination reaction and the role of ortho-para directing groups in determining the major and minor products.
Bromination Reaction
- Bromination of a compound with an NH2 group results in a higher activation of the ring compared to other groups.
- The presence of a bulky group can hinder bromine attachment to the ortho positions, leading to the para product as the major product.
- Steric hindrance from the bulky group reduces the formation of the minor ortho product.
Blocking Nitrogen Lone Pair for Reactivity Control
This section explains how blocking nitrogen lone pair can control reactivity in reactions.
Reactive Ring and Lone Pair
- The lone pair on nitrogen makes the ring highly reactive.
- Blocking nitrogen with a group that allows resonance with oxygen helps control reactivity.
Electrophilic Aromatic Substitution: Friedel-Crafts Reactions
This section introduces electrophilic aromatic substitution reactions, specifically focusing on Friedel-Crafts alkylation.
Friedel-Crafts Alkylation
- Friedel-Crafts alkylation involves substituting an alkyl group onto an aromatic ring using a Lewis acid catalyst (e.g., AlCl3).
- Aniline undergoes Friedel-Crafts alkylation similarly, but there is an issue due to its lone pair on nitrogen.
Unexpected Results from Nitrogen Lone Pair in Friedel-Crafts Reactions
This section explores how the lone pair on nitrogen causes unexpected results in Friedel-Crafts reactions.
Nitrogen's Role in Friedel-Crafts Alkylation
- In Friedel-Crafts alkylation of aniline, the lone pair on nitrogen acts as a Lewis base.
- The reaction starts with the formation of a complex between AlCl3 and the lone pair on nitrogen.
- This complex prevents further reaction by pulling electrons from the ring.
Similar Issues in Friedel-Crafts Acylation
This section highlights similar issues caused by the nitrogen lone pair in Friedel-Crafts acylation reactions.
Nitrogen's Role in Friedel-Crafts Acylation
- In Friedel-Crafts acylation, a similar situation occurs where the lone pair on nitrogen forms a complex with AlCl3.
- This complex hinders further reaction, similar to what happens in Friedel-Crafts alkylation.
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