Arenediazonium Salts With Diazo Coupling and Sandmeyer Reactions
TLDRThis chemistry tutorial delves into the synthesis of aryl diazonium salts, starting from benzene through nitration and reduction to form aniline, followed by reaction with sodium nitrite to create the diazonium salt. It explores various Sandmeyer reactions for halide substitution and other transformations, including the synthesis of 1,3,5-tribromobenzene. The script also covers diazo coupling reactions, illustrating the formation of azo compounds from phenol and diazonium salts, highlighting the importance of strong activating groups and the resulting cis-trans isomerism.
Takeaways
- 🔬 The script discusses the synthesis of aryl diazonium salts starting from benzene, involving aromatic nitration, reduction to aniline, and then reaction with sodium nitrite and hydrochloric acid.
- ⚗️ Aryl diazonium salts can be used in various reactions such as Sandmeyer reactions, where the diazonium salt reacts with copper halide salts to substitute the diazonium group with halogens.
- 🌐 The Sandmeyer reaction can produce different halogenated benzene derivatives, including bromobenzene, benzene with a CN group, and iodobenzene, depending on the copper halide salt used.
- 🔄 The script also covers the conversion of aryl diazonium salts to other compounds like phenol and benzene itself using specific reagents like hypophosphorus acid (H3PO2).
- 🧪 A synthesis problem is presented to demonstrate the conversion of nitrobenzene to benzene, involving steps of reduction and use of hypophosphorus acid.
- 📚 The synthesis of 1,3,5-tribromobenzene is explained, highlighting the importance of the ortho-para directing effect of the NH2 group and the use of diazonium salts in meta-selective bromination.
- 🔗 Diazo coupling reactions are introduced, where aryl diazonium salts react with phenol to form azo compounds, with the mechanism involving nucleophilic attack and aromatic ring restoration.
- 📉 The stability of azo compounds is affected by the geometric isomerism (cis and trans), with the trans isomer being more stable due to less steric strain.
- 🛠 The role of a strong activating group, such as OH, is emphasized in the diazo coupling reaction, as it makes the ring more nucleophilic and reactive towards the weak electrophile, the diazonium salt.
- 🔍 An alternative mechanistic explanation is provided for the diazo coupling reaction, illustrating the effect of the activating group on the ring and the transfer of ions during the reaction.
- 📝 The script serves as an educational resource for understanding the versatility of aryl diazonium salts in organic synthesis and the principles behind their reactions.
Q & A
What is the first step in synthesizing an aryl diazonium salt?
-The first step in synthesizing an aryl diazonium salt is aromatic nitration, where an NO2 group is installed onto the benzene ring to form nitrobenzene.
What reagents are used to reduce nitrobenzene to an NH2 group?
-A metal such as iron, along with hydrochloric acid, is used to reduce nitrobenzene to an NH2 group, resulting in aniline.
How is the final step of synthesizing an aryl diazonium salt carried out?
-The final step involves reacting the NH2 group with sodium nitrite and hydrochloric acid at low temperatures to form the aryl diazonium salt.
What is the Sandmeyer reaction and what does it achieve?
-The Sandmeyer reaction is a process where an aryl diazonium salt reacts with a copper(I) halide, leading to the replacement of the N2 group with a halogen atom, such as chlorine, bromine, or iodine, to form halogenated benzene derivatives.
What is the leaving group in the Sandmeyer reaction?
-The leaving group in the Sandmeyer reaction is nitrogen gas (N2), which is a very stable molecule and its formation drives the reaction forward.
How can one synthesize bromobenzene using the Sandmeyer reaction?
-Bromobenzene can be synthesized by reacting an aryl diazonium salt with copper bromide, which replaces the N2 group with a bromine atom.
What is the purpose of using H3PO2 in the synthesis of benzene from an aryl diazonium salt?
-H3PO2, or hypophosphorus acid, is used to replace the N2 group in the aryl diazonium salt with a hydrogen atom, effectively converting the compound back to benzene.
How can phenol be synthesized from an aryl diazonium salt?
-Phenol can be synthesized by reacting an aryl diazonium salt with copper(II) nitrate and water, or by using copper oxide with the aryl diazonium salt.
What is the key challenge in synthesizing 1,3,5-tribromobenzene from benzene?
-The key challenge is to ensure that the bromine atoms are placed in meta positions relative to each other, which requires a strategic sequence of nitration, reduction, and bromination steps.
What is the azo coupling reaction and what type of linkage does it form?
-The azo coupling reaction is a process where an aryl diazonium salt reacts with a nucleophilic compound, such as phenol, to form an azo linkage, which is a double bond between the two nitrogen atoms connecting the two aromatic rings.
What factors affect the stability of the azo compound formed in the azo coupling reaction?
-The stability of the azo compound is affected by the presence of strongly activating groups, such as OH or NH2, and the steric strain between the two aromatic rings, with the trans isomer being more stable due to less steric strain.
Outlines
🧪 Synthesis of Aryl Diazonium Salts and Sandby Reactions
This paragraph introduces the synthesis of aryl diazonium salts starting from benzene through a series of reactions including aromatic nitration, reduction to form aniline, and finally diazotization with sodium nitrite and hydrochloric acid to yield the diazonium salt. It also covers the Sandby reaction, where the diazonium salt reacts with copper(I) halides to substitute the diazonium group with halogens, resulting in products like bromobenzene and iodobenzene. The paragraph discusses other substitutions like with copper cyanide and the use of HBF4 for fluorination. It also mentions the conversion of diazonium salts to phenol using H3PO2 or through a reaction involving copper oxide, copper(II) nitrate, and water.
🔍 Strategies for Benzene Derivatives Synthesis
The second paragraph delves into problem-solving for the synthesis of benzene derivatives, specifically focusing on the conversion of nitrobenzene to benzene by reduction using metals and hydrochloric acid to form aniline, followed by diazotization. It then presents a synthesis challenge for creating 1,3,5-tribromobenzene, discussing the ineffectiveness of direct bromination due to the directing effects of the substituents and the need for an alternative method involving nitration, reduction to aniline, bromination with directing effects, and finally the use of hypophosphorous acid to replace the diazonium group with hydrogen, yielding the desired product.
🔗 Azo Coupling Reactions and Mechanistic Insights
This section discusses azo coupling reactions, starting with the reaction of phenol with an aryl diazonium salt to form an azo linkage. It explains the nucleophilic attack of the phenol ring on the diazonium salt, the formation of a double bond, and the subsequent base-assisted removal of a proton to reform the aromatic ring, resulting in an azo compound. The paragraph also addresses the importance of a strong activating group on the nucleophile for the reaction to proceed and presents two possible isomers: the more stable trans and the less stable cis form. Additionally, it provides an alternative mechanistic view that illustrates the influence of the activating group on the ring, making it more nucleophilic and reactive towards the diazonium salt.
📚 Advanced Mechanism of Azo Compound Formation
The final paragraph provides a deeper look into the mechanism of azo compound formation, emphasizing the role of the phenol's hydroxyl group in enhancing the ring's nucleophilicity. It describes the initial weak electrophile status of the diazonium salt, the displacement of a proton by an electrophile, and the formation of an intermediate with a positive charge on oxygen. The summary details the movement of double bonds and the conversion of the triple bond to a double bond, leading to the formation of the azo linkage. It concludes with the removal of a proton by a base and the restoration of the aromatic ring, resulting in the azo compound, which can exist in both cis and trans isomers, and highlights the steric factors affecting their stability.
Mindmap
Keywords
💡Diazonium Salts
💡Aromatic Nitration
💡Reduction
💡Sandmeyer Reaction
💡Coupling Reaction
💡Activating Group
💡Deactivating Group
💡Ortho and Para Positions
💡Hypo Phosphorus Acid (H3PO2)
💡Azo Compound
💡Steric Strain
Highlights
Introduction to the synthesis of aryl diazonium salts starting with benzene.
Aromatic nitration to install a NO2 group on the benzene ring to form nitrobenzene.
Reduction of nitrobenzene using iron and hydrochloric acid to form an NH2 group.
Final step in synthesizing aryl diazonium salt involves reaction with sodium nitrite and hydrochloric acid.
Aryl diazonium salts can be used in various reactions, such as Sandmeyer reactions and diazo coupling.
Sandmeyer reaction involves replacing the N2 group with halogens like chlorine, bromine, or iodine.
Copper cyanide can be used to introduce a CN group in place of the N2 group.
HBF4 can replace the N2 group with a fluorine atom to synthesize fluorobenzene.
Conversion of aryl diazonium salt to phenol using hypophosphorus acid (H3PO2).
Copper oxide and copper II nitrate can also be used to synthesize phenol from aryl diazonium salt.
Method to convert nitrobenzene back to benzene by removing the nitro group.
Synthesis of 1,3,5-tribromo benzene using a series of reactions starting with aniline.
Diazo coupling reaction mechanism involving phenol and aryl diazonium salt to form an azo linkage.
Formation of azo compounds with cis and trans isomers due to the orientation of benzene rings.
Detailed mechanism showing the effect of the OH group on the ring and its role in the diazo coupling reaction.
Importance of a strong activating group for the nucleophile in diazo coupling reactions.
Steric factors influencing the stability of the trans isomer over the cis isomer in azo compounds.
Transcripts
Browse More Related Video
Diazonium Salts & Nucleophilic Aromatic Substitution: Crash Course Organic Chemistry #47
Benzene Side Chain Reactions
22.5 Sandmeyer Reactions | Organic Chemistry
Electrophilic Aromatic Substitution Reactions Made Easy!
Amines: Crash Course Organic Chemistry #46
More EAS & Benzylic Reactions: Crash Course Organic Chemistry #39
5.0 / 5 (0 votes)
Thanks for rating: