Diazomethane Synthesis and Applications (Arndt-Eistert Homologation)
TLDRThis tutorial delves into the synthesis and applications of diazomethane, a highly reactive compound used in organic chemistry. It is synthesized from N-methyl-N-nitrosotoluenesulfonamide using sodium hydroxide in ether, resulting in a zwitterionic form that is unstable and should be used immediately. Diazomethane's applications include converting carboxylic acids into methyl esters and phenols into methyl ethers, as well as the Arndt-Eistert homologation for extending carboxylic acid chains by one carbon atom. The process involves nucleophilic attack, Wolff rearrangement, and ketene formation, offering a valuable synthetic technique for creating carboxylic acids of varying chain lengths.
Takeaways
- 🧪 Diazomethane is commonly synthesized from N-methyl-N-nitrosotoluenesulfonamide using sodium hydroxide in ether.
- 🔍 The synthesis involves a mechanism where hydroxide ions attack the sulfur atom and protonate the intermediates, leading to the formation of diazomethane.
- ⚠️ Diazomethane is highly explosive and should only be handled by trained chemists.
- 🔑 Diazomethane is used to convert carboxylic acids into methyl esters via a simple protonation and substitution reaction.
- 🌟 The resonance structure of diazomethane allows for its carbanion to be protonated, facilitating the SN2 reaction with carboxylate anions.
- 🍃 Diazomethane can also methylate phenols due to their relative acidity and resonance stabilization of the conjugate base.
- 🚫 Normal alcohols are not acidic enough to protonate diazomethane under normal conditions.
- 🌞 Alcohols can be methylated by diazomethane under specific light irradiation conditions, which will be discussed in later tutorials.
- 🔄 Diazomethane is crucial for the Arndt-Eistert homologation, a method to extend the carbon chain of carboxylic acids by one atom.
- 🔬 The Arndt-Eistert process involves the conversion of carboxylic acids to acid chlorides and subsequent reaction with diazomethane to form an alpha diazoketone.
- 🔄 The Wolff rearrangement, a 1,2-shift, occurs during the homologation process, converting the intermediate into a more stable ketene.
- 🛠️ Homologation can be repeated to synthesize carboxylic acids of any desired chain length, making it a valuable synthetic technique.
Q & A
What is a common method for carbene formation mentioned in the script?
-A common method for carbene formation is through the decomposition of diazomethane.
What compound is used to synthesize diazomethane as described in the script?
-Diazomethane can be synthesized from N-methyl-N-nitrosotoluenesulfonamide.
What is the role of sodium hydroxide in the synthesis of diazomethane?
-Sodium hydroxide in ether is used to treat the starting compound, facilitating the reaction mechanism that leads to the formation of diazomethane.
Why is diazomethane co-distilled with ether after its formation?
-Diazomethane is co-distilled with ether to facilitate its use directly, as it is quite explosive and should not be stored.
What is the primary reason diazomethane is titrated with a carboxylic acid immediately after synthesis?
-Diazomethane is titrated with a carboxylic acid to stabilize it due to its explosive nature and to use it directly in reactions.
How can diazomethane be used to convert carboxylic acids into methyl esters?
-Diazomethane can be protonated by the carboxylic acid to form a diazonium cation, which then undergoes an SN2 reaction with the carboxylate anion to form a methyl ester and release molecular nitrogen.
Why is diazomethane effective for methylating phenols but not normal alcohols?
-Phenols can be methylated by diazomethane due to their relative acidity and resonance stabilization of the conjugate base, while normal alcohols lack sufficient acidity to protonate diazomethane.
What is the photochemical process that allows for the methylation of normal alcohols using diazomethane?
-The photochemical process involves irradiating the mixture of diazomethane and alcohol with light of a particular wavelength, which facilitates the methylation reaction.
What is the Arndt-Eistert homologation, and how does it involve diazomethane?
-The Arndt-Eistert homologation is a reaction that allows for the insertion of a carbon atom between the carboxyl carbon and the adjacent carbon of a carboxylic acid, effectively lengthening the carbon chain by one. Diazomethane plays a key role in this reaction after the carboxylic acid is converted into an acid chloride.
What is the intermediate formed when diazomethane reacts with an acid chloride, and what is its significance?
-The intermediate formed is an alpha diazoketone, which upon heating, loses nitrogen gas to form an acyl carbene. This intermediate is significant as it leads to the formation of a ketene through a Wolff rearrangement.
What is the final product of the Arndt-Eistert homologation reaction, and how is it obtained?
-The final product is a carboxylic acid with one more carbon than the original. It is obtained through the hydrolysis of the ketene formed after the Wolff rearrangement, where water performs a nucleophilic attack.
Why is the Arndt-Eistert homologation considered valuable in synthetic chemistry?
-The Arndt-Eistert homologation is valuable because it allows for the repeated extension of the carbon chain of a carboxylic acid to any desired length, providing a versatile synthetic technique.
Outlines
🧪 Synthesis and Applications of Diazomethane
This paragraph discusses the synthesis of diazomethane from N-methyl-N-nitrosotoluenesulfonamide using sodium hydroxide in ether, detailing the mechanism of its formation through a series of reactions involving hydroxide ions and nitrogen atoms. The paragraph also highlights the explosive nature of diazomethane and the necessity for trained chemists to handle it. Applications include converting carboxylic acids into methyl esters, methylating phenols, and the homologation of carboxylic acids by one carbon atom through the Arndt-Eistert homologation process, which involves the insertion of a carbon atom between the carboxyl carbon and the adjacent carbon, leading to a longer carbon chain. The paragraph concludes with the Wolff rearrangement, which results in the formation of a ketene and ultimately a carboxylic acid with an extended chain.
🔬 Repeatability of Diazomethane Homologation
The second paragraph emphasizes the versatility of the homologation reaction using diazomethane. It explains that once the initial homologation is completed, the process can be repeated multiple times to synthesize carboxylic acids of varying chain lengths. This feature makes diazomethane a valuable tool in synthetic chemistry, allowing for the creation of a wide range of carboxylic acid derivatives tailored to specific needs.
Mindmap
Keywords
💡Carbenes
💡Diazomethane
💡N-methyl-N-nitrosotoluenesulfonamide
💡Sodium Hydroxide
💡Ether
💡Zwitterionic Form
💡Explosive
💡Carboxylic Acids
💡Methyl Esters
💡Phenols
💡Arndt-Eistert Homologation
💡Wolff Rearrangement
Highlights
Diazomethane is commonly synthesized for carbene formation.
Synthesis involves decomposition of N-methyl-N-nitrosotoluenesulfonamide with sodium hydroxide in ether.
Mechanism involves hydroxide ion attacking sulfur, proton transfer, and nitrogen pushing lone pair to form zwitterionic diazomethane.
Diazomethane is co-distilled in ether and titrated with carboxylic acid before use due to its explosive nature.
Diazomethane converts carboxylic acids into methyl esters, avoiding typical acid catalysis.
Resonance structure of diazomethane allows carbanion protonation by carboxylic acid, forming diazonium cation.
Diazonium cation undergoes SN2 reaction with carboxylate anion, yielding methyl ester and nitrogen gas.
Phenols can also be methylated by diazomethane due to their relative acidity and resonance stabilization.
Normal alcohols are not acidic enough for methylation with diazomethane without photochemical assistance.
Diazomethane can homologate carboxylic acids by inserting a carbon atom, a reaction known as Arndt-Eistert homologation.
Homologation involves conversion of carboxylic acid to acid chloride and nucleophilic attack by diazomethane.
Triethylamine acts as a proton sponge in the formation of alpha diazoketone.
Heating alpha diazoketone leads to loss of nitrogen gas and formation of acyl carbene.
Acyl carbene undergoes Wolff rearrangement, forming a more stable ketene.
Hydrolysis of ketene results in the carboxylic acid with an extended carbon chain.
Arndt-Eistert homologation can be repeated to synthesize carboxylic acids of any desired chain length.
Diazomethane provides a valuable synthetic technique for organic chemistry.
Transcripts
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