Swern Oxidation of Alcohols | A useful alternative to PCC
TLDRThis video script delves into the Swern oxidation, a pivotal technique in organic chemistry developed in the 1970s. It outlines the two-phase mechanism, starting with the formation of a sulfonium ion using DMSO and oxal chloride, followed by an SN2 reaction with an alcohol. The script clarifies misconceptions about the reaction's mechanism, emphasizing the correct pathway involving triethylamine as a base. The tutorial also illustrates the reaction's selectivity with examples, including its impact on primary and secondary alcohols and its compatibility with other functional groups. The video aims to prepare students for exams, highlighting the importance of understanding and practicing this commonly tested reaction.
Takeaways
- 🕒 The SRN1 reaction was developed by Daniel Sr in the 1970s and has become a staple in organic chemistry courses.
- 📚 The SRN1 reaction is taught in textbooks alongside DMSO-based methods, but the SRN1 excitation is particularly highlighted.
- 🔍 The SRN1 reaction proceeds in two distinct phases, starting with the creation of a sulfonium cation that reacts with an alcohol.
- 🧪 The first step involves a nucleophilic attack by DMSO on oxal chloride, leading to a tetrahedral intermediate and the formation of a sulfur-containing group.
- 💥 A complex cascade of electron movements results in the formation of dimethyl chlorosulfonium chloride, with byproducts like carbon monoxide and carbon dioxide.
- 🔄 Alternative methods to form the sulfonium ion include reactions with dimethyl sulfide and chlorine or with NCS (N-chlorosuccinimide).
- 🌟 Oxal chloride is notorious for being a reagent that many chemists dislike due to its properties, including smell.
- 🍻 The sulfonium ion reacts with an alcohol in an SN2 fashion, displacing the chlorine and forming an intermediate.
- 🧬 The intermediate is then deprotonated by the released chloride anion, and a base like triethylamine is used to facilitate the final product formation.
- 📉 Contrary to some teachings, research indicates that the deprotonation occurs on the methyl group attached to sulfur before the intra-molecular proton transfer.
- 🌐 The SRN1 reaction is known for its chemical activity, selectively oxidizing primary alcohols to aldehydes without affecting other functional groups like double bonds or ethers.
- 💬 The video encourages viewers to share their thoughts on the SRN1 mechanism and to practice the mechanism for potential test questions.
Q & A
What decade was marked by advancement in oxidation reactions, and what did Daniel Sr develop during this time?
-The 1970s was the decade marked by advancements in oxidation reactions. Daniel Sr developed a method that became a staple in organic chemistry courses during this period.
What is the SRN1 reaction and why is it significant in organic chemistry?
-The SRN1 reaction is a type of nucleophilic substitution reaction that proceeds through a radical intermediate. It is significant in organic chemistry because it is a commonly taught mechanism and is often tested in exams.
What is the first step in the SRN1 reaction mechanism as described in the script?
-The first step in the SRN1 reaction mechanism involves a nucleophilic attack from DMSO onto the oxal chloride functional group, resulting in a tetrahedral intermediate with a negative charge on the oxygen atom.
How is the sulphonium ion formed in the SRN1 reaction?
-The sulphonium ion is formed by reacting DMSO with oxal chloride, followed by an attack by the released chloride anion, leading to the formation of dimethyl chlorosulfonium chloride.
What are some alternative methods to form the sulphonium ion other than using oxal chloride?
-Alternative methods to form the sulphonium ion include the reaction of dimethyl sulfide with chlorine or with NCS (N-chlorosuccinimide), among other possible reactions.
Why might some chemists prefer alternative methods to form the sulphonium ion, despite the common method being well-known?
-Some chemists might prefer alternative methods due to the unpleasant smell and handling difficulties associated with reagents like oxal chloride and dimethyl sulfide.
What is the role of the alcohol in the SRN1 reaction?
-In the SRN1 reaction, the alcohol acts as a nucleophile in an SN2 reaction, displacing the chlorine in the sulphonium ion to form an intermediate.
What is the typical base used in the SRN1 reaction, and what is its function?
-The typical base used in the SRN1 reaction is triethylamine. Its function is to deprotonate the methyl group attached to the sulfur atom, facilitating an intramolecular proton transfer to yield the final product.
Why is it incorrect to show the deprotonation step in the SRN1 reaction as immediately targeting the alpha hydrogens?
-Research data indicates that the correct mechanism involves triethylamine first deprotonating the methyl group attached to sulfur, followed by an intramolecular proton transfer, rather than directly targeting alpha hydrogens.
What are the chemical outcomes of the SRN1 reaction for primary and secondary alcohols, as illustrated in the script?
-In the SRN1 reaction, primary alcohols are oxidized to aldehydes, while secondary alcohols are oxidized to ketones. Ether functional groups remain unchanged.
How does the SRN1 reaction affect other functional groups in a molecule, such as double bonds or ethers?
-The SRN1 reaction specifically targets alcohols for oxidation and does not affect other functional groups like double bonds or ethers, leaving them intact.
Outlines
🧪 SRN1 Reaction Mechanism Overview
This paragraph introduces the SRN1 (Sulfur-Raney Nickel) reaction, a staple in organic chemistry courses during the 1970s. It discusses the development of Daniel Sr's method and the emergence of DMSO-based methods. The SRN1 reaction is highlighted as the most favored by textbook authors. The video aims to explain the SRN1 mechanism, focusing on the formation of the sulfonium cation through a nucleophilic attack involving DMSO and oxal chloride, leading to a series of electron rearrangements and the release of byproducts like carbon monoxide and carbon dioxide. The paragraph emphasizes the complexity of this part of the mechanism and the importance of practicing it for exams. It also mentions alternative methods for forming the sulfonium ion, such as using dimethyl sulfide with chlorine or NCS, and acknowledges the unpleasant smell associated with these chemicals.
📚 SRN1 Reaction Applications and Test Preparation
The second paragraph delves into the practical applications of the SRN1 reaction, highlighting its excellent chemical activity in oxidizing primary alcohols without affecting other functional groups like alkenes or ethers. It provides examples of how the reaction behaves with different types of alcohols, such as primary and secondary alcohols, and the products formed as a result. The paragraph encourages viewers to practice the SRN1 reaction thoroughly due to its likelihood of appearing on exams. It also invites viewers to share their opinions on the reaction and thanks the Organic Chemistry Tutor members and sponsors for their support. The video concludes with a call to action for viewers to like, share, and subscribe for more organic chemistry content.
Mindmap
Keywords
💡SRN1 Mechanism
💡DMSO
💡Oxidation Reactions
💡Tetrahedral Intermediate
💡Nucleophilic Attack
💡Sulfonium Ion
💡Alcohol Oxidation
💡Triethylamine
💡Intramolecular Proton Transfer
💡Swern Oxidation
💡Organic Chemistry
Highlights
The 1970s saw advancements in oxidation reactions, with Daniel Sr developing a staple method in organic chemistry courses.
Many DMSO-based methods emerged during the same period, but the Swern oxidation gained prominence in organic chemistry textbooks.
Victor, an organic chemistry tutor, explains the Swern oxidation mechanism in a video tutorial.
The Swern oxidation proceeds in two phases, starting with the creation of a sulphonium cation.
DMSO reacts with oxal chloride to form the sulphonium ion through a nucleophilic attack and elimination steps.
The intermediate formed in the reaction undergoes a complex electron rearrangement to produce the dimethyl chlorosulfonium ion.
Alternative methods for forming the sulfonium ion include reactions with dimethyl sulfide and chlorine or with NCS.
The sulfonium ion reacts with an alcohol in an SN2 fashion, displacing the chlorine.
Deprotonation of the intermediate with triethylamine is followed by an intramolecular proton transfer to yield the final product.
Triethylamine is the preferred base for the deprotonation step, though other bases may also be used.
Some textbooks incorrectly show the immediate attack on alpha hydrogens, but research data supports a different pathway.
The Swern oxidation is a commonly tested mechanism in organic chemistry, and it's important to practice for exams.
The Swern oxidation has excellent chemoselectivity, as demonstrated by its ability to oxidize primary alcohols without affecting other functional groups.
Victor emphasizes the importance of understanding and practicing the Swern oxidation mechanism for success in organic chemistry.
The video includes examples of Swern oxidation with different types of alcohols and discusses the outcomes.
Victor thanks the viewers, especially the members and sponsors of Organic Chemistry Tutor, for their support.
Transcripts
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