chemistry

Sulfonium-based oxidation of alcohols to aldehydes

Sulfonium-based oxidation of alcohols to aldehydes is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sulfonium-based oxidation of alcohols to aldehydes rather than just read about it. In short: Sulfonium-based oxidations of alcohols to aldehydes summarizes a group of organic reactions that transform a primary alcohol to the corresponding aldehyde (and a secondary alcohol to the corresponding ketone). Selective oxidation of alcohols to aldehydes requires circumventing over-oxidation to the carboxylic acid.

Key takeaways

Sulfonium-based oxidation of alcohols to aldehydes belongs to chemistry; place it in that map before memorising details.
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Reference excerpt

Sulfonium-based oxidations of alcohols to aldehydes summarizes a group of organic reactions that transform a primary alcohol to the corresponding aldehyde (and a secondary alcohol to the corresponding ketone). Selective oxidation of alcohols to aldehydes requires circumventing over-oxidation to the carboxylic acid. One popular approach are methods that proceed through intermediate alkoxysulfonium species (RO−SMe+2X-, e.g. compound 6) as detailed here. Since most of these methods employ dimethylsulfoxide (DMSO) as oxidant and generate dimethylsulfide, these are often colloquially summarized as DMSO-oxidations. Conceptually, generating an aldehyde and dimethylsulfide from an alcohol and DMSO requires a dehydrating agent for removal of H2O, ideally an electrophile simultaneously activating DMSO. In contrast, methods generating the sulfonium intermediate from dimethylsulfide do not require a dehydrating agent. Closely related are oxidations mediated by dimethyl selenoxide and by dimethyl selenide.

Comparison with related methods In comparisons, sulfonium-based methods are popular because reactions are efficient (high yields, comparably fast, no over-oxidation, few side reactions, reproducible results), reaction conditions are mild (low temperature, no strong acids or bases), reactions are operationally simple (no specialized equipment or uncommon and/or costly reagents necessary, byproducts often easily separated, tolerant of oxygen and moisture,) and they generally avoid highly toxic starting materials and toxic waste disposal. However, the reactions are not too popular with many undergraduate chemistry students in the laboratory since the common byproduct dimethylsulfide is a strong odorant, reminiscent of fouling eggs, that requires a well-ventilated fume hood. Other drawbacks might include excess of base, handling of the dehydrating agent, limited choice of solvent or side reactions at elevated temperature, e.g. Pummerer rearrangement or elimination of the sulfonium intermediate to the reactive H2C=(S+)-CH3-species that form methylthiomethyl ethers with alcohols. In consequence this means that the activity of the oxidation can not be tuned at will by increasing the reaction temperature, e.g. to force oxidation of an unreactive alcohol. Common alternatives to these sulfonium-based methods are oxidations with

hypervalent iodine (e.g., Dess-Martin periodinane, 2-Iodoxybenzoic acid) chromium reagents (e.g., Pyridinium chlorochromate, Collins reagent) ruthenium oxides (e.g., Tetrapropylammonium perruthenate) oxoammonium species (e.g., TEMPO) transfer hydrogenation or hydride transfer (e.g., Oppenauer oxidation) MnO2, Barium manganate, 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone for allylic alcohols

Categories The sulfonium oxidations can be categorized into two groups: The methods discovered earliest rely on activated alcohols like alkyl tosylates (Kornblum oxidation) or alkyl chloroformates (from reaction of alcohols with phosgene: Barton-Kornblum) that react as electrophiles when treated with DMSO, liberating an oxygenated leaving group (e.g. OTs−). However, the additional step for pre-activation of the alcohol and sometimes harsh reaction conditions for the nucleophilic displacement proved less convenient. Therefore, methods generating activated sulfoxides have been developed later. Depicted below is the activated sulfoxide generated during Swern oxidation 4 reacting with a secondary alcohol 5 to form alkoxysulfonium species 6. These activated sulfoxides react as electrophiles when treated with an alcohol, expelling a leaving group that might simultaneously function as counter-ion to the alkoxysulfonium species (RO−SMe+2) generated. Upon deprotonation – usually assisted by a mild base like triethylamine – the alkoxysulfonium species decomposes, yielding the aldehyde and dimethylsulfide. The latter collection contains popular oxidations like Swern, Corey-Kim, Parikh-Doering, Pfitzner-Moffatt and also includes Albright-Goldman, Albright-Onodera (DMSO/P2O5), TFAA/DMSO (Swern) and Me2S/Cl2. Recently, SO2F2 has been proposed for generating the activated sulfoxide from DMSO.

See also Alcohol oxidation Oxidation with chromium(VI)-amine complexes Oxoammonium-catalyzed oxidation Dess–Martin oxidation

References

Worked examples

Example 1 — a first encounter with Sulfonium-based oxidation of alcohols to aldehydes

Start with the simplest possible case. Write down what Sulfonium-based oxidation of alcohols to aldehydes claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sulfonium-based oxidation of alcohols to aldehydes before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sulfonium-based oxidation of alcohols to aldehydes ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sulfonium-based oxidation of alcohols to aldehydes

In research: Sulfonium-based oxidation of alcohols to aldehydes appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sulfonium-based oxidation of alcohols to aldehydes in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sulfonium-based oxidation of alcohols to aldehydes is common in secondary-school and first-year university syllabi. It links to neighbouring topics Organic oxidation reactions, so understanding it makes those chapters shorter.
In everyday life: Look for Sulfonium-based oxidation of alcohols to aldehydes outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sulfonium-based oxidation of alcohols to aldehydes in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sulfonium-based oxidation of alcohols to aldehydes means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Sulfonium-based oxidation of alcohols to aldehydes in simple terms?

Why does Sulfonium-based oxidation of alcohols to aldehydes matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sulfonium-based oxidation of alcohols to aldehydes?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sulfonium-based oxidation of alcohols to aldehydes.