chemistry

Thiourea organocatalysis

Thiourea organocatalysis 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 Thiourea organocatalysis rather than just read about it. In short: Within the area of organocatalysis, (thio)urea organocatalysis describes the use of ureas and thioureas to accelerate and stereochemically alter organic transformations. The effects arise through hydrogen-bonding interactions between the substrate and the (thio)urea.

Key takeaways

Thiourea organocatalysis belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Thiourea organocatalysis to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thiourea organocatalysis from memory before moving on to harder problems.

Reference excerpt

Within the area of organocatalysis, (thio)urea organocatalysis describes the use of ureas and thioureas to accelerate and stereochemically alter organic transformations. The effects arise through hydrogen-bonding interactions between the substrate and the (thio)urea. Unlike classical catalysts, these organocatalysts interact by non-covalent interactions, especially hydrogen bonding ("partial protonation"). The scope of these small-molecule H-bond donors termed (thio)urea organocatalysis covers both non-stereoselective and stereoselective reactions.

Catalyst-substrate interactions Hydrogen-bonding between thiourea derivatives and carbonyl substrates involve two hydrogen bonds provided by coplanar amino substituents in the (thio)urea. Squaramide catalysts engage in double H-bonding interactions and are often superior to thioureas. Thioureas are often found to be stronger hydrogen-bond donors (i.e., more acidic) than ureas because their amino groups are more positively charged. Quantum chemical analyses revealed that this counterintuitive phenomenon, which is not explainable by the relative electronegativities of O and S, results from the effective steric size of the chalcogen atoms.

Advantages of thiourea organocatalysts （Thio) ureas are green and sustainable catalysts. When effective, they can offer these advantages:

absence of product inhibition due to weak enthalpic binding, but specific binding-"recognition" simple and inexpensive synthesis from primary amine functionalized (chiral-pool) starting materials and isothiocyanates easy to modulate and to handle (bench-stable), no inert gas atmosphere required catalysis under almost neutral conditions (pka thiourea 21.0) and mild conditions, acid-sensitive substrates are tolerated metal-free, nontoxic (compare traditional metal-containing Lewis-acid catalysts) water-tolerant, even catalytically effective in water or aqueous media.

Substrates H-bond accepting substrates include carbonyl compounds, imines, nitroalkenes. The Diels-Alder reaction is one process that can benefit from (thio)urea catalysts.

History Early contributions were made by Kelly, Etter, Jorgensen, Hine, Curran, Göbel, and De Mendoza (see review articles cited below) on hydrogen bonding interactions of small, metal-free compounds with electron-rich binding sites. Peter R. Schreiner and co-workers identified and introduced electron-poor thiourea derivatives as hydrogen-bonding organocatalysts. Schreiner's thiourea, N,N'-bis3,5-bis(trifluormethyl)phenyl thiourea, combines all structural features for double H-bonding mediated organocatalysis:

electron-poor rigid structure non-coordinating, electron withdrawing substituents in 3,4, and/or 5 position of a phenyl ring the 3,5-bis(trifluoromethyl)phenyl-group is the preferred substituent

Catalysts A broad variety of monofunctional and bifunctional (concept of bifunctionality) chiral double hydrogen-bonding (thio)urea organocatalysts have been developed.

See also Organocatalysis Hydrogen-bond catalysis Squaramide catalysis

Further reading Christian M. Kleiner, Peter R. Schreiner (2006). "Hydrophobic amplification of noncovalent organocatalysis". Chem. Commun.: 4315–4017. Z. Zhang and P. R. Schreiner (2007). "Thiourea-Catalyzed Transfer Hydrogenation of Aldimines". Synlett. 2007 (9): 1455–1457. doi:10.1055/s-2007-980349. Wanka, Lukas; Chiara Cabrele; Maksims Vanejews; Peter R. Schreiner (2007). "γ-Aminoadamantanecarboxylic Acids Through Direct C–H Bond Amidations". European Journal of Organic Chemistry. 2007 (9): 1474–1490. doi:10.1002/ejoc.200600975. ISSN 1434-193X.

References

Illustrations

Worked examples

Example 1 — a first encounter with Thiourea organocatalysis

Start with the simplest possible case. Write down what Thiourea organocatalysis 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 Thiourea organocatalysis 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 Thiourea organocatalysis 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 Thiourea organocatalysis

In research: Thiourea organocatalysis 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 Thiourea organocatalysis 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: Thiourea organocatalysis is common in secondary-school and first-year university syllabi. It links to neighbouring topics 3,5-bis(Trifluoromethyl)phenyl compounds, Catalysis, Ureas, so understanding it makes those chapters shorter.
In everyday life: Look for Thiourea organocatalysis 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 Thiourea organocatalysis in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thiourea organocatalysis 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.
Explain Thiourea organocatalysis out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thiourea organocatalysis in simple terms?

Why does Thiourea organocatalysis 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 Thiourea organocatalysis?

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 Thiourea organocatalysis.