chemistry

Pyridinium chlorochromate

Pyridinium chlorochromate 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 Pyridinium chlorochromate rather than just read about it. In short: Pyridinium chlorochromate (PCC), also known as the Corey–Suggs reagent, is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for oxidation of alcohols to form carbonyls.

Key takeaways

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Reference excerpt

Pyridinium chlorochromate (PCC), also known as the Corey–Suggs reagent, is a yellow-orange salt with the formula [C5H5NH]+[CrO3Cl]−. It is a reagent in organic synthesis used primarily for oxidation of alcohols to form carbonyls. A variety of related compounds are known with similar reactivity. PCC offers the advantage of the selective oxidation of alcohols to aldehydes or ketones, whereas many other reagents are less selective.

Structure and preparation PCC consists of a pyridinium cation, [C5H5NH]+, and a tetrahedral chlorochromate anion, [CrO3Cl]−. Related salts are also known, such as 1-butylpyridinium chlorochromate, [C5H5N(C4H9)][CrO3Cl] and potassium chlorochromate. PCC is commercially available. Discovered by accident, the reagent was originally prepared via addition of pyridine into a cold solution of chromium trioxide in concentrated hydrochloric acid:

C5H5N + HCl + CrO3 → [C5H5NH][CrO3Cl] In one alternative method, formation of toxic chromyl chloride (CrO2Cl2) fumes during the making of the aforementioned solution were minimized by simply changing the order of addition: a cold solution of pyridine in concentrated hydrochloric acid was added to solid chromium trioxide under stirring.

Uses

Oxidation of alcohols PCC is used as an oxidant. In particular, it has proven to be highly effective in oxidizing primary and secondary alcohols to aldehydes and ketones, respectively. The reagent is more selective than the related Jones' Reagent, so there is little chance of over-oxidation to form carboxylic acids if acidified potassium permanganate is used as long as water is not present in the reaction mixture. A typical PCC oxidation involves addition of an alcohol to a suspension of PCC in dichloromethane. The general reaction is:

2 [C5H5NH][CrO3Cl] + 3 R2CHOH → 2 [C5H5NH]Cl + Cr2O3 + 3 R2C=O + 3 H2O For example, the triterpene lupeol was oxidized to lupenone:

Babler oxidation

With tertiary alcohols, the chromate ester formed from PCC can isomerize via a [3,3]-sigmatropic reaction and following oxidation yield an enone, in a reaction known as the Babler oxidation:

This type of oxidative transposition reaction has been synthetically utilized, e.g. for the synthesis of morphine. Using other common oxidants in the place of PCC usually leads to dehydration, because such alcohols cannot be oxidized directly.

Other reactions PCC also converts suitable unsaturated alcohols and aldehydes to cyclohexenones. This pathway, an oxidative cationic cyclization, is illustrated by the conversion of (−)-citronellol to (−)-pulegone. PCC also effects allylic oxidations, for example, in conversion of dihydrofurans to furanones.

Related reagents Other more convenient or less toxic reagents for oxidizing alcohols include dimethyl sulfoxide, which is used in Swern and Pfitzner–Moffatt oxidations, and hypervalent iodine compounds, such as the Dess–Martin periodinane.

Safety One disadvantage to the use of PCC is its toxicity, which it shares with other hexavalent chromium compounds.

See also Oxidation with chromium(VI)-amine complexes

References

Further reading Tojo, G.; Fernández, M. (2006). Tojo, G. (ed.). Oxidation of Alcohols to Aldehydes and Ketones: A Guide to Current Common Practice. Basic Reactions in Organic Synthesis. New York: Springer. ISBN 978-0-387-23607-0.

External links IARC Monographs Supplement 7, Chromium and Chromium Compounds History of PCC National Pollutant Inventory, Chromium(VI) Compounds Fact Sheets

Illustrations

Worked examples

Example 1 — a first encounter with Pyridinium chlorochromate

Start with the simplest possible case. Write down what Pyridinium chlorochromate 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 Pyridinium chlorochromate 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 Pyridinium chlorochromate 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 Pyridinium chlorochromate

In research: Pyridinium chlorochromate 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 Pyridinium chlorochromate 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: Pyridinium chlorochromate is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chromates, IARC Group 1 carcinogens, Oxidizing agents, so understanding it makes those chapters shorter.
In everyday life: Look for Pyridinium chlorochromate 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 Pyridinium chlorochromate in 20 minutes

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Frequently asked questions

What is Pyridinium chlorochromate in simple terms?

Why does Pyridinium chlorochromate 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 Pyridinium chlorochromate?

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 Pyridinium chlorochromate.