chemistry

Pyridine-N-oxide

Pyridine-N-oxide 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 Pyridine-N-oxide rather than just read about it. In short: Pyridine-N-oxide is the heterocyclic compound with the formula C5H5NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine.

Key takeaways

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

Reference excerpt

Pyridine-N-oxide is the heterocyclic compound with the formula C5H5NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine. Its synthesis was first reported by Jakob Meisenheimer, who used peroxybenzoic acid as the oxidant. The compound is used infrequently as an oxidizing reagent in organic synthesis.

Structure The structure of pyridine-N-oxide is very similar to that of pyridine with respect to the parameters for the ring. The molecule is planar. The N–O distance is 1.34 Å. The C–N–C angle is 124°, 7° wider than in pyridine.

Synthesis The oxidation of pyridine can be achieved with a number of peroxy acids, including peracetic acid and peroxybenzoic acid. Oxidation can also be effected by a modified Dakin reaction using a urea–hydrogen peroxide complex, sodium perborate in acetic acid, catalytic methylrhenium trioxide (CH3ReO3) with sodium percarbonate or dimethyldioxirane.

Alternatively, glutaconaldehyde condenses with hydroxylamine to give pyridine N-oxide.

Reactions Pyridine N-oxide is five orders of magnitude less basic than pyridine: the pKa of protonated pyridine-N-oxide is 0.8. Protonated derivatives are nevertheless isolable, e.g., [C5H5NOH]Cl. Further demonstrating its (feeble) basicity, pyridine-N-oxide also serves as a ligand in coordination chemistry. A host of transition metal complexes of pyridine-N-oxides are known. Some electrophilic substitutions on pyridine rings are usefully effected using pyridine N-oxide followed by deoxygenation. The oxygen suppresses reaction at nitrogen atom and promotes substitution at the 2- and 4-carbons, particularly the 4 carbon. For example, 4-nitropyridine can be prepared from nitrating pyridine-N-oxide and subsequent deoxygenation with PCl3. Deoxygenation can also be carried out with POCl3 to give 2-chloropyridines.

The ortho and para positions of pyridine-N-oxide derivatives are also active in nucleophilic substitution to a Polonovski reaction-like product. Pyridine N-oxide is rather resistant to reduction. The electrochemical (half-wave) reduction potential is about -1.4 V relative to the saturated calomel electrode at neutral pH, rising to about -1.3 V at pH 3.5. For comparison, aliphatic and polyarene amine oxides are generally reduced between -0.2 and -0.8 V.

Related pyridine-N-oxides Pyridine-N-oxides are uncommon in nature. 2-(Methyldithio)pyridine-N-oxide and related compounds have been isolated from species of Allium. The N-oxides of various pyridines are precursors to useful drugs:

Nicotinic acid N-oxide, derived from nicotinic acid is a precursor to niflumic acid and pranoprofen. 2,3,5-Trimethylpyridine N-oxide is a precursor to the drug omeprazole 2-Chloropyridine N-oxide is a precursor to the fungicide zinc pyrithione

Safety The compound is a skin irritant.

Illustrations

Worked examples

Example 1 — a first encounter with Pyridine-N-oxide

Start with the simplest possible case. Write down what Pyridine-N-oxide 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 Pyridine-N-oxide 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 Pyridine-N-oxide 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 Pyridine-N-oxide

In research: Pyridine-N-oxide 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 Pyridine-N-oxide 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: Pyridine-N-oxide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Amine oxides, Oxidizing agents, Pyridinium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Pyridine-N-oxide 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 Pyridine-N-oxide in 20 minutes

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

Frequently asked questions

What is Pyridine-N-oxide in simple terms?

Pyridine-N-oxide is the heterocyclic compound with the formula C5H5NO. This colourless, hygroscopic solid is the product of the oxidation of pyridine.

Why does Pyridine-N-oxide 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 Pyridine-N-oxide?

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 Pyridine-N-oxide.