science

Pyrazole

Pyrazole is a science 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 Pyrazole rather than just read about it. In short: Pyrazole is an organic compound with the formula (CH)3N2H. It is a heterocycle characterized as an azole with a 5-membered ring of three carbon atoms and two adjacent nitrogen atoms, which are in ortho-substitution.

Key takeaways

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

Reference excerpt

Pyrazole is an organic compound with the formula (CH)3N2H. It is a heterocycle characterized as an azole with a 5-membered ring of three carbon atoms and two adjacent nitrogen atoms, which are in ortho-substitution. Pyrazoles are also a class of compounds that have the ring C3N2 with adjacent nitrogen atoms. Pyrazole itself has few applications but many substituted pyrazoles are of commercial interest. Notable drugs containing a pyrazole ring are celecoxib (celebrex) and the anabolic steroid stanozolol.

Properties Pyrazole is a weak base, with pKb 11.5 (pKa of the conjugate acid 2.49 at 25 °C). According to X-ray crystallography, the compound is planar. The two C-N distances are similar, both near 1.33 Å

History The term pyrazole was given to this class of compounds by German Chemist Ludwig Knorr in 1883. In a classical method developed by German chemist Hans von Pechmann in 1898, pyrazole was synthesized from acetylene and diazomethane.

Preparation Pyrazoles are synthesized by the reaction of α,β-unsaturated aldehydes with hydrazine and subsequent dehydrogenation:

Substituted pyrazoles are prepared by condensation of 1,3-diketones with hydrazine (Knorr-type reactions). For example, acetylacetone and hydrazine gives 3,5-dimethylpyrazole:

CH3C(O)CH2C(O)CH3 + N2H4 → (CH3)2C3HN2H + 2 H2O A wide variety of pyrazoles can be made so:

Occurrence and uses

In 1959, the first natural pyrazole, 1-pyrazolyl-alanine, was isolated from seeds of watermelons. In medicine, derivatives of pyrazole are widely used, including celecoxib and similar COX-2 inhibitors, zaleplon, betazole, and CDPPB. The pyrazole ring is found within a variety of pesticides as fungicides, insecticides and herbicides, including fluoxapiprolin, fenpyroximate, fipronil, tebufenpyrad and tolfenpyrad. Pyrazole moieties are listed among the highly used ring systems for small molecule drugs by the US FDA

3-(Difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid is used in the manufacture of six commercial fungicides which are inhibitors of succinate dehydrogenase. Pyrazole is an inhibitor of the alcohol dehydrogenase enzyme, and, as such, is used as an adjuvant with ethanol, to induce alcohol dependency in experimental laboratory mice.

Conversion to scorpionates Pyrazoles react with potassium borohydride to form a class of ligands known as scorpionate. Pyrazole itself reacts with potassium borohydride at high temperatures (~200 °C) to form a tridentate ligand known as Tp ligand:

See also 3,5-dimethylpyrazole Pyrazolidine, fully saturated analogue imidazole, structural analogue of pyrazole with two non-adjacent nitrogen atoms. isoxazole, another analogue, the nitrogen atom in position 1 replaced by oxygen.

References

Further reading A. Schmidt; A. Dreger (2011). "Recent Advances in the Chemistry of Pyrazoles. Part 2. Reactions and N-Heterocyclic Carbenes of Pyrazole". Curr. Org. Chem. 15 (16): 2897–2970. doi:10.2174/138527211796378497.

Illustrations

Worked examples

Example 1 — a first encounter with Pyrazole

Start with the simplest possible case. Write down what Pyrazole claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, 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 Pyrazole 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 Pyrazole 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 Pyrazole

In research: Pyrazole appears in science 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 Pyrazole 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: Pyrazole is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aromatic bases, Pyrazoles, Simple aromatic rings, so understanding it makes those chapters shorter.
In everyday life: Look for Pyrazole 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 Pyrazole in 20 minutes

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

Frequently asked questions

What is Pyrazole in simple terms?

Why does Pyrazole matter?

Because it connects several science 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 Pyrazole?

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 Pyrazole.