What Is 5-Chloro-3-methyl-1H-pyrazole?

5-Chloro-3-methyl-1H-pyrazole (CAS 5765-44-6, MW 116.55 g/mol, formula C₄H₅ClN₂) is a five-membered nitrogen-containing heterocycle belonging to the pyrazole class. The ring bears a chlorine substituent at the 5-position and a methyl group at the 3-position, with an N–H tautomer in equilibrium with the 3-chloro-5-methyl form. This tautomerism is a well-established feature of monosubstituted 1H-pyrazoles and is important to consider when interpreting NMR spectra or designing downstream reactions.

The compound is supplied by Aladdin Scientific under SKU C174584 as a white to off-white crystalline solid. It is a versatile electrophilic building block, where the C–Cl bond can be exploited in nucleophilic aromatic substitution, palladium-catalysed cross-coupling, and condensation reactions, while the N–H provides a handle for N-alkylation or N-acylation.

Handling, Storage, and Safety

Although 5-chloro-3-methyl-1H-pyrazole is a solid at room temperature, researchers should treat it as a potentially irritating chemical and work in a well-ventilated fume hood wearing appropriate personal protective equipment (nitrile gloves, lab coat, safety goggles). Avoid generating dust during weighing.

For storage, keep the reagent in a tightly sealed container away from moisture and strong oxidising agents. A cool, dry environment (typically 2–8 °C or room temperature under inert atmosphere, depending on the supplier's certificate of analysis) is recommended to maintain long-term stability. Always consult the Safety Data Sheet (SDS) supplied with the product for GHS hazard classifications, first-aid measures, and disposal guidance before use.

Disposal: Do not dispose of chlorinated heterocyclic compounds via drain or general waste. Follow institutional and local regulations for halogenated organic waste.

Research and Synthetic Applications

5-Chloro-3-methyl-1H-pyrazole is a high-value intermediate in medicinal chemistry and agrochemical research. Its principal uses include:

• Pharmaceutical synthesis: The chloropyrazole scaffold appears in inhibitors targeting kinases, phosphodiesterases, and other enzymes. The C5–Cl bond allows selective introduction of amine, alkoxy, or aryl groups via S_NAr or transition-metal catalysis.
• Agrochemical intermediates: Chloromethylpyrazole derivatives serve as key building blocks in the synthesis of herbicides, fungicides, and insecticides.
• Material science: Pyrazole-based ligands with halogen substituents are used in the preparation of coordination polymers and metal-organic frameworks (MOFs).
• Fragment-based drug discovery: The small, rigid, heteroaromatic structure makes it suitable as a fragment hit for further elaboration.

Researchers frequently use N-alkylation (to lock one tautomer) before engaging the C–Cl in cross-coupling, improving regioselectivity.

Purity, Quality, and Ordering Information

Aladdin Scientific supplies 5-chloro-3-methyl-1H-pyrazole under SKU C174584. Each lot is accompanied by a Certificate of Analysis (CoA) detailing purity (typically assessed by HPLC or GC), melting point, and spectroscopic identity confirmation (¹H NMR, MS). Customers are encouraged to download the CoA for their specific lot number from the Aladdin website or contact technical support.

If your application demands higher purity or a specific physical form (e.g., anhydrous, micronised), please contact Aladdin's sales team to discuss custom specifications. Bulk quantities may be available on request.

To order, search for C174584 on www.aladdin-e.com, add to cart, and proceed through the standard checkout. Institutional purchase orders are accepted. For questions on pricing, promotions, or reward points applicable to this SKU, contact customer service.