3-Chloro-1-methyl-1H-pyrazole
[CAS 63425-54-7]

Identification

• Classification: Organic raw materials >> Heterocyclic compound
• Name: 3-Chloro-1-methyl-1H-pyrazole
• Synonyms: 3-Chloro-1-methylpyrazole
• Molecular Formula: C₄H₅ClN₂
• Molecular Weight: 116.55
• CAS Registry Number: 63425-54-7
• EC Number: 692-071-5
• SMILES: CN1C=CC(=N1)Cl

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Boiling point: 159.4±13.0 °C 760 mmHg (Calc.)^*
• Flash point: 50.2±19.8 °C (Calc.)^*
• Index of refraction: 1.563 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H302-H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P270-P271-P280-P301+P317-P302+P352-P304+P340-P305+P351+P338-P319-P321-P330-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H335
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2A	H319
Eye irritation	Eye Irrit.	2	H319

chemBlink Chemical Story

A short heterocyclic name can encode a useful synthetic plan. 3-Chloro-1-methyl-1H-pyrazole, CAS 63425-54-7, contains a five-membered aromatic ring with two adjacent nitrogen atoms. A methyl group is attached to one nitrogen, and chlorine occupies carbon 3. The specified positions distinguish it from other chlorinated methylpyrazoles with the same overall formula.

The N-methyl group is a permanent part of this particular structure, rather than an unmentioned protecting group. It removes the N-H site present in an unsubstituted pyrazole and helps define which ring nitrogen carries the substituent. The remaining carbon positions provide opportunities for further modification, but their reactivity must be established in an actual transformation rather than inferred from the presence of chlorine alone.

A concrete example appears in patent WO2010139731A1, concerning imidazoquinolinone derivatives. Its experimental sequence uses 3-chloro-1-methylpyrazole to obtain a nitro derivative at carbon 4, then converts that group into an amino group. The resulting amino-substituted pyrazole participates in the construction of more elaborate molecules. The sequence provides a documented role for the starting heterocycle without assigning the final compounds' biological properties to it.

The example is informative because the chlorine remains part of the pyrazole fragment while another ring position is elaborated. A halogenated building block is not useful only when its carbon-halogen bond is replaced. Sometimes one substituent is deliberately retained as other functionality is introduced nearby. That choice helps define the substitution pattern of the eventual molecular fragment.

This makes the compound's story one of positional control. Starting from a small ring whose nitrogen substitution is already specified, chemists can build a more functionalized fragment through a recorded sequence. The value lies in access to that precise arrangement. It does not establish that every chloro-methylpyrazole will follow the same route or that the starting material is itself a therapeutic agent.

References:
1. PubChem. 3-Chloro-1-methyl-1H-pyrazole; CAS 63425-54-7; CID 13630086. https://pubchem.ncbi.nlm.nih.gov/compound/13630086
2. WO2010139731A1. 1H-Imidazo[4,5-c]quinolinone derivatives; stages K.2 and K.1 document elaboration of 3-chloro-1-methylpyrazole. https://patents.google.com/patent/WO2010139731A1/en

Read more stories