2-Chloro-5-Nitropyrimidine: Properties, Synthesis & Applications

2-Chloro-5-nitropyrimidine is a halogenated, electron-deficient heterocyclic compound widely used as a reactive building block in the synthesis of pharmaceuticals, agrochemicals, and functional materials.

CAS Number

4529-11-7

Molecular Formula

C₄H₂ClN₃O₂

Molecular Weight

159.53 g/mol

Appearance

Light yellow to yellow crystalline solid

Key Functional Groups

Chloro (C-2), Nitro (C-5) on pyrimidine ring

Primary Reactivity

Nucleophilic aromatic substitution (SNAr) at C-2

Chemical Structure and Properties

2-Chloro-5-nitropyrimidine (CAS 4529-11-7) belongs to the pyrimidine family of diazine heterocycles, featuring a six-membered aromatic ring with nitrogen atoms at positions 1 and 3. The compound bears two strongly electron-withdrawing substituents: a chloro group at the 2-position and a nitro group at the 5-position. This combination renders the ring highly electron-deficient, significantly lowering the LUMO energy and activating the ring toward nucleophilic attack.

The molecular formula is C₄H₂ClN₃O₂ with a molecular weight of approximately 159.53 g/mol. The compound is typically obtained as a light yellow to yellow crystalline solid. Its high degree of ring activation makes it considerably more reactive in nucleophilic aromatic substitution (SNAr) reactions than simpler chloropyrimidines or chlorobenzenes, which is a key reason for its broad utility in synthetic chemistry.

Reactivity and Key Synthetic Transformations

The dominant reaction pathway for 2-Chloro-5-nitropyrimidine is nucleophilic aromatic substitution (SNAr) at the C-2 chloro position. The electron-withdrawing nitro group at C-5 synergizes with the ring nitrogen atoms to stabilize the Meisenheimer complex intermediate, facilitating displacement of the chloride by a wide range of nucleophiles including amines, alcohols, thiols, and organometallic reagents.

Common transformations include:

• Amination: Reaction with primary or secondary amines yields 2-amino-5-nitropyrimidine derivatives, key scaffolds in medicinal chemistry.
• Alkoxylation: Treatment with alkoxides or phenols under mild base conditions introduces ether linkages at C-2.
• Thioetherification: Thiols react efficiently to provide thioether-linked pyrimidines.
• Cross-coupling: The chloro substituent can also participate in palladium-catalyzed cross-coupling reactions (e.g., Suzuki, Buchwald-Hartwig) for C–C and C–N bond formation.

Following SNAr, the resulting nitro group can be further reduced to an amine, providing an additional handle for functionalization, thus making 2-Chloro-5-nitropyrimidine a bifunctional synthetic linchpin.

Applications in Pharmaceutical and Agrochemical Research

2-Chloro-5-nitropyrimidine serves as a versatile intermediate in the synthesis of biologically active molecules. In medicinal chemistry, the pyrimidine core is a privileged scaffold found in numerous approved drugs and drug candidates targeting kinases, dihydrofolate reductase (DHFR), and other enzymes. The electron-deficient character of 2-Chloro-5-nitropyrimidine makes it particularly useful for rapid library synthesis via parallel SNAr reactions with amine collections.

Representative pharmaceutical applications include the preparation of:

• Kinase inhibitor scaffolds bearing aminopyrimidine motifs
• Antiparasitic and antimicrobial agents based on nitroheterocyclic pharmacophores
• DHFR inhibitors and antifolate compounds

In agrochemical research, nitropyrimidine derivatives have been explored as herbicides, fungicides, and insecticides. The ease of diversification at C-2 allows rapid structure-activity relationship (SAR) studies across both pharmaceutical and crop-protection programs.

Handling, Storage, and Safety Considerations

As with all nitroaromatic and halogenated heterocyclic compounds, appropriate safety precautions must be observed when handling 2-Chloro-5-nitropyrimidine. The compound should be treated as a potential irritant to skin, eyes, and the respiratory tract. Personnel should use appropriate personal protective equipment (PPE) including lab coat, chemical-resistant gloves, and safety glasses, and should work in a well-ventilated fume hood.

For storage, the compound should be kept in a tightly sealed container away from light, moisture, and heat in a cool, dry environment. It should be stored separately from strong oxidizing agents, bases, and reducing agents. Users should consult the current Safety Data Sheet (SDS) provided by Aladdin Scientific for comprehensive hazard information, first-aid measures, and disposal guidelines prior to use.

Waste disposal must comply with local and institutional regulations governing halogenated and nitro-containing organic waste streams.

Frequently asked questions

What makes 2-Chloro-5-nitropyrimidine more reactive than 2-chloropyrimidine in SNAr reactions?

The nitro group at the 5-position is a powerful electron-withdrawing group that further depletes electron density from the ring, especially at the positions ortho and para to itself. In combination with the ring nitrogen atoms, this strongly stabilizes the anionic Meisenheimer complex transition state, substantially lowering the activation energy for nucleophilic displacement of the C-2 chloride compared to unsubstituted 2-chloropyrimidine.

Can the nitro group of 2-Chloro-5-nitropyrimidine be selectively reduced after SNAr functionalization?

Yes. After nucleophilic substitution at C-2, the nitro group at C-5 can be selectively reduced to an amine using standard methods such as catalytic hydrogenation (H₂/Pd-C), iron or zinc in acidic conditions, or sodium dithionite. The resulting 5-amino group provides a valuable additional site for further acylation, reductive amination, or diazotization, greatly expanding the structural diversity accessible from this starting material.

What solvents and conditions are typically used for SNAr reactions with 2-Chloro-5-nitropyrimidine?

SNAr reactions with 2-Chloro-5-nitropyrimidine are commonly performed in polar aprotic solvents such as DMF, DMSO, acetonitrile, or THF. For amine nucleophiles, an organic base such as triethylamine or N,N-diisopropylethylamine (DIPEA) is typically used to neutralize the HCl generated. Reactions often proceed efficiently at room temperature to 80 °C depending on the nucleophile's reactivity. Alcohol and thiol nucleophiles generally require base (e.g., K₂CO₃) to generate the corresponding alkoxide or thiolate prior to reaction.

How should 2-Chloro-5-nitropyrimidine be stored to maintain its stability?

The compound should be stored as a solid in a tightly closed container under cool, dry, and dark conditions. Exposure to moisture, light, and elevated temperatures should be avoided to prevent hydrolysis or decomposition. Always consult the Aladdin Scientific SDS for the most current storage recommendations and stability data.

References

1. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry, 2nd ed.; Oxford University Press: Oxford, 2012. Chapter on nucleophilic aromatic substitution.
2. Joule, J. A.; Mills, K. Heterocyclic Chemistry, 5th ed.; Wiley-Blackwell: Oxford, 2010. Pyrimidine reactivity and synthesis.
3. Aladdin Scientific. Product Safety Data Sheet: 2-Chloro-5-nitropyrimidine, SKU C137950. Aladdin Scientific, current edition.

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