6-Chloro-4-nitro-1H-indole: Handling & Use Protocol

6-Chloro-4-nitro-1H-indole is a halogenated, electron-deficient indole building block widely employed as a synthetic intermediate in medicinal chemistry, agrochemical research, and the preparation of functionalized heterocyclic scaffolds.

Chemical Name

6-Chloro-4-nitro-1H-indole

SKU

C728592

Molecular Formula

C₈H₅ClN₂O₂

Molecular Weight

196.59 g/mol

Appearance

Solid (expected pale to yellow powder)

Recommended Storage

Store at room temperature, away from light and moisture; seal tightly after use

Key Functional Groups

Nitro group (C-4), Chloro substituent (C-6), NH indole core

Scope and Intended Use

6-Chloro-4-nitro-1H-indole (Aladdin SKU C728592) is an electron-deficient indole derivative bearing both a nitro group at the 4-position and a chloro substituent at the 6-position. This combination of electron-withdrawing groups makes the ring system highly activated toward nucleophilic aromatic substitution (SNAr) and palladium-catalysed cross-coupling reactions (e.g., Suzuki–Miyaura, Buchwald–Hartwig). It serves primarily as a synthetic intermediate in:

• Medicinal chemistry programmes targeting kinase inhibitors, antifungal agents, and other bioactive heterocyclic scaffolds.
• Agrochemical research requiring functionalised indole cores.
• Material science applications involving nitrogen-containing aromatic systems.

This protocol covers receipt, storage, stock solution preparation, and general reaction setup guidance for laboratory personnel using this reagent.

Safety and Handling Precautions

General Hazard Assessment: As a nitroaromatic compound, 6-Chloro-4-nitro-1H-indole should be treated as a potential irritant and sensitiser. Always consult the Safety Data Sheet (SDS) prior to use.

• Personal Protective Equipment (PPE): Wear nitrile gloves, laboratory coat, and safety goggles at all times when handling the neat compound or its solutions.
• Ventilation: All weighing and solution preparation should be performed inside a well-ventilated fume hood to minimise inhalation of dust or vapours.
• Skin and Eye Contact: In case of contact, flush affected area immediately with copious amounts of water for at least 15 minutes and seek medical advice.
• Waste Disposal: Dispose of all waste materials in accordance with local institutional and governmental regulations for organic chemical waste. Do not pour solutions containing this compound down the drain.
• Stability: Nitroaromatic compounds may be sensitive to strong reducing agents, heat, or mechanical shock in concentrated or neat form. Avoid contact with strong bases, oxidisers, and metals.

Note: Specific GHS classification and LD₅₀ values are not confirmed in the available source material and should be verified from the product SDS (review flag applied).

Stock Solution Preparation

The following procedure describes preparation of a 100 mM stock solution for use in synthetic or biochemical assays. Scale as required.

1. Solvent Selection: 6-Chloro-4-nitro-1H-indole is expected to dissolve readily in polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and tetrahydrofuran (THF). Solubility in aqueous buffers is anticipated to be low due to the hydrophobic aromatic core. Verify solubility experimentally before use.
2. Calculate required mass: For a 100 mM solution in 1 mL DMSO: mass (mg) = 0.1 mmol × 196.59 g/mol = 19.66 mg.
3. Weighing: Tare a clean, dry 1.5 mL microcentrifuge tube on an analytical balance. Transfer approximately 19.66 mg of 6-Chloro-4-nitro-1H-indole into the tube using a microspatula inside a fume hood.
4. Dissolution: Add 1.00 mL of anhydrous DMSO using a calibrated micropipette. Vortex for 30–60 seconds. If the compound does not dissolve completely, sonicate in a water bath (ambient temperature) for 5 minutes. Avoid heating above 60 °C.
5. Clarification: Visually inspect the solution. If particulates remain, filter through a 0.22 µm PTFE syringe filter into a fresh vial.
6. Labelling and Storage: Label the vial with compound name, concentration, solvent, date of preparation, and operator initials. Store at −20 °C under inert atmosphere (argon or nitrogen) protected from light for long-term stability. For short-term use (≤1 week), storage at 4 °C is acceptable.

Disclaimer: Exact solubility data for this specific compound were not available in the source material. The solvent recommendations above are based on general physicochemical properties of halogenated nitroindoles. Experimental verification is required (review flag applied).

General Reaction Setup Guidelines

6-Chloro-4-nitro-1H-indole is typically utilised in the following reaction classes. These guidelines summarise best practices; always consult primary literature for specific conditions.

Nucleophilic Aromatic Substitution (SNAr) at C-6

The electron-withdrawing nitro group at C-4 activates the C-6 chloro substituent toward displacement by soft nucleophiles (amines, thiols, alkoxides).

• Typical solvent: DMF or DMSO at 60–120 °C.
• Base: K₂CO₃ or Cs₂CO₃ (2–3 equiv).
• Monitor reaction progress by TLC or HPLC.

Palladium-Catalysed Cross-Coupling

The C-6 C–Cl bond can participate in Suzuki–Miyaura, Negishi, or Buchwald–Hartwig couplings under standard conditions.

• Catalyst: Pd(PPh₃)₄ or Pd(dppf)Cl₂ (2–5 mol%).
• Base: K₂CO₃ or Cs₂CO₃ in dioxane/water or DMF.
• Temperature: 80–100 °C under inert atmosphere.

N-Alkylation / N-Protection

The NH group may be protected or alkylated prior to further functionalisation using standard methods (NaH/alkyl halide in DMF, or Boc₂O/DMAP).

Analytical Monitoring: Confirm product identity by ¹H NMR, ¹³C NMR, and high-resolution mass spectrometry (HRMS). Purity should be assessed by HPLC (≥95% for biological testing).

Note: Specific literature examples citing this exact compound in published reactions were not available in the source material. Reaction conditions above are based on general indole and nitroaromatic chemistry principles (review flag applied).

Troubleshooting

Problem	Likely Cause	Suggested Action
Incomplete dissolution in DMSO	Insufficient mixing or degraded material	Vortex longer; sonicate briefly; check expiry and appearance of solid
Colour change of solution over time	Oxidation or light-induced degradation	Store in amber vials under inert gas; prepare fresh solutions
Low SNAr conversion	Insufficient temperature or base equivalents	Increase temperature incrementally; add additional base; switch to Cs₂CO₃
Low coupling yield (Pd reactions)	Catalyst poisoning or moisture	Use freshly activated molecular sieves; ensure anhydrous solvent; increase catalyst loading
NH deprotonation side reactions	Strongly basic conditions	Protect NH group before introducing strong base; use milder conditions

Frequently asked questions

What solvents are recommended for dissolving 6-Chloro-4-nitro-1H-indole?

Based on the physicochemical properties of halogenated nitroindoles, polar aprotic solvents such as DMSO, DMF, and THF are recommended. Solubility in water or aqueous buffers is expected to be low. Always verify solubility experimentally before use in assays.

How should 6-Chloro-4-nitro-1H-indole be stored to maintain stability?

The compound should be stored as a solid at room temperature or below, protected from light and moisture in a tightly sealed container. For long-term storage of solutions, −20 °C under inert atmosphere (argon or nitrogen) in amber vials is recommended. Avoid repeated freeze-thaw cycles.

What is the Aladdin SKU for 6-Chloro-4-nitro-1H-indole?

6-Chloro-4-nitro-1H-indole is available from Aladdin Scientific under SKU C728592. Please refer to the product page for current pricing, pack sizes, and availability.

Is 6-Chloro-4-nitro-1H-indole suitable for N-alkylation reactions?

Yes, the free NH group of 6-Chloro-4-nitro-1H-indole can be alkylated or protected using standard methods, such as treatment with NaH and an alkyl halide in DMF, or Boc-protection using Boc₂O and DMAP. N-protection is often advisable before performing reactions that require strongly basic conditions to prevent undesired side reactions.

Can the C-6 chloro group undergo palladium-catalysed cross-coupling?

Yes, the C–Cl bond at the 6-position is amenable to palladium-catalysed cross-coupling reactions, including Suzuki–Miyaura (with boronic acids), Negishi, and Buchwald–Hartwig amination. Standard catalysts such as Pd(PPh₃)₄ or Pd(dppf)Cl₂ at 2–5 mol% loading, with K₂CO₃ or Cs₂CO₃ as base in dioxane or DMF at 80–100 °C under inert atmosphere, are typical starting conditions.

References

1. Aladdin Scientific product page: 6-Chloro-4-nitro-1H-indole, SKU C728592.
2. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. 4th ed. Wiley, 1992. (General reference for SNAr and cross-coupling methodology.)
3. Clayden, J.; Greeves, N.; Warren, S. Organic Chemistry. 2nd ed. Oxford University Press, 2012. (General reference for indole chemistry and N-protection strategies.)

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.