Chemical Identity and Properties

6-Chloro-3-hydroxypyridazine-4-carboxylic acid (CAS catalogued under Aladdin SKU C193634) is a bifunctional pyridazine derivative bearing three reactive sites: a chloro substituent at the 6-position, a hydroxyl group at the 3-position (which may exist in tautomeric equilibrium with the pyridazinone form), and a carboxylic acid at the 4-position.

Molecular formula: C₅H₃ClN₂O₃; molecular weight: 174.54 g/mol. The compound is a solid at room temperature. The coexistence of the hydroxypyridazine and pyridazinone tautomers is characteristic of 3-hydroxypyridazine derivatives and has implications for reactivity and hydrogen-bonding capacity in both solution and solid state.

The carboxylic acid functionality (pKa typically in the range of 2–4 for aromatic carboxylic acids; exact value not confirmed in source material — see review flags) confers moderate acidity and enables salt formation with bases, which can be exploited for purification or formulation purposes.

Safety and Handling

General precautions: Although specific GHS hazard classification data for 6-Chloro-3-hydroxypyridazine-4-carboxylic acid was not provided in the source material (see review flags), standard laboratory safety practices for fine chemical intermediates must be followed.

• Wear appropriate personal protective equipment (PPE): nitrile gloves, safety glasses, and a laboratory coat at minimum.
• Handle in a well-ventilated fume hood to avoid inhalation of dust or aerosols.
• Avoid contact with skin, eyes, and mucous membranes.
• Wash hands thoroughly after handling.

First aid: In case of skin contact, wash with soap and water for at least 15 minutes. In case of eye contact, rinse immediately with copious water and seek medical attention. If inhaled, move to fresh air.

Disposal: Dispose of waste in accordance with local, regional, and national regulations applicable to halogenated organic compounds. Do not pour down the drain without verification of local disposal codes.

Solubility and Solution Preparation

Precise solubility data for 6-Chloro-3-hydroxypyridazine-4-carboxylic acid in specific solvents was not provided in the source material; the following guidance is based on the compound's chemical class and functional group composition (see review flags).

Recommended solvents (typical for hydroxypyridazine carboxylic acids):

• DMSO: Generally a good primary solvent for polar heterocyclic carboxylic acids. Prepare a 10–50 mM stock solution. Warm gently (37 °C water bath) and vortex if dissolution is slow.
• Aqueous base (0.1 M NaOH or Na₂CO₃): The carboxylic acid can be deprotonated to form a water-soluble sodium salt. Adjust pH to 7–8 after dissolution if required for biological assays.
• Methanol or ethanol: May offer partial solubility; suitable for analytical or chromatographic applications.
• Water alone: Limited solubility expected due to the hydrophobic pyridazine ring; not recommended for concentrated stock solutions.

Protocol for stock solution preparation in DMSO:

1. Weigh the required mass of compound into a clean, dry glass vial using an analytical balance.
2. Add anhydrous DMSO to achieve the target concentration (e.g., 10 mM for a 174.54 g/mol compound: dissolve 1.75 mg in 1 mL DMSO).
3. Cap the vial, vortex for 60 seconds, then sonicate for 5 minutes if needed.
4. Visually confirm complete dissolution before use. Filter through a 0.22 µm PTFE syringe filter if sterility or particle removal is required.
5. Store aliquots at –20 °C to minimize DMSO absorption of moisture and compound degradation.

Applications in Synthetic Chemistry

6-Chloro-3-hydroxypyridazine-4-carboxylic acid serves as a multifunctional heterocyclic building block exploitable through each of its three reactive handles:

1. Nucleophilic aromatic substitution (SNAr) at C-6: The electron-withdrawing carboxylic acid and ring nitrogen atoms activate the C–Cl bond toward displacement by amines, alkoxides, and thiolates, enabling rapid diversification of the pyridazine scaffold.

2. Carboxylic acid derivatization: Activation with coupling reagents (e.g., HATU, EDC/NHS, or thionyl chloride) converts the –COOH group to amides, esters, or acid chlorides, facilitating conjugation to drug candidates, linkers, or solid supports.

3. Hydroxyl/pyridazinone reactivity: The C-3 hydroxyl (pyridazinone tautomer) can participate in O-alkylation or O-acylation reactions, or act as a chelating group in coordination chemistry for metal-binding studies.

This scaffold is structurally relevant to pyridazinone-based pharmacophores that appear in inhibitors of phosphodiesterases, kinases, and other enzyme targets. It may also serve as a precursor to herbicidal compounds in agrochemical synthesis programs. Researchers are advised to consult the primary literature for specific reaction conditions and yields.

Storage, Stability, and Quality Control

Storage conditions: Store at 2–8 °C in a tightly sealed container, protected from light and atmospheric moisture. For long-term archival storage, consider –20 °C under inert gas (argon or nitrogen) to prevent oxidative or hydrolytic degradation of the carboxylic acid and chloro functionalities.

Stability considerations: Halogenated pyridazine carboxylic acids may be susceptible to slow hydrolysis of the C–Cl bond under prolonged exposure to strongly nucleophilic aqueous conditions. The carboxylic acid group is generally stable under neutral to mildly acidic conditions. Specific stability data for this compound under various conditions was not provided in the source material (see review flags).

Quality control upon receipt:

• Inspect the container for integrity and compare the physical appearance (color, texture) with the certificate of analysis (CoA) provided by Aladdin Scientific.
• Verify identity by ¹H NMR or LC-MS if an in-house analytical capability is available.
• Check purity by HPLC (reverse-phase C18 column, UV detection at 254 nm or 280 nm) against the CoA specification.
• Record the date of opening and initial mass; re-weigh periodically to detect moisture uptake.

Shelf life: Consult the product CoA and label for the manufacturer-stated expiry date. Contact Aladdin Scientific customer service (SKU C193634) for re-testing or custom purity verification services.