Overview and Chemical Properties

5,6-Dichloro-2-methylpyridazin-3(2H)-one (SKU D726794) is a six-membered nitrogen-containing heterocyclic compound belonging to the pyridazinone family. The molecule features a pyridazin-3(2H)-one core bearing two chlorine substituents at positions 5 and 6, and an N-methyl group at position 2. The electron-withdrawing chlorine atoms activate the ring toward nucleophilic aromatic substitution (SNAr), making the compound a valuable electrophilic building block.

The compound is typically a solid at room temperature. Its pyridazinone scaffold is well-represented in pharmacologically active molecules, including antifungal, herbicidal, and kinase-inhibitory agents. The dual chloro substituents provide orthogonal handles for sequential functionalization, enabling selective mono- or di-substitution depending on reaction conditions.

Safety and Storage Guidelines

Personal Protective Equipment (PPE): Handle 5,6-Dichloro-2-methylpyridazin-3(2H)-one wearing nitrile gloves, a laboratory coat, and safety glasses. Work in a well-ventilated fume hood to avoid inhalation of dust or vapors. Chlorinated heterocycles may be irritating to skin, eyes, and the respiratory tract.

Storage: Store the compound in a tightly sealed container in a cool, dry location away from direct light and moisture. Unless the product datasheet specifies otherwise, storage at room temperature (15–25 °C) or under refrigeration (2–8 °C) is recommended. Keep away from incompatible materials such as strong oxidizers, bases, and reactive nucleophiles to prevent unintended substitution reactions.

Disposal: Dispose of waste material in accordance with local, institutional, and national regulations for halogenated organic compounds. Do not pour down the drain without appropriate treatment.

Solubility and Solution Preparation

Recommended Solvents: 5,6-Dichloro-2-methylpyridazin-3(2H)-one is expected to show good solubility in polar aprotic solvents such as dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and acetonitrile. Limited solubility is anticipated in water and aliphatic hydrocarbons. Always verify solubility empirically before large-scale use.

Stock Solution Preparation:

1. Equilibrate the sealed vial to room temperature before opening to minimise moisture absorption.
2. Weigh the desired amount of compound using a calibrated analytical balance.
3. Transfer to a clean, dry glass vial and add the appropriate volume of solvent to achieve the target concentration.
4. Vortex or sonicate briefly until complete dissolution is confirmed visually.
5. Filter through a 0.2 µm PTFE syringe filter if particulates are present.
6. Aliquot and store according to the storage conditions above. Avoid repeated freeze–thaw cycles.

Note: Prepare fresh solutions where possible, as hydrolysis of the C–Cl bonds may occur over extended periods in protic solvents.

Synthetic Applications and Reaction Protocol

The two C–Cl bonds of 5,6-Dichloro-2-methylpyridazin-3(2H)-one can be selectively displaced by nucleophiles via SNAr reactions. The C-6 position (adjacent to the ring nitrogen at N-1) is typically more electrophilic than C-5 and may react preferentially under mild conditions. Representative transformations include:

• Amination: React with primary or secondary amines (1–2 equivalents) in DMF or acetonitrile at 0 °C to room temperature to achieve selective mono-amination at C-6.
• Thioetherification: Treat with thiol nucleophiles in the presence of a mild base (e.g., K₂CO₃) in DMF.
• Cross-coupling: The C–Cl bonds may be amenable to Pd-catalysed cross-coupling reactions (e.g., Suzuki, Buchwald–Hartwig) under standard conditions.

General SNAr Procedure:

1. Charge a dry round-bottom flask with D726794 (1.0 equiv.) and dissolve in anhydrous DMF (0.2–0.5 M).
2. Add the nucleophile (1.05–1.2 equiv.) and base if required (1.5 equiv. K₂CO₃ or Et₃N).
3. Stir at the appropriate temperature (RT to 80 °C) and monitor by TLC or LC-MS.
4. Upon completion, quench with water, extract with ethyl acetate, wash the organic layer with brine, dry over MgSO₄, and concentrate.
5. Purify the product by column chromatography or recrystallisation.

Quality Control and Analytical Characterisation

Upon receipt, verify the identity and purity of 5,6-Dichloro-2-methylpyridazin-3(2H)-one (D726794) using the following techniques:

• ¹H NMR: Confirm the N-methyl singlet (~3.6 ppm) and the vinyl/aromatic proton at C-4. The ¹H NMR pattern should be consistent with a 1,2-disubstituted pyridazinone bearing two chlorines.
• ¹³C NMR and DEPT: Verify all ring carbons and the N-CH₃ carbon.
• HRMS or LC-MS: Confirm molecular ion consistent with C₅H₄Cl₂N₂O (MW 179.00); note the characteristic isotope pattern of two chlorine atoms (M:M+2:M+4 ≈ 9:6:1).
• HPLC Purity: An HPLC purity of ≥95% (UV 254 nm) is typically expected for research-grade material. Consult the Aladdin Certificate of Analysis (CoA) for the specific lot purity.
• Melting Point: Determine and compare with the reported value. Flag any significant deviation for further investigation.