Chemical Properties and Structure

4-(Methanesulfonyl)benzoyl chloride (CAS number should be verified; SKU B725791) is an aromatic acyl chloride in which the para position of the benzoyl chloride ring carries a methanesulfonyl (–SO₂CH₃) substituent. The molecular formula is C₈H₇ClO₃S with a molecular weight of approximately 218.66 g/mol.

The electron-withdrawing methanesulfonyl group deactivates the aromatic ring toward electrophilic aromatic substitution but simultaneously enhances the electrophilicity of the carbonyl carbon of the acyl chloride, increasing its reactivity toward nucleophilic acyl substitution. This dual functionality makes the compound particularly attractive as a bifunctional building block in medicinal chemistry and materials science.

The compound is typically a white to off-white crystalline solid or powder at room temperature. It is moisture-sensitive: exposure to water or humid air causes rapid hydrolysis of the acyl chloride to the corresponding carboxylic acid (4-(methanesulfonyl)benzoic acid) with evolution of hydrogen chloride gas.

Safe Handling, Storage, and Disposal

Personal Protective Equipment (PPE): Always handle 4-(Methanesulfonyl)benzoyl chloride in a well-ventilated fume hood. Wear chemically resistant gloves (e.g., nitrile or neoprene), safety goggles or a face shield, and a laboratory coat. The acyl chloride is a lachrymator and releases HCl upon contact with moisture; avoid inhalation of vapors or dust.

Storage: Store the reagent in a tightly sealed container under an inert atmosphere (nitrogen or argon) at 2–8 °C or as specified on the product label. Keep away from moisture, direct light, water, alcohols, and amines. Segregate from incompatible materials including bases, oxidizers, and reducing agents.

Spill and Disposal: In the event of a spill, neutralize carefully with dry sodium bicarbonate, avoiding the addition of water directly to the neat material. Collect in a sealed container and dispose of in accordance with local, national, and institutional regulations for halogenated organic waste. Do not pour down the drain. Consult your institution's Environmental Health & Safety (EHS) office for specific guidance.

First Aid: On skin contact, wash immediately with large amounts of water for at least 15 minutes and seek medical attention. On eye contact, flush with water for at least 15 minutes and seek immediate medical attention. If inhaled, move to fresh air immediately and seek medical advice.

Synthetic Applications and Reaction Protocols

4-(Methanesulfonyl)benzoyl chloride is widely employed in organic synthesis as an acylating agent. The highly electrophilic carbonyl, activated by the para-sulfonyl group, undergoes efficient nucleophilic acyl substitution with a broad range of nucleophiles:

• Amide formation: React with primary or secondary amines in the presence of a base (e.g., triethylamine, pyridine, or DIPEA) in anhydrous solvents such as DCM, THF, or DMF at 0 °C to room temperature. The amine acts as nucleophile; the base scavenges the HCl by-product.
• Ester formation: React with alcohols under similar base/anhydrous conditions to furnish aryl or alkyl esters.
• Sulfonamide-containing hybrid molecules: The intact sulfonyl group on the product allows further derivatization, for example displacement of the sulfonyl group or use as a pharmacophore in drug candidate synthesis.
• Friedel-Crafts acylation: In the presence of a Lewis acid catalyst (e.g., AlCl₃), the reagent can acylate activated aromatic substrates, though the deactivating sulfonyl group limits intramolecular applications.

General amide coupling protocol (illustrative):

1. Charge anhydrous DCM (10 vol) to a dry flask under N₂.
2. Add the amine nucleophile (1.0 equiv) followed by triethylamine (1.5 equiv) at 0 °C.
3. Add 4-(Methanesulfonyl)benzoyl chloride (1.05 equiv) dropwise as a solution in DCM.
4. Allow to warm to room temperature and stir for 1–4 h; monitor by TLC or HPLC.
5. Quench with saturated aqueous NaHCO₃, separate layers, dry organic phase (MgSO₄), filter, and concentrate.
6. Purify by column chromatography or recrystallization as appropriate.

All operations should be conducted under anhydrous conditions to prevent premature hydrolysis of the acyl chloride.

Quality, Purity, and Analytical Verification

Aladdin Scientific supplies 4-(Methanesulfonyl)benzoyl chloride (B725791) as a research-grade reagent. Researchers are advised to verify purity and identity upon receipt using standard analytical techniques:

• HPLC: Reversed-phase HPLC (C18 column, acetonitrile/water gradient) is suitable for purity assessment. A single major peak is expected for high-purity material.
• NMR Spectroscopy: ¹H NMR (400 MHz, CDCl₃ or DMSO-d₆) should show the characteristic aromatic proton signals of a para-disubstituted benzene ring (two doublets, AA'BB' pattern) and a singlet for the methanesulfonyl methyl group (–SO₂CH₃, δ ~3.1 ppm). No acyl chloride proton is observed; purity can be inferred from integration ratios.
• IR Spectroscopy: A strong carbonyl (C=O) stretching absorption near 1770–1800 cm^-1 is characteristic of acyl chlorides; sulfonyl S=O stretches appear near 1300 and 1150 cm^-1.
• Titration: Active chloride content can be quantified by standard argentometric or potentiometric titration methods after controlled hydrolysis.

Store certificates of analysis (CoA) for each lot received. If analytical data do not meet experimental requirements, contact Aladdin Scientific technical support prior to use.