5-Chlorothiophene-2-sulfonyl chloride arrives in chemical plants as a pale, sometimes off-white solid with a pungent edge to its scent that signals its chlorinated nature right from the container. Its unmistakable chemical handle—C4H2ClO2S2—points to a structure built around the thiophene ring, where a chlorine atom sits at position 5 and the forceful sulfonyl chloride group attaches at position 2. That arrangement gives it strength as a sulfonation agent and keeps it in regular rotation for synthesis work across drug and specialty chemical production. In practice, the compound most often reveals itself as a crystalline powder, though labs and factories can sometimes see it pressed into flakes or melted just above room temperature into a faintly yellowish, oily liquid. The distinct shape and scent of a container full of this material always remind chemical workers to glove up and double-check their ventilation.
Under a microscope, the structure breaks down into a five-membered thiophene ring with chlorine hugging the carbon at one end and the sulfonyl chloride bursting out at the other. The molecule rests on a backbone rich in electron density, which makes the sulfonyl chloride moiety highly reactive in the presence of nucleophilic partners. This reactivity explains the broad use in coupling reactions that build sulfonamides, sulfonate esters, and more—a backbone for innovation in pharmaceutical research. It holds a molecular formula of C4H2ClO2S2 and tips the scales with a molecular weight near 197.1 g/mol, which helps production chemists to dose it accurately in process systems. A CAS Number keeps record straight for regulators and handlers, ensuring that workers and supervisors know exactly which chemical sits in the shipping barrel.
Off the bench and out of the drum, 5-chlorothiophene-2-sulfonyl chloride wears several hats. Usually, it appears as a crystalline solid with a sharp melting point that rounds off just over room temperature—often sitting in the 60-65 °C range. If left in an environment above that line, it shifts to a clear or pale yellow liquid with the same reactive nature as its solid counterpart. Density for the solid form tends to center around 1.6 g/cm³, which assists in safe weighing and dosage, especially when guiding powdered material through batch hoppers or onto scales. In the lab, it dissolves efficiently in organic solvents like dichloromethane or tetrahydrofuran but resists the pull of water, where it breaks down and can release choking clouds of hydrogen chloride and sulfur dioxide.
Inside industries from pharmaceuticals to agrochemicals, chemists rely on 5-chlorothiophene-2-sulfonyl chloride as a stepping stone in building blocks that drive the next wave of antibiotics and crop protectants. The raw material gives companies a rare bridge between sulfur-based chemistry and the broader toolkit of halogenation and sulfonation science. Those making custom intermediates seek out this reagent for coupling reactions—noting how the reactive sulfonyl chloride turns it from basic feedstock to functional group transfer agent with a sharp turn of the pipette. Its role as a raw material links upstream refineries and downstream formulators in a supply chain that makes modern chemistry tick.
Anyone who has cracked open a drum of 5-chlorothiophene-2-sulfonyl chloride understands that it demands respect. The release of corrosive hydrogen chloride gas on exposure to humidity means poor ventilation or careless spills can bring on fast irritation for skin, eyes, and lungs. Chemical burns stand among the direct harms from accidental skin contact, with rapid response protocol—safety showers, high-flow eye washes—becoming routine in any facility housing this product. Proper storage keeps containers tightly sealed, set away from heat and protected from any water incursion, often inside dedicated, vented, corrosive storage cabinets. Workers stay aware of reactivity around amines, alcohols, strong bases, and moisture. Regulatory sheets tag the hazardous classification and mark up PPE requirements, while experienced handlers treat every transfer or weighing as a high-stakes operation.
On a trade or shipping manifest, 5-chlorothiophene-2-sulfonyl chloride ships under a specific HS Code—often 2934999090 in regions using the Harmonized System for organic chemicals. Bulk shipments deliver the material in powder, flake, or crystalline solid form, with a minimum assay typically at or above 98%. Buyers track trace-level impurities, water content below 0.5%, and consistent particle size to keep downstream reactions on spec and on time. Technical data sheets list pH, solubility in common industrial solvents, and shelf-life stability at various storage temperatures. All these numbers help purchasing and regulatory teams keep supply compliant, while lab chemists and plant operators use the same figures to protect quality in each run.
A plant manager who has lived through a mid-batch reaction quench knows the difference between a well-characterized sulfonyl chloride and a wild-card intermediate. Consistent physical properties—solid or liquid at process temperature, defined melting point, exact assay—cut down rework and lost yield. Safety depends on understanding how the chloro group and sulfonyl chloride will behave under load, whether charging a reactor or blending for scale-up. As chemicals like 5-chlorothiophene-2-sulfonyl chloride move through the global supply chain, traceability via CAS Number, HS Code, and clear COA documentation builds trust in every handshake from broker to technician. Living with the realities of hazardous materials means error becomes costly quickly; robust hazard statements, gloves, goggles, fume hoods, and containment change an uncertain job into routine, safe work, keeping skilled hands in the industry year after year.
