2-Thienylacetyl chloride stands as an organosulfur compound drawing attention in labs and industry for its specific functional group. It merges the aromatic thienyl ring — a five-membered ring including sulfur — with the reactive acetyl chloride moiety. In its basic form, this chemical appears as a pale-yellow to brownish liquid under standard conditions, giving off a pungent, sometimes acrid, odor familiar to chemists who work with acid chlorides. With its reactivity, the compound functions as a building block for synthesizing pharmaceuticals, agrochemicals, and various organic synthesis intermediates. Handling the neat material leaves no room for error, as you’ll notice the fumes start to irritate mucous membranes if proper care isn’t taken.
Chemically, 2-Thienylacetyl chloride carries the formula C6H5ClOS, reflecting one chlorine, one oxygen, and one sulfur within its molecular framework. Its molecular weight measures approximately 176.63 g/mol. In a bottle, you notice dense, oily fluidity at room temperature, though it can show some degree of crystallization under cooler storage. The density hovers around 1.26 g/cm³ at 25°C, higher than many common organic solvents, so it weighs solidly in the hand. The structure features the thienyl ring (a sulfur-embedded aromatic ring reminiscent of benzene’s stability but with more reactivity) bound via a -CH2- bridge to the acetyl chloride group. Examining a sample under good lighting, the clear or slightly amber liquid highlights its purity, but older batches or those exposed to air might develop minor solid impurities.
2-Thienylacetyl chloride appears as a liquid under standard conditions; some suppliers manage to offer it in stabilized or solution forms for specialized needs, since its fumes can be corrosive and it hydrolyzes in moist air. In commercial labs, chemists sometimes pour carefully from bottles where you may see droplets escaping as they transfer quantities from liter or smaller stock solutions. In terms of macroscopic appearance, you’re not likely to see a solid or powder form unless it’s an impurity or a crystallized breakdown product after exposure to low temperatures or moisture. In handling raw materials quality, purity often exceeds 98%, as trace impurities complicate downstream reactions. For industrial-scale synthesis, specs might detail chloride content, water content (it must stay low, often below 0.2%), and appearance (colorless to pale yellow, no solids). The HS Code for 2-Thienylacetyl chloride, under chemical trade regulations, falls into the 2916 category — acid chlorides and related derivatives — reflecting its global track for import and export oversight.
On the molecular front, the relatively high density hints at the compact atomic arrangement and the weight contributed by the sulfur atom compared to purely hydrocarbon-based acid chlorides. Volatility mirrors other low-molecular-weight acid chlorides, where the liquid gives off fumes that react quickly with moisture, making immediate work under a fume hood necessary. Colleagues handling the chemical remark on its tendency to fog up glassware with HCl vapor if cap threads aren’t tight, or if a bottle sits open longer than necessary. Practical scenarios in the bench-scale lab often dictate working fast — measure, pour, reseal. Splashes may cause localized burns; the effects are immediate with persistent irritation on contact with skin or eyes. If spilled, the viscous liquid spreads rapidly and a sharp odor develops as it reacts with atmospheric moisture, producing hydrochloric acid and residual thienylacetic acid.
The safety profile for 2-Thienylacetyl chloride demands respect. Classified as a hazardous and harmful material, its reactivity places it in stringent storage and transport categories. It can cause severe burns upon contact and serious damage to respiratory passages if inhaled. Even a quick dash of the liquid on glove or glassware leaves an acrid signature you recognize after some experience. Anyone working with this compound wears chemical-resistant nitrile or butyl gloves, splash-proof goggles, and relies on local ventilation — ideally a certified chemical fume hood. Chemical burns are the key risk — evidence from safety reports and poison control data suggest acid chlorides in general, including this compound, rank high for accidental injury in both educational and manufacturing sites. Regulation in most jurisdictions includes storage under dry nitrogen, clear hazard labeling, secondary containment for bottles (especially in liter quantities), and strict tracking of material quantities.
Experienced synthetic chemists know this compound serves as a prized raw material — the reactivity of the acid chloride group opens doors for quick attachment to amines, alcohols, and phenols. Its thienyl backbone brings unique properties to molecules in drug discovery and advanced polymer science. Across process chemistry, the ability to transfer the 2-thienylacetyl group efficiently onto other substrates is critical in assembling pharmaceutical intermediates, certain dyes, agricultural agents, and specialty materials. When working in a process or research setting, controlling the moisture environment and metering the compound slowly helps prevent side reactions, preserving not only safety but product yield. Waste handling gets extra attention too — neutralization with aqueous base produces copious heat and fumes. Skilled staff always wear respirators, especially if handling more than small reaction scales.
Looking at ongoing concerns and the real-world risks, improvements in packaging and transport remain front and center. Designers introduce more robust, break-resistant bottles with positive-seal caps and venting systems for pressure build-up, reducing accidental exposure. Remote-controlled or glovebox-supported operations can further reduce human contact, especially as automation expands in chemical manufacturing. Specialized training sessions — both in-person and online — boost operator awareness far more effectively than one-off safety briefings. Emerging alternatives and green chemistry initiatives still grapple with replacing acid chlorides in many key applications, given their efficiency. Process innovation focuses on limiting scale and improving containment. In research environments, teams pay special attention to spill kits appropriate for acid chlorides, with calcium carbonate instead of standard absorbents, as the latter may not neutralize corrosives fast enough. Over time, investments in air monitoring and maintenance of quality safety equipment has proven the best route to prevent injury, loss of product, and regulatory headaches.
