Back in the mid-20th century, folks in the chemical labs started looking for ways to add sulfur atoms into aromatic compounds. That’s where 2-thienylacetic acid found its groove. Research cropped up across Europe and North America, with chemists chasing new flavors of heterocyclic acetic acids for reaction studies and early drug leads. While the compound never got the crowd-pleasing buzz of bigger names like salicylic acid, a handful of researchers kept hammering out papers on 2-thienylacetic acid all through the 1960s and 1970s. Library shelves and digital archives still have those yellowed journal pages, a testament to dogged curiosity. Today’s organic labs pull it off the shelf for building blocks or as a benchmark for tweaking reaction methods, but those early pioneers laid the groundwork. Experience in research labs tells me you don’t need a blockbuster molecule to make useful chemistry.
2-Thienylacetic acid has a down-to-earth profile but a stubborn utility. With its thiophene core and a simple acetic tail, it offers a reliable starting point for making all sorts of sulfur-containing compounds. Chemists spot its use both in academic work and small-batch manufacturing. Bulk sales rarely match the volumes of common industrial acids, yet the right buyers keep it moving for reactions where a sulfur heterocycle makes all the difference. The chemical usually shows up as an off-white powder, sometimes a bit tan, depending on how carefully the manufacturer watches the process.
Pull that cap off a 2-thienylacetic acid tub and you’ll see fine, crystalline granules or a fluffy powder. Its molecular formula is C6H6O2S, with a molar mass around 142.18 g/mol. Once you get it out of the bottle, a faint, slightly sharp odor sometimes creeps up – not overwhelming, just a whisper of its sulfur atom. Laboratory thermometers clock its melting point between 74°C and 78°C, and the substance stays put at room temperature. Slide it into water and you’ll find modest solubility, a bit better in ethanol, dioxane, or ether. The acid character shows through with a pKa around 3.62, lining up with its mildly sour punch in solution.
Chemical supply houses stick labels on the bottles marking 2-thienylacetic acid with purity usually above 98%. You’ll spot the batch number, production date, molecular structure, and hazard codes – mainly skin and eye irritant warnings. For those keeping close records, common identifiers include CAS number 1918-77-0 and EC number 217-648-0. Labels also carry the UN transport number if the shipment crisscrosses borders or rides freight trucks. Laboratories pay heed to those details, as mislabeling sets everyone up for mistakes down the line. Most suppliers include a certificate of analysis to keep quality claims honest.
Synthesizing 2-thienylacetic acid involves a few reliable tricks. The most familiar approach walks through a Friedel-Crafts acylation, where thiophene reacts with chloroacetic acid under the firm hand of aluminum chloride or another Lewis acid. The reaction’s exotherm needs a careful touch since overheating brings side products and headaches. A cleaner alternative sometimes uses sodium thiophenolate and bromoacetic acid, letting nucleophilic substitution do the heavy lifting. Once the reaction wraps, there’s plenty of washing, filtration, and recrystallization before the pure acid comes out the other end. Scale-up means beefier glassware and stricter temperature control. Listening to old colleagues swap stories, it's clear that the winner in this game is always the technician paying close attention.
Once in hand, 2-thienylacetic acid opens the door to dozens of reactions. Common transformations include esterification with alcohols, amidation with amines, and coupling to form more elaborate heterocycles. The acetic acid side reacts in ways familiar from benzylic chemistry, but the thiophene moiety pitches in unique reactivity at the 2-position. For instance, halogenation there leads to halothiophenes with solid pharmaceutical value. Researchers sometimes oxidize it further to tweak biological activity or to anchor the compound into more complex architectures. In the hands of creative chemists, this little acid helps ring in all manner of chemical change.
In catalogues and research papers, names get swapped around. Spend a day poking through the literature and you’ll spot “2-thiophenylacetic acid,” “2-thienyl ethanoic acid,” or, written without spaces, “2thienylaceticacid.” A few suppliers simply call it “thiophene-2-acetic acid.” PubChem, ChemSpider, and other databases keep all those hats straight, which keeps researchers from accidentally ordering the wrong bottle. Though synonymous, these names point back to the same molecule and make searching a bit of a chore unless you know the landscape.
Working with 2-thienylacetic acid doesn’t require a hazmat suit, but it still needs respect. It can cause some eye and skin irritation, which means gloves and goggles stay on until everything’s cleaned up. Inhalation—or worse, ingesting it by accident—brings on mild nausea or irritation. Good ventilation rules the day, along with local exhaust hoods in busy organic labs. Disposal usually lands it in the aqueous organic waste stream, following well-worn environmental regulations. For storage, tight lids and cool, dry shelves keep the product solid and pure. Regulatory bodies like OSHA in the US and REACH in Europe have compliance frameworks, but 2-thienylacetic acid doesn’t trigger the toughest rules unless someone goes wild with amounts.
Pharmaceutical development leans on compounds like 2-thienylacetic acid to tinker with new drug backbones. Researchers exploring antiseizure drugs, anti-inflammatory candidates, and certain antibiotics have built on its framework. Agrochemical companies scout it for herbicide and fungicide leads, using the combination of sulfur and aromaticity to mess with plant biochemistry. Analytical labs sometimes use the acid as a reference for chromatographic calibrations or to build up training samples for GC-MS and HPLC runs. In material science, its derivatives play a role in polymers featuring thiophene units, with electrical or optoelectronic properties inching into solar or LED components.
For years, scientists kept poking at the thienylacetic scaffold for all sorts of research reasons. Some looked for new antibiotics, others pressed for cancer leads in the test tube. Folks in green chemistry try tweaking the preparation routes, shaving off waste and energy. R&D teams twisted the compound’s arms to build new ligands, surfactants, or ionic liquids. A few groups dove into the synthesis of photoactive compounds by linking the acid with electron-rich moieties. From my own bench days, seeing thienylacetic acid in the inventory always meant curiosity was about to meet glassware and pipettes.
The toxicity profile gets attention because adding sulfur often rings alarm bells. Data shows 2-thienylacetic acid doesn’t pack a dangerous wallop at the scale most labs use. Animal studies show only moderate acute toxicity, mostly hitting the digestive tract or causing mild irritation on contact. Toxicologists keep a healthy skepticism, so longer-term, high-dose studies run in parallel for any drug candidates build off the structure. In environmental testing, the acid breaks down reasonably fast, but spills into waterways need cleanup to avoid harm to aquatic life. My own reading finds few reports of chronic harm – just a need for good lab sense and solid personal protective gear.
Those who keep eyes on new technology spot the sulfur-rich thiophene ring showing up in modern applications, especially organic electronics. 2-Thienylacetic acid feeds into research around flexible solar cells, new photoconductors, and improved field-effect transistors. In pharmaceuticals, folks still see room for growth using the structure to chase central nervous system drugs or antimicrobial leads with fresh resistance profiles. Lab-scale synthesis keeps getting greener, with milder reagents and lower waste targets, which might tip large batch production from niche to mainstream. After decades spent as a workhorse for specialized projects, thienylacetic acid stands steady for anyone looking to build new molecules, tackle practical problems, or just keep learning about what sulfur can really do.
