3-Iodothiophene brings together the strength of halogen chemistry with the unique backbone of thiophene. Its formula, C4H3IS, consists of four carbons, three hydrogens, one iodine, and one sulfur. The thiophene ring, aromatic and five-membered, forms the core, while iodine attaches at the third position. The addition of a heavy halogen atom impacts molecular weight, which comes out to about 209.04 g/mol, and alters some reactivity compared to plain thiophene. Having handled many halogenated aromatics in the lab, I’ve seen how that iodine atom doesn’t just change the structure — it reshapes the way this compound behaves whenever it meets reagents for cross-coupling or synthesis. The sulfur atom in the ring brings additional reactivity and sometimes a faintly sharp odor that hints at its chemical personality.
This chemical can appear as small flakes, crystalline powder, off-white pearls, and in some batches, as solid crystals. I’ve opened jars finding everything from loose, powdery material to larger, glistening plates, especially when it’s stored carefully and protected from moisture. Its melting point hovers around 25 to 30°C, so at room temperature, it can be a solid or a slightly oily liquid — storage conditions tip the scale. Density clocks in around 2.1 g/cm³, which surprises those expecting a lighter aromatic — iodine adds weight. As a raw material, it dissolves in polar organic solvents like acetone, DMF, and chloroform without much trouble, supporting its use in liquid-phase reactions. Its mild, sometimes pungent scent brings back vivid memories of afternoons spent working with sulfur and halogen compounds, the whiff unmistakable for those familiar with heteroaromatic chemistry.
Industrial buyers often look for high purity, usually above 98%, which supports clean products in downstream pharmaceuticals, agrochemicals, and advanced material synthesis. The purity standard matters — contaminants interfere with reaction yields and reliability, which echoes my experience running cross-coupling reactions that respond poorly to dirty starting materials. Laboratories sometimes keep 3-iodothiophene stocks in amber vials, shielded from light, since extended UV exposure breaks it down faster than some might expect. Looking at the HS Code — 29341000, typically used for heterocyclic compounds containing a thiophene ring — trade and shipping are tracked under this category, making customs paperwork smoother for importers and exporters.
Handling 3-iodothiophene, like many halogenated aromatics, means keeping an eye on protective gear. I've worked with this material under a fume hood, gloves on, since it carries hazards. Its vapors and dust can irritate the lungs, skin, or eyes, and in some cases, extended exposure can harm thyroid function due to the iodine content. Its flash point remains relatively low, so open flames and sparks stay far away. Spilled powder tends to cling and requires careful grid cleanup. Safety data sheets underline the risk of hazardous decomposition products — including toxic gases — during heating or fire, and small-scale users need to label containers clearly to avoid costly mistakes.
Many of the difficulties with 3-iodothiophene come from sourcing and storage. Supply chain interruptions lead to higher prices, largely because iodine content relies on global raw materials. I remember price spikes during years when mining or export of iodine fell. Laboratories hoping for greener chemistry practices see the production and disposal of halogenated waste as issues. Stocking this compound in dry, dark, and cool places prolongs its shelf life, but even then, small leaks or vapor losses require periodic checks. Solutions involve tracking batches, using secondary containment for bottles, and coordinating closely with suppliers for stable delivery. R&D teams that push for safer synthesis routes or better recovery and recycling of waste promise longer-term answers. Finding alternatives for certain cross-coupling reactions or phase-transfer applications may gradually reduce dependence on iodine-based intermediates, though for now, 3-iodothiophene stays crucial for many chemical industries craving precision and reactivity.
