From early benzo[b]thiophene studies to modern-day synthetic tweaks, people have been curious about how halogen substituents influence chemistry. In the postwar era, organobromine chemistry gained real traction, and 4-bromobenzo[b]thiophene stuck out for both its versatile backbone and the unique reactivity of the bromo group in position four. Synthetic chemists hunted for ways to modify thiophene rings, and as analytical techniques sharpened and chromatography took off, separating and purifying these aromatic heterocycles became second nature in research labs. Labs at major universities in Europe and the US reported reliable routes to this molecule in the seventies. From there, the compound made its way into catalogs, often as an intermediate for more complex drug targets and advanced material prototypes. The journey mirrored organic chemistry’s embrace of sulfur-based small molecules, driven not by a single discovery but by a steady stream of technical advances and the persistent hunt for new building blocks.
4-Bromobenzo[b]thiophene is a specialty aromatic compound where a bromine atom attaches to the four position of a condensed thiophene ring system. It typically lands in the hands of chemical researchers, material scientists, and those in pharma who see value in tunable, aromatic heterocycles. Its structure gives it edge: the sulfur adds flexibility for ring-based modifications, while bromine’s presence opens up cross-coupling pathways. Most suppliers provide it as a crystalline solid, known for its stability compared to more volatile halides, which means it ships well and holds up under basic storage. You often see it in neatly labeled glass containers in the fridges of research labs, a crucial, if humble, starting point for countless synthetic journeys.
On the bench, 4-bromobenzo[b]thiophene clocks in as a light, off-white crystalline powder, neither sticky nor powdery enough to raise handling concerns. Its molecular weight hovers around 227 g/mol. The melting point often sits above 60 degrees Celsius, though purity and crystalline form can push it higher or lower. Aromaticity makes it less reactive than plain alkenes, yet not as stubborn as polycyclic aromatics. The bromine group lends density and can slightly boost the compound’s lipophilicity, a property that catches the eye of medicinal chemists. It’s soluble in most polar organic solvents, not so much in water, echoing the usual story for aromatic halides. Scent-wise, it doesn’t punch out offensive notes, but it pays to store it airtight; humidity rarely causes trouble, but long-term exposure could promote slow hydrolysis or discoloration.
Suppliers list purity, usually above 98% for research grade. Labels spell out CAS number (19725-71-2), molecular formula (C8H5BrS), lot numbers, and manufacture dates. Batch traceability is non-negotiable for regulated projects. Some vendors provide spectral data: NMR, MS, and occasionally IR, confirming structure and ensuring nothing slips in from side reactions. Every package should give hazard statements, UN codes when needed, and clear handling tips. Even small-scale researchers rely on this chain of information to ensure their data stands up to scrutiny. Mislabeling can derail months of effort, so every ampule or vial usually wears a tamper-evident seal out of respect for chemistry’s exacting standards.
Over the decades, chemists have used electrophilic bromination of benzo[b]thiophene to get the four-position selectivity. The classic approach uses N-bromosuccinimide (NBS) as the brominating agent with a touch of light or radical initiator. Some lean on elemental bromine, but this brings more safety headaches and lower selectivity. NBS, with its controlled delivery and mild reaction scope, gives solid yields and a cleaner product after quick column chromatography. Those with industrial ambitions might opt for flow chemistry or tweak solvents to scale up, but the kitchen chemistry—stirring flasks in fume hoods and watching color changes—still rules most labs. Recrystallization from solvents like ethanol or acetone sharpens up the product, ridding it of side products common in heterocyclic syntheses.
4-Bromobenzo[b]thiophene is a darling for those who love cross-coupling chemistry. The aromatic bromine gets swapped out in Suzuki or Sonogashira reactions, tacking on complex aryl, alkynyl, or vinyl bits with help from palladium catalysis. In my hands, running a Suzuki coupling on this scaffold usually gives consistently high conversions with boronic acids, provided you pamper it with right ligands and bases. You can also direct-lithiate the position next to the sulfur—using something punchy like n-butyllithium—if you want to drive further functionalization. Nucleophilic aromatic substitution isn’t out of reach, though conditions often skew harsh. Such versatility pulls in chemists chasing new ligands, electronic materials, or complex natural product analogues.
Depending on the context, suppliers or publications might call it 4-bromo-benzo[b]thiophene, 4-bromothionaphthene, or 4-bromo-1-benzothiophene. The CAS number 19725-71-2 usually keeps everyone on the same page. In catalogs, you’ll see both IUPAC and common names interchanged, proving there’s more than one way to signal a molecule’s identity. Whether in patents, supplier sheets, or lab notebooks, these names serve as a universal handshake between chemists around the world.
Working with 4-bromobenzo[b]thiophene doesn’t rank as especially hazardous, but attention to basics pays off. Brominated aromatics can irritate skin and eyes, and organic dusts—no matter how benign they look—pose inhalation risks. Gloves, goggles, and lab coats become second nature. Fume hoods aren’t just a box to contain smells; they protect from airborne particles and reduce exposure to volatile side-reactions. SDS sheets flag acute toxicity and environmental concerns, warning that disposal can’t be casual. My own experience underscores the value of keeping accurate logs on handling and storage. Spills don’t often cause chaos, but keeping the workspace clean cuts down on unnecessary exposures and maintains the integrity of subsequent experiments. Most institutions mandate training in handling halogenated organics as much for environmental reasons as for individual safety.
In the lab, 4-bromobenzo[b]thiophene earns respect for its ability to bridge medicine, materials, and method development. Medicinal chemists scout it as a precursor for antitumor and antiviral lead compounds, leveraging that sulfur ring as a hydrogen-bonding partner or a mimic of biological motifs. Material scientists tailor it into organic semiconductors, dyes, and light-absorbing molecules for solar energy. Its compatibility with metal-catalyzed reactions opens up whole libraries of derivatives—each potentially a candidate for new sensors, polymers, or small-molecule drugs. Academic groups value it for proof-of-concept syntheses, testing out new catalytic cycles and reaction conditions before scaling up. The recurring presence in research pipelines underlines its role as more than a one-trick pony; it provides a flexible foundation for scientific exploration.
R&D runs on the back of reliable building blocks, and 4-bromobenzo[b]thiophene rarely lets down those shaping tomorrow’s chemistry. Recent literature shows it woven into next-generation organic electronics—OLEDs and field-effect transistors—with modifications tuning charge mobility and light output. In pharma workflows, new antineoplastic and CNS-active molecules start with cross-coupling at the bromo site, optimizing for both activity and metabolic stability. Collaboration between academia and industry often pushes for greener, scalable syntheses to stretch budgets and stay on the right side of regulations. Having worked with dozens of halogenated heterocycles, I’ve seen first-hand how small changes to a molecule’s softer spots—the bromine, the heteroatom—can open up surprising new directions. As analytical tools improve, so does the ability to characterize byproducts and chase down elusive intermediates, driving faster, smarter optimization.
While not flagged as highly toxic, 4-bromobenzo[b]thiophene still demands respect for its possible health and environmental impact. Acute exposure may irritate mucous membranes; chronic exposure data remains limited. Most toxicity profiles come from studies on related brominatedthienylarenes, which suggest low acute oral toxicity but flag longer-term exposure as an open question. Waste handling rules prevent simple dumping, keeping runoff out of waterways known to suffer from persistent organic pollutants. Environmental fate studies indicate the molecule’s aromatic core resists quick breakdown, raising questions about bioaccumulation that regulatory bodies increasingly press suppliers to address. In my experience, safe practice begins with the assumption that data gaps hide not safety, but risk—and until more thorough studies come in, precaution outpaces convenience in chemical safety.
The outlook for 4-bromobenzo[b]thiophene glows brightest in the hands of innovators hungry for adaptable scaffolds. Material designers predict more use in flexible electronics and smart coatings as the hunger for unique heteroaromatics grows. Pharma hasn’t hit the end of the road either. As drug discovery noses deeper into underexplored chemical space, the marriage of sulfur and halogen chemistry in this core structure invites fresh campaigns against diseases still lacking good treatments. Greener, more efficient syntheses now edge onto the R&D agenda, as industry eyes performance hand-in-hand with sustainability. Having handled dozens of aromatic intermediates myself, I see clear signals: so long as research keeps pressing for new reactivities and smarter modifications, this molecule will keep earning its shelf space—and maybe a bigger role in shaping technologies a decade from now.
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