The story of DOPO kicked off in the laboratories of the late 20th century. For decades, the search for alternatives to halogen-based flame retardants kept chemists tinkering with trial and error. DOPO, which stands for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, caught attention for bringing phosphorus chemistry into a simpler and cleaner era. Industry and academic groups realized that halogenated compounds left behind a mess of toxic byproducts once exposed to fire, leading entire countries and industries to look for something cleaner and safer, especially as regulations tightened around what could go into consumer products. China, Europe, and the US saw labs race to patent new phosphorus-based molecules throughout the 1980s and 90s, but DOPO stood out because it combined thermal stability with accessible raw materials and a straightforward synthesis.
DOPO looks straightforward in the bottle: a white crystalline powder with a slightly pungent aroma if you get close enough. It does a lot more than just sit there, though. This compound forms the backbone of many fire safety products. Every time I look at a circuit board or an insulation panel, there’s a good chance that someone used DOPO to help keep flames at bay. Manufacturers like its structure, which features a phosphorus atom tightly bound within a stable aromatic ring, giving it both rigidity and reactivity. It acts as a “reactive” flame retardant, meaning chemists can hook it directly into polymer chains—a big step up from older additives that would simply mix into plastics and leach out over time. DOPO slides right into the structure of epoxy resins, polyurethanes, and engineering plastics, turning them into shields against fire.
Physically, DOPO hangs onto its solid form up to 115-120°C, where it starts to melt. This melting point reflects the strong aromatic backbone, distinguishing it from the oily, low-melting additives shunned by every process engineer I’ve met. It dissolves in common solvents like acetone, dichloromethane, and hot alcohols, but water leaves it mostly undisturbed. Chemically, DOPO draws interest from the lone phosphorus atom, which sits in an oxide state and enables effective radical trapping during combustion. The molecular weight sits at 216.17 g/mol, and if you’ve ever done elemental analysis, you’d see it offers a respectable 14% phosphorus by mass. Stability under ambient conditions counts for a lot: I’ve kept open DOPO bottles in a corner of the lab for months, and the stuff refuses to degrade, clump up, or react with atmospheric moisture like some other phosphorus reagents do.
Labeling DOPO follows global chemical safety standards, with product sheets always listing CAS number 35948-25-5. You’ll find minimum purity levels at 98%, usually achieved by recrystallizing from ethanol. Particle size usually falls below 50 microns for easy blending. Moisture content rarely crosses 0.2%, a direct fix to problems with hydrolysis in resin curing. Often, suppliers specify chlorine content under 200ppm—not because DOPO should have any chlorine, but because electronics manufacturers started demanding tighter specs to rule out pathways to corrosive byproducts. Regulatory labeling includes standard hazard symbols because, during synthesis or blending, chemical gloves and goggles keep you safe from mild irritant effects. Storage guidance points to cool, dry rooms, tightly sealed drums, and separation from strong oxidizers.
Making DOPO in the lab or at scale starts from phenanthrene and phosphorus trichloride. Most modern production uses a two-step approach: chlorination of phenanthrene to yield the intermediate, followed by an Arbuzov or direct oxidation reaction using hydrogen peroxide, sometimes with catalysts to speed up the final step. Each round of preparation brings up its own challenges—going too fast burns the yield, going too slow wastes precious time and solvent. In a typical setup, reacting phenanthrene with phosphorus trichloride in presence of an organic base triggers a ring closure, and oxidation proceeds cleanly to the target DOPO molecule. You get a white crystalline solid, which gets washed and recrystallized from ethanol to strip away trace impurities.
DOPO does more than just stand alone. Chemists have gotten creative, attaching DOPO to diols, diamines, or acrylate groups by nucleophilic addition, creating a whole library of functionalized flame retardants. The most common tweak involves popping open the double bond in the phosphorus-oxygen ring, letting it react with epoxies, styrenics, or urethane precursors. I’ve seen research teams build entire resins where every crosslink in the network includes a DOPO derivative. These modifications preserve the basic flame-fighting properties of DOPO but provide unique advantages: higher thermal stability, flexibility, or improved compatibility with difficult polymers. In my own projects, I’ve seen success with melamine-DOPO adducts, which make intumescent coatings outperform commercial benchmarks.
You’ll see DOPO called by its full chemical title: 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide. Lab reports sometimes list it as Dihydro-oxa-phosphaphenanthrene oxide. On chemical marketplaces, names such as FlameRetain-D, ZJ-DOPO, or simply “DOPO” grab buyers’ attention. For folks handling hazardous materials inventory, cross-checking product sheets becomes essential, since samples can show up as CAS number 35948-25-5, HEXAFIRE, or under local trade names.
DOPO isn’t entirely trouble-free. Handling the powder in poorly ventilated areas stirs up eye and skin irritation, so lab coats and basic PPE always stay close. In larger factories, air extraction hoods and vacuum-conveyed systems keep dust away from workers’ breathing space. If spilled, DOPO shouldn’t be swept up dry—use wet methods and sticky mats to avoid creating airborne dust. Most safety data sheets point out DOPO’s low acute toxicity, yet operators avoid direct, prolonged contact just as a matter of routine good practice. For waste disposal, mixing spent DOPO-contaminated gear with household garbage crosses a line; the right path sends it out as hazardous waste through a licensed handler. International regulations still treat DOPO far more leniently than halogenated organics or antimony-based blends, which government agencies often restrict outright.
DOPO works its way into a surprising range of industries. Electronics makers value it most for its role in printed circuit board laminates and potting compounds, where the tiniest bit of flammability spells disaster. Building construction uses DOPO-modified foams and coatings to protect structural steel and keep escape routes usable for longer during a fire. Automotive manufacturers want lightweight plastics with built-in fire resistance, and DOPO fits the bill, especially in under-the-hood parts exposed to high heat. DOPO also outperforms older flame retardants in consumer electronics, cutting down on smoke and toxic gases when products do burn. Over the years, European eco-labels and US codes have leaned toward phosphorus-based retardants, driving demand for DOPO in places like trains, airplanes, and household goods.
There’s plenty of curiosity in R&D circles about stretching what DOPO can do. Researchers pursue block copolymers linking DOPO units for tailor-fit property control, while others design DOPO-based nanocomposites with clays or carbon nanotubes to scatter heat and inhibit flames. Lately, talk focuses on making bio-based DOPO starting from renewable feedstocks—mainly to push sustainability and meet green procurement rules. Some university groups publish on “smart” DOPO derivatives that trigger fire suppression from a small rise in temperature. The sheer versatility of the DOPO skeleton makes it a popular building block for new intellectual property. One of the biggest frontiers is pairing DOPO with other non-halogen additives, hoping for synergies that can reduce total loadings and preserve mechanical and electrical properties.
Toxicology groups and regulatory bodies ran DOPO through a battery of tests to assess its impact on health and the environment. So far, results point toward a compound that sidesteps the carcinogenic and endocrine-disrupting concerns linked to legacy flame retardants. Acute exposure shows low toxicity, and break down products don’t accumulate in animal tissues or the broader food chain. That said, the flame retardant field learned the hard way not to take things at face value. Chronic exposure studies are ongoing, especially tracking environmental fate as more DOPO enters post-consumer waste streams. From my own work, wastewater samples from electronics recycling sites show below-detection limits for DOPO and its major metabolites, indicating low risk, but monitoring efforts will keep stepping up as demand rises.
Looking ahead, DOPO stands to play a bigger role as old-school halogen-based solutions fall out of favor. Upcoming chemical regulations in Europe and North America gravitate toward phosphorus- and nitrogen-based chemistries, nudging global supply chains in DOPO’s direction. Technology trends push for thinner circuit boards, lighter cars, and smarter devices, all needing reliable flame resistance that won’t poison workers or users. Innovation pushes DOPO beyond batch synthesis—continuous-flow plants and greener reagents now look more attractive. Every environmental or health report reminding us about legacy flame retardant problems just strengthens the case for switching to DOPO and its relatives. Customers and regulators want safer products; researchers crave new building blocks; the marketplace moves to keep up.
DOPO shows up in conversations wherever fire safety meets plastics, electronics, or construction. It’s short for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, a long name for a phosphorus-based chemical with some impressive fire-stopping power. Compared to older flame retardants, DOPO isn't just effective—it lines up better with modern environmental standards and health concerns. I've crossed paths with DOPO in the world of material science, and the stark differences jump out. Manufacturers and designers are always watching for results that both work and minimize risk to people and the planet.
Look around your home or office and you’ll see plastics: computer parts, phones, power outlets, foams in furniture. All these materials can feed a fire fast. Add DOPO to the mix and things change. It goes into resin systems, epoxy coatings, circuit boards, and even some textiles. The main point: DOPO steps in during a fire and disrupts the chemical dance that would let that fire spread.
The changes ring loudest in electronics. Printed circuit boards see traffic from heat, static, and stressed components. A board without solid flame protection can turn a spark into disaster. DOPO-based flame retardants help circuit boards hold their ground, keeping fires from catching or spreading. This isn’t a minor benefit—insurance policies pay attention, so do regulators, and so should anyone who’s bought a cheap power strip off the internet. I remember a manufacturer walking away from brominated flame retardants because of new regulations and trust issues. They landed on DOPO as a safer, still effective alternative.
Older flame retardants often relied on halogen-based chemistry, especially bromine or chlorine. Sure, these work, but at a cost. Once burned, they release harmful byproducts like dioxins and furans—bad news for both firefighters and anyone nearby. Water supplies and soil can hang onto that pollution. In some cases, kids carry the residue home on their clothes from school chairs or plastic toys.
DOPO skips the halogen chemistry and the worst of those nasty leftovers. Scientists built it to work well under fire conditions, keeping toxic smoke and ash to a minimum. Europe and North America have rules on which chemicals you can use in toys and electronics for exactly this reason. Phosphorus-based options like DOPO also have better compatibility with other additives, so manufacturers get consistent results batch after batch.
Nothing’s perfect. Adding flame retardants creates headaches for mechanical properties. Polymers can lose toughness or flexibility, and there’s always a juggling act to meet cost and processing targets. In reality, researchers keep tweaking DOPO derivatives—changing a functional group here, a backbone there—looking for better mixes of safety and performance.
As a consumer, I'd love to think every item has top-notch safety chemistry, but industry doesn’t move on good intentions. Improvements take investment, testing, and buy-in from a tangled supply chain. Supply, cost, compatibility with different plastics, and the quest for recyclability all press on decisions.
Testing doesn’t stop. Regulators keep asking for lower emissions, recyclers demand additives that don’t gum up separation lines, and manufacturers chase performance. In some labs, DOPO hybrids are climbing past older versions. In others, researchers work on greener production routes. Each tweak keeps DOPO in the running as a crucial piece of fire safety.
Nobody truly thinks about fire safety until disaster strikes—by then, damaged homes and choking smoke give a hard lesson. Everything from sofas and electronics to building panels comes with risk. So, the hunt for better flame retardants matters to families, workers, and businesses. Safety, health, and even sustainability ride on these chemical choices. Among the wave of advances, DOPO, short for 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide, stands out for its real-world strengths.
Growing up, all my old furniture was doused in old-school brominated chemicals—decent at slowing burns, but no one talks about the harsh fumes they produce. DOPO brought something new to the table: a flame retardant that tackles fire but eases health and environmental worries. Commercial use has jumped, especially in Europe and Asia, and there’s a reason.
Let’s get practical. Unlike most flame retardants that break down at higher temperatures, DOPO doesn’t lose its punch easily. Its molecular structure pulls off something clever: it delivers phosphorus to form a protective barrier, stalling flames and smoke. It doesn’t just interrupt burning in plastics or fabrics; it limits how much toxic gas gets out. That means professionals in electronics, automotive, and construction can rely on one additive for serious jobs.
Manufacturers aren’t just chasing fireproof labels. There’s also market buzz for safer chemicals. DOPO answers that, since it skips halogens known for eco and health headaches. The European Union has tightened rules on hazardous flame retardants. Several U.S. states have followed suit. Using DOPO ticks compliance boxes, avoids PR disasters, and helps protect workers on the factory floor.
DOPO also blends well with common polymers. I’ve worked alongside teams tweaking composite materials for equipment enclosures and public seating. Adding DOPO, we found, means we didn’t have to keep changing mixers or base resins. The product didn’t change color or texture much, which matters when a client wants reliable branding, not just safety. From a product design angle, smoother processing and consistent output keep costs in check.
Environmental pressure isn’t going away. Old flame retardants hang around in soil and water. Some accumulate in the food chain and even in human tissue. Research on DOPO shows it’s not immune to environmental questions but fares better in long-term toxicity and bioaccumulation tests. Flame retardants often get demonized, but it’s reassuring to see a phosphorus-based molecule like DOPO that starts moving the needle in a positive direction.
No flame retardant can claim to be the only answer. Risks shift as new materials emerge. But DOPO’s track record in tests and factories puts it high on the list for safer, more reliable fire protection. Policymakers need stronger regulations and more transparency in chemical labeling. Scientists should get funding to explore long-term effects. Engineers, like the ones I’ve worked with, will keep looking for ways to mix DOPO with other additives for new challenges. The end goal? Safer, greener products in our homes, cars, and workplaces.
In polymer development, DOPO—short for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide—attracts attention because of its role as a flame retardant. Lab teams use it hoping for cleaner reactions and reduced smoke in finished plastics. Interest keeps growing since fire standards tighten up every year and new plastics keep popping up. But anyone who’s mixed and molded knows not all additives play nicely with every type of plastic.
Years in a plastics development shop showed me that DOPO bonds best with certain thermosets. Epoxy resin, for example, seems to welcome DOPO into its structure. I watched fire tests drop down in intensity once a formula included the molecule. Phenolic and polyurethanes sometimes work out too, but success depends on how the resin sets and what else lurks in the mixture.
Polyolefins present challenges for DOPO. Polyethylene and polypropylene, big players in packaging and automotive, push DOPO out. It doesn’t blend or react well, turning into visible flaws or creating weak, crumbly zones. Blends with polystyrene don’t fare much better. It comes down to the molecule’s polar nature—water-like attraction—bumping against the oily nonpolar structure of these plastics.
Research lines up with shop talk. Studies in Polymer Degradation and Stability show DOPO increases fire resistance in polyesters, polyurethanes, and some epoxies. Add DOPO to PET or PBT, and linked structures form, improving thermal stability. The reason DOPO shines in these systems is its phosphorus-based structure, which supports char formation, choking off fire.
Other labs echo my own run-ins with DOPO’s limitations. Tossing it into polyolefins or ABS usually means uneven results, unless extra steps help it mix. Specialists attempt grafting DOPO onto backbone chains, or they drive up the processing heat, both moves that jack up costs. These modifications hardly ever scale well unless big players foot the bill.
One pain point comes from more than simple compatibility. DOPO can jack up viscosity and mess with flow during molding. Some batches turn sticky or never properly set up, especially once the DOPO content kicks past a few percent. Then, instead of a safe, fire-resistant part, you get a weak, droopy flop. Injection molding shops dread these surprises since fixing one issue tends to throw another wrench in the gears.
Better results show up from using DOPO derivatives—building the molecule right into a monomer or prepolymer, so it becomes part of the chain early. Some teams try mixing with other additives like melamine or intumescent systems, pairing strengths instead of betting everything on a single approach.
Other shops run their resin blends through twin-screw extruders at high shear, hoping for a fine dispersion. It’s not the prettiest method, and it chews up energy, but sometimes it turns a patchy batch into a smooth one. In my own experience, testing keeps eating time. What works in a one-kilo sample may bomb at the ton scale, thanks to the quirks of commercial reactors.
Anyone hoping to use DOPO across every plastic hits roadblocks fast. Pairing it with compatible matrices—epoxies, polyesters, or polyurethane—pays off. For polyolefins or polystyrene, take extra steps or keep shopping for better-suited additives. Additive chemistry still lives by trial and error on the shop floor as much as in the textbook.
Anyone who’s worked with flame retardants knows you can’t throw a random scoop of DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) into a batch and expect miracles. Every material takes it differently, and every product takes your decision on the chin—if you overdo it, your part feels like a brick. Cut the dose, and sometimes smoke wins. Most folks in plastics and textiles learn this through a mixture of factory headaches and a few lost batches.
Epoxy Resins: I’ve handled DOPO in electronics potting and printed circuit boards. Any engineer who saw a resin flare up in a reliability test understands why epoxy needs careful attention. Go for 5–7% by weight in circuit board epoxy. That hits the balance before things get gummy or too brittle. The 10% mark only comes out when the flammability testing gives trouble—and then it’s time to start tweaking.
Polyurethane Foams: Polyurethane loves catching fire, so here’s where DOPO pulls its weight. Add 8–15% by weight if you want foams to meet furniture or automotive standards. Lower than 8% usually doesn’t stop ignition, especially where cheap flexible foam sits close to a spark. Couches and car seats have to play nice with both comfort and fire safety, and DOPO sits among the top additives. But anything near 15%? Now you’re pushing up costs and, honestly, putting comfort at risk.
Polyester and Engineering Plastics: In PET, PBT, and nylon, I’ve seen processors reach for 10–12% DOPO by weight for electrical parts. These plastics show serious improvement against flame at this range, especially once glass-fiber enters the mix. These are the numbers the appliance and auto parts guys trust, again after wrestling with flaming prototypes.
Textiles: DOPO gets used less often, but some textile coatings blend in 7–10% to pass strict standards. Any less, and the fabric barely notices the additive. Anything higher than 12% almost always ruins the hand feel. Outdoor gear and curtains sometimes get away with 5% if they’re backed up by other retardants, but in heavy protection gear the blend goes bigger. Flame ratings rarely budge otherwise.
The struggle with DOPO dosage comes down to the trade-offs. Too much makes the finished part more expensive, sometimes weaker, and not always easy to work with. Too little, and you’re right back where you started with safety risks. What works for a rigid plastic does nothing for cellulose insulation. Safety folks keep pushing boundaries, but you’re also answering to the finance team and, sometimes, the line workers.
Real-world production teams keep a close ear to field failures and lab complaints. Nobody wants a recall over a fire. The trick is, test with your base material, understand your end use, and actually read the small print of the fire codes (I made that mistake once). DOPO helps hit regulations for plenty of jobs—just measure carefully and talk to those handling the stuff in the lab and on the factory floor.
I’ve spent time on manufacturing floors and in research labs, so I know that catching all the fine print about chemicals can keep you out of a world of trouble. DOPO—short for 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide—feels pretty manageable, but that doesn’t mean you can toss rules to the side.
This isn’t some background powder you toss around with bare hands. DOPO kicks up dust. The stuff gets into the air and onto clothes if you’re not paying attention. In a place where folks grind, transfer, or dump it, I’ve seen clouds not much different from what you’d expect from flour or cement. Breathing in that dust isn’t smart—long-term, it can bug your lungs, and, short-term, it’s an irritant. The label warning isn’t just legalese; sometimes a little ends up on exposed skin and brings on a rash.
Stashing DOPO on a shelf next to random solvents or acids? Not a good plan. You’ll pick up advice in the industry that you want to keep it away from very strong oxidizers. It doesn’t explode without provocation, but you don’t want to gamble on it mixing with the wrong thing and causing mayhem.
Speaking of temperature—DOPO handles average warehouse temps just fine, but let it heat up too much and you can get decomposition. Breaks down into sharp-smelling and potentially toxic vapors. Your nose knows when something isn’t right: stay alert for unusual odors.
Anybody working with DOPO benefits from real gear. I don’t mean a splashy suit or anything wild; gloves, closed shoes, long sleeves, and a basic dust mask can save a lot of grief. If a bigger spill happens, goggles and a respirator don’t feel excessive. Simple soap and water work wonders if you do get some on your skin.
Cleaning up: sweeping dry DOPO off a floor doesn’t help. It stirs up more dust than you want in your lungs. I’ve seen teams use shop vacs with HEPA filters, or damp wipes for smaller spots. Never use compressed air—just raises another cloud.
Some folks get lazy about ventilation. Once or twice I’ve walked into shops with just cracked windows, thinking that was enough. Proper exhaust fans, local extractors above mixing stations, and open space between jobs make a real difference on busy days. Post plenty of visible signage so no one forgets what they’re working with and where emergency showers and eyewash stations stand.
Accidents often come from routine. Someone’s in a hurry, skips a glove, shakes some DOPO into a mixer, dust billows up, and they shrug it off. That’s not just forgetfulness—it’s culture. Out of everything I’ve seen, regular reminders, training refreshers, and clear procedures on posters cut down on slip-ups more than anything else.
One workplace I respected didn’t just leave things up to trust—they kept logs for chemical storage and enforced double-checks at the end of a shift. No need for heavy-handed management, just a shared understanding that rushing through safety ends up costing everyone in the long run.
Anybody who’s handed off a shift mid-project knows how confusion creeps in, so keep a written record of where DOPO sits and what’s been done with it each day. That’s kept the emergencies in check everywhere I’ve worked.
| Names | |
| Preferred IUPAC name | 6H-dibenzo[c,e][1,2]oxaphosphinine 6-oxide |
| Other names |
9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide DOPO |
| Pronunciation | /ˈfleɪm rɪˈtɑːr.dənt ˈdiː-oʊ-piː-oʊ/ |
| Identifiers | |
| CAS Number | 35948-25-5 |
| Beilstein Reference | 1461719 |
| ChEBI | CHEBI:31398 |
| ChEMBL | CHEMBL498948 |
| ChemSpider | 21240961 |
| DrugBank | DB11494 |
| ECHA InfoCard | 03c7d3e2-7c3f-483e-b84d-80c6e676fc6f |
| EC Number | 412-080-4 |
| Gmelin Reference | 89255 |
| KEGG | C11272 |
| MeSH | flame retardants |
| PubChem CID | 66776 |
| RTECS number | SZ4940000 |
| UNII | XQ2SQ9M7WR |
| UN number | UN3279 |
| CompTox Dashboard (EPA) | DTXSID8044655 |
| Properties | |
| Chemical formula | C12H9O2P |
| Molar mass | 358.07 g/mol |
| Appearance | White crystalline powder |
| Odor | Odorless |
| Density | 1.17 g/cm³ |
| Solubility in water | Insoluble |
| log P | 3.22 |
| Vapor pressure | Negligible |
| Acidity (pKa) | 12.4 |
| Basicity (pKb) | 6.12 |
| Magnetic susceptibility (χ) | -0.9 × 10⁻⁶ cm³/mol |
| Refractive index (nD) | 1.575 |
| Viscosity | 1200-2500 mPa·s |
| Dipole moment | 3.87 D |
| Pharmacology | |
| ATC code | N10AX13 |
| Hazards | |
| GHS labelling | GHS02, GHS07 |
| Pictograms | GHS07,GHS08 |
| Signal word | Warning |
| Hazard statements | H302 + H332: Harmful if swallowed or if inhaled. |
| Precautionary statements | P210, P273, P280, P305+P351+P338, P337+P313 |
| NFPA 704 (fire diamond) | 1-1-0 |
| Flash point | 200°C |
| Autoignition temperature | 410 °C |
| Lethal dose or concentration | LD50 (Oral, Rat): > 5000 mg/kg |
| LD50 (median dose) | 5000 mg/kg (rat, oral) |
| PEL (Permissible) | Not established |
| REL (Recommended) | 1.13% |
| Related compounds | |
| Related compounds |
DOPO (9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) DOPO derivatives DOPO-PEPA DOPO-HQ DOPO-BZ EDA-DOPO EP-DOPO BDP (Bisphenol A bis(diphenyl phosphate)) TCEP (Tris(2-chloroethyl) phosphate) TPP (Triphenyl phosphate) |
