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Oxalic acid caught the attention of chemists in the 18th century. Early work by Swedish chemist Carl Wilhelm Scheele remains one of the earliest records of its isolation, extracted from wood sorrel around 1776. Extraction from plant sources marked its beginnings, giving way to synthetic production methods during the Industrial Revolution. This transition unlocked broader access and dropped production costs, which led to industrial and laboratory applications that have persisted to the present day. Factories shifted from sourcing oxalate-rich plants to using more controlled chemical synthesis, particularly since the 19th century. That move helped anchor its role as a standard reagent and a workhorse in various sectors.
Oxalic acid dihydrate stands as a commonly used solid organic acid. With its colorless, crystalline appearance, it dissolves easily in water, furnishing two molecules of water per molecule of acid. The substance finds a steady spot in chemical inventories, acknowledged for its reactivity and relatively inexpensive production. Most users know it as a cleaning and bleaching agent, a specialist in removing iron and rust stains, and a key participant in chemical synthesis. The chemical is rarely seen in its anhydrous form outside specialty laboratories; the dihydrate provides a stable, manageable form that remains the backbone of day-to-day applications.
A closer look at this compound's properties reveals a dense, crystalline structure with a molecular weight around 126 grams per mole. The crystals dissolve readily in water and alcohol, which makes mixing and preparation straightforward in most lab and industrial settings. It melts at temperatures just above 100°C, losing water of crystallization along the way. Chemically, it's a strong reducing agent and exhibits acidity comparable to many mineral acids, although it's less aggressive than hydrochloric or sulfuric acid. This balance between reactivity and ease of handling draws chemists to oxalic acid when seeking a tool that's powerful, yet controllable.
Product labeling makes a difference in safe storage and use. Suppliers provide materials with standard purity grades, usually ranging from 99% to technical or industrial grades around 97%. Labels list the chemical formula (C2H2O4·2H2O), hazard classifications, and recommended handling instructions. Batch numbers, shelf life, and storage conditions also feature prominently. Containers keep the substance dry and protected from contamination, with opaque, tamper-evident packaging to guard against moisture absorption and accidental exposure. Accuracy in labeling supports regulatory compliance, helps prevent cross-contamination, and builds trust between producers, sellers, and end-users.
Earlier, natural extraction dominated, but producers soon turned to chemical synthesis. Today’s main method involves the oxidation of carbohydrates such as glucose using nitric acid in the presence of a catalyst. Some processes start from sugar beets, while others rely on sodium formate that gets oxidized under specific conditions. Industrial plants prefer synthesis routes that reduce waste and energy use while yielding high-purity product. Process engineers monitor impurities closely, especially since even minute metal contamination alters both performance and safety in certain applications. Stepwise filtration and crystallization ensure the final material meets tight quality expectations.
Oxalic acid dihydrate takes an active role in chemical reactions. Its ability to act as both a reducing agent and a chelator makes it well-suited for complexing metal ions, precipitating calcium, and lowering certain metal concentrations in solution. Many chemists use it to clean laboratory glassware stained with manganese dioxide or ferric iron. The acid decomposes on heating, producing carbon monoxide, carbon dioxide, and water. It donates protons easily, creating oxalates when combined with various metal salts. In organic synthesis, the compound helps tailor molecular structures, modify surfaces, and break down unwanted residues with remarkable efficiency.
Across industries and catalogs, oxalic acid dihydrate carries multiple names. Common synonyms include ethanedioic acid dihydrate, acid of sugar, and oxalate acid. Some commercial labels shorten the name to “oxalic acid crystals," reflecting the product’s preferred handling form. Scientific suppliers often stick with IUPAC terminology, but industry jargon may include more colloquial terms. The diversity in naming can lead to confusion in procurement, so referencing CAS numbers (6153-56-6) sidesteps ambiguity. Whatever the name, this substance delivers a consistent spectrum of chemical functions.
Oxalic acid dihydrate isn’t without its dangers. Contact with skin or eyes produces irritation, and ingestion is poisonous due to its calcium-chelating effect, which can lead to hypocalcemia and kidney damage. Inhalation also causes respiratory irritation, particularly in poorly ventilated spaces. Facilities rely on strict handling guides: gloves, safety goggles, and proper clothing come standard. Engineering controls ensure that dust and vapors don’t build up, and first aid stations provide antidotes for accidental exposures. Storage requires sealed, clearly labeled containers, placed away from incompatible chemicals like strong bases and oxidizers. Training and emergency drills keep workers prepared. I remember early lab work where oxalic acid landed on my hand—hours later, I found a mild rash, a reminder of how crucial protective gear and prompt rinsing remain in real-world use.
The versatility of oxalic acid dihydrate shapes its place in industry and research. Metalworking shops rely on it for rust removal and metal surface preparation before painting or plating. Textile manufacturers use it to bleach and clean fabrics, giving bright finishes without damaging fibers. Woodworkers wipe away stains from oak, walnut, and other hardwoods, restoring aged furniture. In analytical chemistry, its chelating ability helps determine calcium content in solutions by precipitating calcium oxalate. Some hobbyists clean mineral specimens with it, revealing crystal beauty without harsh abrasion. Its presence in pharmaceuticals, though limited, turns up during synthesis of certain antibiotics and as a pH adjuster. Home users lean on oxalic acid to remove mineral buildup and stubborn stains, but safe handling separates the professionals from the untrained, as even a simple task can twist into a hazard.
Recent years brought renewed interest in oxalic acid as a stepping-stone toward greener production processes. Researchers look for bio-based methods using enzymatic or microbial conversion from agricultural byproducts, lowering energy needs and cutting toxic byproducts. Exploration into electrocatalytic synthesis—where electrical energy replaces chemical oxidants—could further slash emissions. The hunt goes on for tailored derivatives that retain oxalic acid’s cleaning abilities with less acute toxicity. Complexation with metal ions offers promising pathways in catalysis, battery technology, and even rare earth element recycling. Graduate students and postdocs in chemistry, materials science, and environmental engineering turn to this compound while hunting for breakthroughs that rethink tradition and challenge established production routes.
Medical and environmental studies mark oxalic acid as a substance worthy of caution. Its low LD50 in humans and animals reflects its threat to the kidneys, bones, and nervous system if swallowed or absorbed in large amounts. Repeated or chronic exposure magnifies these risks—think of situations where workers might handle the compound day in and day out, or spill it, raising dust that nobody sees. Toxicologists track pathways from accidental consumption, skin absorption, and inhalation. Wastewater treatment systems look at oxalic acid loads with concern, as its persistence and reactivity disrupt normal water chemistry and impact aquatic life. Antidote development and medical protocols for acute exposures improve every decade, thanks in part to long-running case studies and poison control data sharing from labs, clinics, and hospitals all over the world.
Innovation rarely leaves established chemicals behind, and oxalic acid offers no exception. Researchers focus on uses in lithium-ion battery recycling, recovering valuable metals through selective chelation. Water treatment applications take shape, promising to capture heavy metals or break down persistent organic pollutants. Improvements in plant-based production could stem from advances in synthetic biology, harnessing engineered microbes to deliver cleaner, cheaper supplies. As environmental policies grow stricter, safer formulations and handling protocols keep pace. Manufacturers keep an eye on packaging advances that reduce accidental contact and food supply risks. This decades-old acid still finds ways to stay relevant, growing from a laboratory curiosity into a factory staple, a cleaning agent, and a symbol of chemistry's reach across old problems and new frontiers.
Growing up, I didn’t think much about chemical names—until I realized the strange-sounding “oxalic acid dihydrate” actually showed up in my home. This compound turns up under sinks, in vegetable patches, even in the metalwork shed. Most folks see chemistry as something sealed off in labs, but oxalic acid dihydrate drifts into plenty of daily routines, making life easier while seeking a careful balance with safety.
My earliest encounter with oxalic acid dihydrate came as a white powder that claimed it could brighten up rusty tools. And sure enough, after mixing with water and scrubbing just a bit, years of rusty stains seemed to dissolve. This acid doesn’t just deal with rust, though. Many cleaning products targeting stubborn mineral deposits or ink stains owe their punch to oxalic acid. I’ve used it on old porcelain to vanish yellowing marks, and on patio stones where hard water left ugly trails.
Of course, you don’t just sprinkle this stuff everywhere. Its effectiveness calls for respect—a gloved hand, a good rinse, ventilation. It’s less forgiving than your gentle dish soap, but with preparation, it saves elbow grease and headaches alike.
Anyone who gardens in areas packed with acidic soil will likely have come across oxalic acid’s role in keeping plants healthy. It turns up as a natural component in spinach and rhubarb leaves, but even more important, some gardeners use it—carefully—to treat bee colonies for varroa mites. This practical solution comes backed by research: the United States Department of Agriculture notes oxalic acid as a trusted mite control option for beekeepers when synthetic chemicals threaten hive health.
There’s a catch, though—too much will harm both bees and plants. Every gardener or beekeeper ought to pay attention to dosage, timing, and application. As with any strong tool, a little education turns oxalic acid from an unapproachable chemical to a reliable fix.
Restoring old furniture and fixtures gets tricky when metals and stones start to lose their shine. Oxalic acid dihydrate’s ability to break down iron stains during woodworking breathes new life into vintage pieces. Antique dealers and DIYers swear by it for furniture that has picked up water rings or darkened patches from old nails.
In the stone industry, I’ve watched workers soak deeply stained marble and granite with a diluted oxalic acid mix, then buff the surface back to something close to its original look. Extreme care pays off—the wrong concentration damages more than it cleans—so experience and proper instructions matter here.
With experience comes caution. Oxalic acid dihydrate, for all its utility, can cause irritation or worse if left unchecked. The Centers for Disease Control and Prevention highlight the risks to skin, eyes, and lungs. Storage away from kids and pets matters as much as proper use. Wastewater from cleaning or restoration needs responsible disposal since this acid can disrupt both plumbing and natural waterways.
Some manufacturers have switched to less aggressive alternatives in household products, but for tough stains and specialized jobs, oxalic acid still gets the call. Anyone reaching for it ought to read labels, follow official safety advice, and recognize that leaning on chemical helpers is not about shortcuts but smart, respectful problem-solving.
Oxalic acid dihydrate often pops up in everyday life more than people think. Whether it's cleaning minerals off rocks, descaling coffee machines, or brightening old wood, this crystalline powder pulls a lot of weight around the house and in industry. People see it marketed as a handy solution but that doesn’t always spell “harmless.” My own experience rewinding a rusty garden tool left me wishing I’d been more careful with the powder — red fingertips and a bout of sneezing set me straight.
Oxalic acid dihydrate brings solid chemistry to a project but carries real risks. The main worry comes from how it behaves once you begin mixing or using it. Dust rising off a scoop can irritate lungs. It’s not the worst toxin you’ll ever meet, but skin and eyes react fast to even small amounts. More than a few cases exist where quick jobs in the garage ended with red rashes or a burning feeling in the eyes.
Numbers tell the safety story. The LD50 for rats clocks in around 375 mg/kg, meaning a few grams could harm small bodies. Get this stuff on your hands or in your eyes and the reaction is quick: a stinging, tingling, sometimes burning sensation, plus the risk of longer-term skin trouble if you don’t wash it off. Breathing in dust can leave your throat scratchy or your breathing wheezy for a while. It's not as risky as strong acids like hydrofluoric, but respect for personal protection matters here.
Leaving oxalic acid sitting open next to snacks or kids feels like tempting fate. Children can mistake the crystals for sugar. Pets can lap up a spill. Even adults make mistakes—one slip and a quick lunch comes with a dose of acid. Poison control centers report accidental exposure every year, sometimes with serious results.
Oxalic acid builds up problems in the body over time. The kidneys work hard to clear it out, but too much too fast can lead to kidney stones or even kidney damage. This risk increases for folks with existing kidney issues or those taking certain medications. People who prepare food in cast iron cookware or eat lots of rhubarb leaves have had brushes with oxalate trouble; add careless handling of the chemical, and the risk doubles.
Simple tools make a difference. A dust mask helps keep particles out of lungs during mixing. Nitrile gloves keep skin safe. Goggles prevent stinging eyes or worse. A few minutes of preparation saves hours of regret. Always open the container slowly, away from your face, and mix with water in a well-ventilated space. Never store oxalic acid near food or drinks.
If a spill happens, clean it up with plenty of water and keep pets or children out until everything is dry. Never pour oxalic acid down pipes without a lot of dilution — concentrated stuff can harm plumbing and septic systems. Read labels and safety data sheets. Over-the-counter cleaning products often list how much acid they contain, but don’t assume a weaker formulation erases all risk.
Healthcare professionals and toxicologists recommend safe disposal of leftovers. Used solution should go to hazardous waste collection sites. Homemade solutions left out find their way into curious hands; accidents rise when chemicals hang around. Safe habits build a safer home, plain and simple.
Oxalic acid dihydrate is more common than most folks think. Aside from its place in chemistry lab cupboards, it pops up in cleaning supplies and even has its name tied to a few old-fashioned wood-bleaching tricks. It looks almost innocent—white crystals or powder. Yet the risks are real. Getting careless with it, even for a moment, has consequences nobody wants to face. It can damage skin, burn the eyes, and if inhaled, create serious breathing trouble. Handling it day in and day out really drives the lesson home: storing it safely isn't overcautious; it's basic self-respect and responsibility for others around you.
Oxalic acid dihydrate holds onto water molecules. Exposing it to the air, especially damp air, ruins its quality and makes it clumpy. Once, I left a container out too long during a classroom demo—the crystals turned soggy and stuck to the scoop. Lesson learned. Always tighten the lid right after use. A tightly sealed, acid-resistant container (HDPE plastic or glass with a good cap) goes a long way. I keep mine in a dry cabinet, never near open sinks or where spills might get splashed with water—moisture is the enemy of both safety and stability.
Many chemicals break down faster in summer heat or near windows, and this one is no different. I keep containers in a cool spot—room temperature or cooler if possible. No direct sun, not next to radiators or ovens. Heat shortens shelf life, yet the big risk is a container getting extra pressure from heat and moisture combined. Sometimes folks forget how easy it is for a storeroom to heat up, especially in older buildings without good circulation. A thermometer in the cabinet helped me learn just how hot things could get. The peace of mind is worth the trouble.
I’ve seen too many bottles with faded handwritten scribbles. Use real labels. Put the full name, the concentration or form, and the date the container was opened or repackaged. Make sure every person in the workspace gets the message: don’t take shortcuts, especially with potent stuff like oxalic acid dihydrate. Once, a colleague grabbed the wrong substance due to poor labeling—thankfully, nothing bad happened, but the scare kept everybody more diligent. Good labeling isn't about red tape—it saves fingers, eyesight, and sometimes lives.
There’s science, regulation, and then there’s everyday life. Keep oxalic acid dihydrate locked away, far from children, pets, and foods. Store it far from bases, oxidizers, or any reactive chemicals. In my house, the cleaning closet stays out of reach for good reason—the risk isn’t theory, it’s real and present. If a spill does happen, I keep plenty of water, gloves, and masks at hand, plus clear written instructions for everyone in the household. These habits grew out of stories passed down from old-timers and a few close calls of my own. Simple steps keep a minor risk from turning into tomorrow’s front-page news.
Oxalic acid dihydrate pops up in labs, cleaning products, metal treatments, and even in certain household stain removers. People often overlook its risks, thinking anything so common can’t be dangerous. That mindset can get someone in trouble. As someone who’s worked in both labs and DIY home environments, I’ve seen the difference good information makes when dealing with chemicals like this one.
Direct contact can trigger intense irritation on skin—itching, redness, even burns if left too long. Eyes? It stings and can damage vision. In one laboratory project, a single careless moment led to a painful lesson for a colleague handling oxalic acid without proper gloves. Simple gloves and goggles prevented a repeat, but not everyone gets a second warning.
Breathing oxalic acid dust or mist attacks the throat and lungs. Even a small hit can spark coughing or wheezing, while heavier exposure causes chest pain and shortness of breath. People with asthma or breathing conditions take an even bigger risk. The key lesson I've learned is that a cheap dust mask can make a huge difference, and proper ventilation always matters much more than it seems until something goes wrong.
Accidental ingestion proves much worse. Even a teaspoon can poison the body. Oxalic acid binds with calcium inside you, forming crystals that clog kidneys and nerves. Nausea, vomiting, muscle cramps, and heart trouble show up fast. Unattended children or pets around cleaning products face the highest danger, so storing chemicals high and locked away in labeled containers becomes the only sensible move.
Some people wash oxalic acid solutions straight down the drain—after all, it looks like water. This damages aquatic life, as oxalic acid can lower water pH and kill small organisms. I’ve found that local waste disposal rules often ask for neutralizing acids with baking soda before disposal, and for good reason. Keeping chemicals out of water should never feel optional.
Alone, oxalic acid won’t burn easily. It still poses a fire hazard if heated or mixed with strong oxidizers, creating toxic gases like carbon monoxide and carbon dioxide. Any fires involving this chemical bring a risk of poisonous smoke; firefighters wear protective gear for a reason here.
Education lowers risk. Always label and store chemicals in the original containers. Proper gloves, goggles, and masks should sit right next to any bottle or package. If a spill happens, don’t reach for water first—neutralize it and clean up with care. Anyone using it at work or home really benefits from checking the Safety Data Sheet every time, even if they’ve used it before.
No one expects an accident, but knowledge and a few habits go a long way. Oxalic acid dihydrate deserves real respect to avoid real pain—both for people and the wider environment.
Anyone who has worked in a lab or dabbled in certain cleaning or metal restoration jobs probably met oxalic acid dihydrate. Its crystal form flows out of containers looking harmless as table sugar, but don't let that fool you. Touch it, breathe it, or pour it down a drain without a second thought, and you might end up with far more problems than a dirty workbench or stained wood. Oxalic acid can damage tissue on contact and harm aquatic life once it's in the water supply. Handling it calls for smart choices grounded in real safety measures.
I remember the old days of science labs, where disposal sometimes meant flushing things down the drain—out of sight, out of mind. With toxic or corrosive compounds like oxalic acid dihydrate, that's reckless. Once it enters the sewer, oxalic acid can lower the pH of water, corrode plumbing, and head straight to municipal treatment plants. Those facilities don’t filter out everything, especially chemicals designed to be tough on rust or tough on stains. Oxalic acid also chelates with calcium and iron—essential minerals for fish and plants—making a mess of local waterways. The bigger harm comes to people and animals downstream.
Splash goggles, gloves, and proper ventilation come first. If there's even half a chance for a chemical to harm skin or lungs, don’t skip these basic steps. If you don’t have the original container or label, write a clear one. People often run into problems years later, trying to remember which white powder is which.
If you have a small, dilute leftover—say, lab glassware rinses—a simple neutralization does the trick. Add baking soda (sodium bicarbonate) a bit at a time to your dilute solution. Stir gently. You want fizz but not a cauldron’s worth of foam. Check with pH paper as you go; the goal is near-neutral (pH 6-8). This reaction forms carbon dioxide, water, and sodium oxalate, which is much less hazardous. Only once it reads neutral on pH paper should you consider pouring down a drain, and only if your local wastewater utility allows for it. In many places, rules have tightened. Call or consult your local hazardous waste department before letting anything go.
Bigger jobs or solid residue? Skip the DIY approach. Cities and counties hold hazardous waste collection events, or offer drop-off centers. Package the material in a sealed, labeled container and keep it away from heat or anything reactive. Let trained professionals take it from there—they'll make sure it ends up at a treatment facility equipped to neutralize toxic materials correctly. Some universities and companies have waste disposal contracts and will accept these small quantities if you ask nicely and follow guidelines.
Oxalic acid sees use in a lot more than chemistry sets—think wood restoration, rust removal, even some specialty cleaning products. If you work with it, buy only as much as you know you’ll use, to minimize leftovers. Watch out for accidental mixing with bleach or other strong oxidizers, which can release dangerous gases and make things worse. Store it locked up, with clear warnings for anyone who might encounter it down the line. Keep those basic habits up, and you’ll protect not only your drains and pipes, but your neighbors, local wildlife, and the people downstream who depend on clean water.
| Names | |
| Preferred IUPAC name | oxalic acid dihydrate |
| Other names |
Ethanedioic acid dihydrate Oxalate acid dihydrate Oxiric acid dihydrate |
| Pronunciation | /ɒkˈsæl.ɪk ˈæs.ɪd daɪˈhaɪ.dreɪt/ |
| Identifiers | |
| CAS Number | 6153-56-6 |
| Beilstein Reference | 1366778 |
| ChEBI | CHEBI:30842 |
| ChEMBL | CHEMBL1376 |
| ChemSpider | 744 |
| DrugBank | DB09409 |
| ECHA InfoCard | 03d248e2-41b1-4915-9e93-baf4c32db47e |
| EC Number | 205-634-3 |
| Gmelin Reference | 131132 |
| KEGG | C00209 |
| MeSH | D000113 |
| PubChem CID | 61451 |
| RTECS number | RN7700000 |
| UNII | QXO1B6X370 |
| UN number | UN3261 |
| Properties | |
| Chemical formula | C2H2O4·2H2O |
| Molar mass | 126.07 g/mol |
| Appearance | White crystalline solid |
| Odor | Odorless |
| Density | 1.65 g/cm³ |
| Solubility in water | Soluble in water |
| log P | -1.76 |
| Vapor pressure | 0.7 mmHg (at 25 °C) |
| Acidity (pKa) | 1.27 |
| Basicity (pKb) | 1.27 (pKb1), 6.37 (pKb2) |
| Magnetic susceptibility (χ) | χ = -72.0 × 10⁻⁶ cm³/mol |
| Refractive index (nD) | 1.439 |
| Dipole moment | 3.97 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 155.3 J⋅mol⁻¹⋅K⁻¹ |
| Std enthalpy of formation (ΔfH⦵298) | -1623.5 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | –1102.0 kJ/mol |
| Pharmacology | |
| ATC code | V03AN01 |
| Hazards | |
| Main hazards | Harmful if swallowed, causes skin and serious eye irritation, may cause respiratory irritation. |
| GHS labelling | “GHS05, GHS07, Danger, H302, H312, H315, H318, H319, H332, P264, P280, P301+P312, P302+P352, P304+P340, P305+P351+P338, P332+P313, P337+P313, P362+P364, P501” |
| Pictograms | GHS05,GHS06 |
| Signal word | Warning |
| Hazard statements | Harmful if swallowed. Causes serious eye irritation. |
| Precautionary statements | P264, P270, P301+P312, P330, P501 |
| NFPA 704 (fire diamond) | 2-3-1 |
| Autoignition temperature | 230 °C |
| Lethal dose or concentration | LD50 Oral Rat: 7500 mg/kg |
| LD50 (median dose) | LD50 Oral Rat: 7500 mg/kg |
| NIOSH | WV7350000 |
| PEL (Permissible) | PEL (Permissible Exposure Limit): 1 mg/m³ |
| REL (Recommended) | 1 mg/m³ |
| IDLH (Immediate danger) | 500 mg/m³ |
| Related compounds | |
| Related compounds |
Oxalic acid Sodium oxalate Potassium oxalate Ammonium oxalate Calcium oxalate |
