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My first encounter with 1-Hydroxybenzotriazole Hydrate, or HOBt as many in the lab call it, left me struck by its legacy in peptide chemistry. HOBt’s story winds back to the 1960s, a period when synthetic chemists pored over new ways to assemble peptides without sending yields into the gutter. In those days, the world watched the field of protein synthesis break from simple dipeptides to full-sized chains. Problems like racemization refused to budge, threatening purity and efficiency. The arrival of HOBt in peptide coupling gave researchers a new handle, helping streamline peptide bond formation. This hydrazine was no accident—driven by pressing issues in life science research, chemical companies and academic groups shaped HOBt into an indispensable reagent for activating carboxylic acids, smoothing out the stubborn bumps in solid-phase synthesis.
In modern organic chemistry, HOBt does not need an introduction for professionals who make peptides or modify proteins. Chemists look for substances that boost yields, reduce byproducts, and pump up selectivity. HOBt ticks those boxes with a structure that disrupts side reactions and suppresses racemization—a real pain for anyone piecing together a long peptide. For some, HOBt stands as a go-to reagent, carried in labs and stockrooms across big research campuses. Its reputation does not rest on marketing spin but on decades of results, trialed and proven in countless reaction flasks.
On a shelf, HOBt hydrate takes up little space. It forms colorless to off-white crystals, with a faint, earthy smell that reminds me of days in the undergraduate teaching lab. Solubility in water and most polar organic solvents means it slips right into many reaction mixtures without fuss. HOBt packs just enough stability to store at room temperature, though stray sparks or high heat spell danger—HOBt’s notoriety for explosiveness persists if you let it dry out and mishandle it. Chemists keep a respectful distance, treating it with care and good judgment.
You spot HOBt hydrate labeled with reference to both its formula and its water content. Laboratories source it in purity levels above 98 percent, written clear and bold on containers. Packaging carries stark warnings in bright colors, which do more than decorate: they remind anyone reaching for HOBt to think twice and double-check storage, since careless handling could trigger decomposition or worse. My own practice: I never leave it out in open air longer than necessary, and I log its use in the chemical inventory as soon as the vial returns to the desiccator.
The process that makes HOBt reflects practical chemistry at its best. Most commercial samples rise from reactions between o-phenylenediamine and nitrosating agents under controlled conditions. Some wish to run small-batch synthesis in the lab, especially when tighter control over impurities matters. It takes patience, knowledge, and the right apparatus to get HOBt out of those reactions cleanly. By the end, the hydrate generated often includes water of crystallization, which gives the compound a little extra stability and marks the difference from its anhydrous, far more dangerous cousin.
The central contribution of HOBt comes from its knack for forming activated esters, especially in peptide synthesis. Combined with carbodiimides like DCC or EDC, HOBt forms intermediates that speed up amide bond formation, dodging racemization and making peptide chains grow efficiently. My own experiments paired HOBt with coupling reagents, watching difficult segments assemble without junk byproducts. Chemical creativity does not stop there—some clever researchers swapped in HOBt for other coupling steps, fine-tuning selectivity or controlling energetic intermediates in pharmaceutical syntheses.
Walk through chemical catalogs, and you will see HOBt listed as 1-Hydroxybenzotriazole hydrate or simply Hydroxybenzotriazole. Its registry number, 123333-53-9 for the hydrate, offers a shortcut for those who search by numbers. Some older literature leans on names like Benzotriazol-1-ol, especially in European texts, but the abbreviation “HOBt” is shorthand lab slang almost everyone understands.
Ask any lab manager about handling HOBt and you will get a list of firm rules. HOBt has shown a tendency to go unstable, especially once dried or mishandled. The hydrate version reduces some risks, but safety steps deserve strict attention. Goggles, gloves, and solid ventilation stay non-negotiable. Institutions train staff to store HOBt away from heat and sources of ignition, log its inventory, and control quantities to limit hazard in case something goes wrong. Once, a colleague had to dispose of a larger batch—this prompted a call to hazardous waste professionals rather than a rush job down the drain. For regulators, HOBt ranks on lists of controlled chemicals in several countries, which shapes its ordering, transport, and disposal. Anyone using it needs up-to-date risk assessments on hand before breaking open even a fresh bottle.
In applications, HOBt came of age as a peptide coupling additive, moving from a specialty item in life sciences to a backbone for protein engineering, diagnostics research, and emerging biotech startups. Researchers synthesize custom peptides or oligonucleotides for cancer research, enzyme design, antibody development, and vaccines—each one resting on the foundation HOBt helped lay through its suppression of racemization and ability to tackle difficult couplings. Manufacturers of specialty chemicals and pharmaceuticals rely on HOBt chemistry when bringing delicate molecules off pilot-scale benches and into full manufacturing. HOBt plays a part shaping fluorescent probes, peptidomimetics, and some classes of novel antibiotics. As someone who ran peptide syntheses for neuroscience projects, I depended on HOBt to unlock peptide designs that standard reagents would never finish cleanly.
R&D in peptide chemistry moves at full pace, and HOBt remains a reference point in studies aiming to streamline old protocols or swap in safer, greener alternatives. Green chemists talk about cutting out hazardous byproducts, reducing waste, and dialing back hazardous solvents—goals rarely easy to fit with established chemical tools. Studies turn to HOBt analogs, seeking those which keep activation power while reducing explosive hazards. Laboratory groups share their latest tweaks, from flow chemistry set-ups incorporating HOBt to local efforts on scaling production for large, high-purity batches. Newer ways to handle and recycle this compound win grants, attract startups, and sometimes generate patents for safer production and consumption.
Evidence does not paint HOBt as the biggest villain in chemical labs, but the risks are real and non-trivial. Researchers flagged both acute and chronic toxicity risks, especially when inhaling dust or after accidental skin exposure. Animal studies yielded mixed results on long-term exposure, though environmental impact remains a point of active scrutiny. Water treatment facilities keep a watchful eye for HOBt waste traced from pharmaceutical manufacturing or research campus run-off. Regulatory agencies urge companies to introduce clean-up protocols that keep HOBt and its derivatives away from the water table. The drive for non-hazardous analogs flows partly from such studies. As someone who once handled spills miles away from the waste depot, I see the logic in keeping HOBt confined to smallest necessary batches.
Forecasts for HOBt circle around safety upgrades and creative rethinks in peptide chemistry. Academic groups and industrial chemists push hard for drop-in replacements that trim down risk, offer equal or better selectivity, and fit tougher safety standards. Regulatory pressures play a huge part here as governments tighten oversight of energetic chemicals. On the other hand, no perfect substitute knocked HOBt out of its stronghold just yet. In hands of careful chemists, and with smart packaging and rigorously followed protocols, HOBt looks set to stick around wherever new peptide drugs or advanced biomolecules need assembling. I expect to keep seeing it—handled with respect, designed for performance, referenced in textbooks and cutting-edge research.
Some folks hear “1-Hydroxybenzotriazole Hydrate” and get lost in the name. To chemists, this compound matters because it makes a difference in how complex molecules come together. In the lab, I’ve watched researchers spend long hours optimizing peptide synthesis. The reagent we’re talking about—often shortened to HOBt hydrate—keeps reactions moving smoothly and helps boost yields. It’s not as well-known as table salt, but in my years around research benches, it’s been just as essential in some projects.
HOBt hydrate stepped into the spotlight because making peptides—chains of amino acids—is tricky without help. Anyone who’s tried to build proteins from scratch knows roadblocks pop up fast: side reactions, slow steps, or flat-out failed attempts. HOBt hydrate fixes common pitfalls, especially during the coupling of amino acids, the process where you try to lock individual building blocks together. This compound doesn’t just speed things along, it tampers down unwanted by-products. The difference shows itself in the cleaner end results and fewer headaches for people purifying their final product.
Safety also matters in the lab, and many older reagents weren’t great in that department. Traditional coupling agents developed a reputation for causing allergies, sometimes even explosions. HOBt hydrate improved the scene by reducing the risk of side reactions that led to dangerous gases or unstable mixtures. Laboratories everywhere started to keep it on hand, not just for the chemistry but for peace of mind.
Peptides sit at the center of research into new drugs, improved diagnostics, and even vaccines. HOBt hydrate makes those projects possible at a scale that works for both big-name pharmaceutical companies and small academic labs. Its main job is straightforward: it boosts efficiency and reliability in building peptide bonds. One example involved a colleague who struggled for a week to get a stubborn sequence to form; bringing in HOBt hydrate helped push the process across the finish line. A whole industry of custom peptide factories relies on it to hit deadlines.
Beyond the peptide world, chemists have found uses for this compound in refining certain chemical transformations. It’s found its way into the toolbox for creating more complex organic molecules—especially where more predictable outcomes are a must.
There’s always a trade-off in chemistry. HOBt hydrate is safer than some older coupling agents, but it isn’t free of hazards. The dry form has a risk of catching fire, so most labs use the hydrate version, which is more stable. Still, any chemical should be respected, and good ventilation, personal protective equipment, and careful disposal all play a part in responsible handling. Training new researchers about these risks shows a real commitment to safety and helps keep science moving forward without causing harm.
Researchers keep seeking new solutions. Over the years, some have tried replacing HOBt hydrate with greener, less hazardous options, or with reagents that work under milder conditions. The field moves quickly, and improved protocols seem to appear every few years. Still, for now, I see HOBt hydrate holding a solid spot in many labs’ workflows because the benefits outweigh the drawbacks for a lot of essential work.
1-Hydroxybenzotriazole Hydrate, known in labs as HOBt, shows up in peptide synthesis jobs all over the world. Its role is crucial, but folks who work with it come across some genuine safety concerns. This compound poses risks for fires and explosions, especially since dry HOBt takes just a little heat or friction to set off trouble. A straightforward oversight, like dropping a dry spoonful on a hot plate, can go from a small spill to a full-blown emergency.
You put on gloves and goggles every day, but with HOBt, this habit goes from routine to non-negotiable. The dust can irritate skin, and even a splash spells discomfort for your eyes. A proper lab coat fits the bill, shielding everyday clothes and skin from accidental spills. Change gloves right after handling the chemical, even if you think there’s no visible residue.
Nobody wants to breathe in fine chemical powder. With HOBt, dust can float around the workspace. It helps to handle it in a fume hood, so the air stays clean and your lungs protected. Wearing a mask isn’t just about following the rules—the goal is to walk away from your shift as healthy as you arrived. People sometimes forget, a few whiffs over weeks and months add up.
Moisture changes how this chemical behaves. HOBt Hydrate loses water when exposed to dry air, and once it dries out, it gains extra sensitivity to heat and sparks. That’s why you store it sealed tight, somewhere cool, where humidity stays steady. Silica gel packets inside the cabinet add an extra layer of backup, soaking up loose moisture. Storing it away from open flames or sources of heat needs no debate.
If some product spills, sweeping does more harm than good—dust flies everywhere, which nobody wants. Use a damp paper towel or a clean, moist cloth so particles cling instead of floating. Toss used clean-up materials as hazardous waste, not in regular trash, because small amounts can still pose threats if they ignite. Talk to the waste disposal team to confirm the labeling and containers are right—the goal is peace of mind for everyone who comes near that bin.
Sometimes working in a lab turns into autopilot, but HOBt keeps you on your toes. The compound has a record of accidental fires and even injuries, some documented in safety bulletins and chemical incident reports. It’s not a warning to stop using it, but a sign to respect protocols. Regular training refreshers, posters near storage cabinets, and simple checklists do more than decorate the lab. They push best practices front and center, so new hires and seasoned scientists both stay careful.
Chemical safety doesn’t rest on one person’s shoulders. I’ve seen teams that share their tips freely keep their incident numbers down. Labeling containers, keeping up-to-date safety data sheets, and holding open-door safety talks help everyone work with less risk. Looking out for each other in the workplace culture means a spill, exposure, or fire doesn’t catch anybody off guard. In the end, using HOBt responsibly makes the science safer for everyone—inside and outside the lab.
Chemists often talk about the need for clarity in the lab. No one likes accidentally mixing up ingredients, especially when safety or research money is on the line. Chemicals often sport long, tricky names. Here’s where a CAS number really helps. For 1-Hydroxybenzotriazole Hydrate, this number is 123333-53-9. It doesn’t sound fascinating at first glance, but this identifier makes global conversations about safety and quality a lot easier.
CAS numbers work as a universal language for researchers, suppliers, educators, and regulators. My own experience with undergraduate chemistry showed how easy it is to confuse chemicals based on names alone. In the digital catalogs and Material Safety Data Sheets, numbers cut out that confusion. A quick search for 123333-53-9 narrows the focus, whether you’re buying, researching, or checking toxicity reports.
1-Hydroxybenzotriazole Hydrate plays a role in peptide synthesis and serves as an intermediate in organic chemistry. Get the wrong substance due to a naming slip, and that can ruin weeks of work or compromise safety. In one instance, a lab I worked in received a shipment with similar names printed. Double-checking the CAS number prevented an expensive setback.
Researchers also rely on these identifiers for compliance. Regulatory agencies use CAS numbers to track dangerous or restricted chemicals. Laboratories must keep records precise not just for reproducibility, but to pass audits or meet environmental and workplace safety laws. For students and newcomers, learning to trust and use CAS numbers gets drilled in early. It’s a way of staying safe and accountable.
Companies spend millions managing risk in chemical supply chains. Quality control teams reject products not matching the right CAS label, preserving brand reputation. I remember an incident where a contaminant slipped through, mainly because two compounds had overlapping street names. Fast tracking the investigation started with matching CAS numbers.
The conversation doesn’t end in the lab. Even fire departments and poison control centers train to identify substances by CAS number. Querying a chemical emergency database with 123333-53-9 pulls up safety data in seconds, which makes emergency responses much more effective. That level of speed and accuracy saves lives.
Of course, not every smaller lab or startup gives CAS numbers the emphasis they deserve. Simplifying chemical inventories and digitalizing MSDS references would help. There’s also an argument for more training when onboarding lab workers. Putting CAS numbers front and center during purchasing, waste management, and research documentation builds a habit of accuracy.
Online chemical suppliers can reinforce practices here. More user-friendly platforms show CAS numbers right next to product names, making searching and ordering less prone to error. It’s one digit, but it can mean the difference between a successful experiment and a hazardous incident.
If more people see the CAS number as a safety net, chemical handling across schools, labs, hospitals, and companies stands to improve. The identifier 123333-53-9 for 1-Hydroxybenzotriazole Hydrate isn’t just a string of numbers on a label—it’s a tool that supports better communication, quality, and safety every step of the way.
Anyone who has worked with chemicals knows a careless moment can spell trouble. 1-Hydroxybenzotriazole Hydrate, or HOBt hydrate, is often found in peptide synthesis or fine-chemical manufacturing. A quick look at its history uncovers serious safety challenges. Over the years, the dry form has shown a tendency to catch fire or decompose with a bang. The hydrate form brought much-needed safety improvements, but that does not mean you toss it in a drawer and forget about it.
Dry HOBt showed a knack for going off with the right trigger—heavy friction, heat, or static charges. The hydrate form, loaded with water molecules, dials down that risk. From personal lab experience, bottles with the hydrate label offer a sense of relief, especially for those who have seen charred benchtops from runaway decomposition. But those water molecules don't stick around forever. Open the cap too many times, or let the environment get too dry, and the hydrate can start creeping toward its more volatile cousin. So, dry, warm air makes the risk climb.
Manufacturers list basic handling precautions for HOBt hydrate, such as keeping it in a cool, dry place, sealing containers tightly, and labeling all bottles. Advice can sound a bit like common sense, but the details matter. Cold storage, such as a refrigerator set at about four degrees Celsius, keeps the hydrate form stable. Desiccators usually seem a safe bet for lab chemicals, but with this material, that can encourage slow water loss over time, pushing it toward greater reactivity. I’ve seen researchers keep HOBt hydrate right next to their standard reagents, out of direct sunlight and away from heat sources. This usually works for a week or two, but long-term storage calls for something more vigilant.
One small step that pays off is writing date-opened notes on every bottle. It’s plain old record-keeping, but it makes it easier to spot older containers before water content drifts out of spec. Old bottles of HOBt hydrate often slip under the radar in large stockrooms. Tossing anything past its prime doesn’t waste much money, but it does trim the chances of an accident.
Spills don’t happen every day, but keeping proper spill kits nearby tells everyone safety isn’t an afterthought. Users should wear eye protection and gloves every time. Sodium bicarbonate or similar agents work for neutralizing spills, and prompt cleanup with damp disposable towels cuts down on dust and airborne risk.
Supply companies have started shipping HOBt hydrate in moisture-proof containers. I get some peace of mind knowing seals have not been tampered with and that incoming shipments include certificates confirming moisture content. Sites that receive bulk shipments need to train staff on transferring powder without exposing it to air for long. Reminders help—leave the bottle open for five minutes, and you’re letting more water slip away than you think.
From experience, keeping hazardous materials in proper storage is not an optional step, especially when working in teaching labs or busy manufacturing spaces. A great storage setup relies on cool temperatures, air-tight containers, date-labeling, and mindful handling. Not only does this legal compliance prevent product waste, but it also could save someone from a nasty surprise.
Chemists work with more than just fancy equipment and white coats. Every day, labs rely on chemicals like 1-Hydroxybenzotriazole Hydrate (usually called HOBt hydrate) for critical tasks, from synthesizing medicine to building specialty plastics. One detail that matters a lot: whether a compound can mix with water without trouble. There’s not much use in wishing a solid would just dissolve — sometimes you find out the hard way that stirring for hours gets you nowhere.
HOBt hydrate is more than a mouthful; it’s used a lot in peptide chemistry to help put amino acids together. This reaction usually depends on how easily HOBt hydrate can move around — which comes down to its solubility. Many suppliers, trusted lab manuals, and chemical databases (like Sigma-Aldrich’s standard sheets and PubChem) all say that the hydrate form does dissolve well in water. If you work in a lab, this is exactly what you hope to see: a powder that disappears without leaving chunks at the bottom of the flask.
I have seen this myself. We’d weigh out HOBt hydrate, add it to a flask of water or buffer, and watch it dissolve without much fuss. No clumps, no gritty residue sticking to the glass. Sometimes, warmer water helps, but even at room temperature, you can get a nice solution if you add a reasonable amount. You won’t get much out of throwing spoonfuls in — there’s a practical upper limit — but for most lab routines, you’re in good shape.
People who don’t work with chemicals every day might shrug at the question. For a chemist or pharmacist, the difference between a soluble compound and a stubborn one can throw a wrench into the whole experiment. HOBt’s solubility matters for making safer reactions; it helps keep things controlled and avoids the risks that come with explosive dry forms of the chemical. If it stayed undissolved, it wouldn’t do its job efficiently and might even gum up a process, leading to wasted time and money.
Safety comes up here, too. The hydrate form of HOBt cuts down on worries about accidental ignition. Unlike the anhydrous version, which carries a higher risk if left sitting out, the hydrate dissolves into water smoothly. You get the benefit of easier storage alongside more predictable reaction conditions.
Focusing on solubility helps labs avoid mistakes and stick to safety protocols. People who measure out HOBt hydrate and watch it dissolve know they’re keeping the process safer. If a lab can’t dissolve a reagent, it slows everything down. I’ve seen entire teams scramble for alternatives when a chemical suddenly proves stubborn or uncooperative — and lost days follow right behind.
Educators and supervisors benefit, too. Detailed safety data sheets, good training, and routine safety checks prevent surprises. Equipment maintenance (like using clean, dry glassware) also plays a part. Labs that follow these steps cut down on chemical waste and boost the odds of getting strong, reproducible results.
If someone ever runs into a batch of HOBt hydrate that doesn’t dissolve, several fixes come to mind. Confirm the product’s label — sometimes a mistaken switch with the anhydrous form can happen. Increasing the solvent’s temperature within safety guidelines often helps. A little stirring or shaking goes a long way. Labs can also explore alternate solvents or adjust concentrations if a specific project hits a snag.
At the end of the day, most who work with HOBt hydrate find its water solubility straightforward, reliable, and crucial for the work they do. This isn’t just convenience — it’s about safety, getting the best results, and not losing precious hours to a problem that shouldn’t exist in the first place.
| Names | |
| Preferred IUPAC name | 1H-1,2,3-Benzotriazol-1-ol monohydrate |
| Other names |
HOBt hydrate 1-Hydroxy-1,2,3-benzotriazole hydrate N-Hydroxybenzotriazole hydrate 1H-Benzotriazole, 1-hydroxy-, hydrate HOAt hydrate |
| Pronunciation | /ˈhaɪdrɒksiˌbɛnzoʊˈtraɪəzoʊl ˈhaɪdreɪt/ |
| Identifiers | |
| CAS Number | 123333-53-9 |
| Beilstein Reference | 3913282 |
| ChEBI | CHEBI:75829 |
| ChEMBL | CHEMBL3315672 |
| ChemSpider | 165350 |
| DrugBank | DB11345 |
| ECHA InfoCard | 03e2fe38-c81e-4969-947d-3ef0f1f8939a |
| EC Number | 202-723-9 |
| Gmelin Reference | 85832 |
| KEGG | C11430 |
| MeSH | D017790 |
| PubChem CID | 70678771 |
| RTECS number | XS8050000 |
| UNII | EC2OO1ZDA6 |
| UN number | UN1325 |
| CompTox Dashboard (EPA) | DTXSID5020185 |
| Properties | |
| Chemical formula | C6H5N3O·xH2O |
| Molar mass | 169.15 g/mol |
| Appearance | White to off-white crystalline powder |
| Odor | Odorless |
| Density | 1.28 g/cm³ |
| Solubility in water | Soluble in water |
| log P | -0.5 |
| Acidity (pKa) | 5.1 |
| Basicity (pKb) | 8.1 (pKb at 25 °C) |
| Magnetic susceptibility (χ) | -51.5e-6 cm³/mol |
| Refractive index (nD) | 1.637 |
| Viscosity | Viscous liquid |
| Dipole moment | 6.2 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 229 J/mol·K |
| Std enthalpy of formation (ΔfH⦵298) | -46.5 kJ/mol |
| Std enthalpy of combustion (ΔcH⦵298) | -230 kJ/mol |
| Hazards | |
| GHS labelling | GHS02, GHS06, GHS08 |
| Pictograms | GHS05,GHS07 |
| Signal word | Warning |
| Hazard statements | H302, H315, H319, H335 |
| Precautionary statements | P280, P261, P301+P312, P305+P351+P338, P337+P313, P330 |
| NFPA 704 (fire diamond) | 1-1-0- |
| Flash point | 54 °C |
| Lethal dose or concentration | LD50 (oral, rat): 640 mg/kg |
| LD50 (median dose) | LD50 (median dose): Oral, rat: 920 mg/kg |
| NIOSH | SN1750000 |
| PEL (Permissible) | No occupational exposure limit (PEL) established. |
| REL (Recommended) | **0.5 mg/m3** |
| IDLH (Immediate danger) | NIOSH: Unknown |
| Related compounds | |
| Related compounds |
Benzotriazole 1-Hydroxybenzotriazole 1,2,3-Benzotriazine 2-(1H-Benzotriazole-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) Oxyma Pure |
