The story of phenolsulfonic acid began in the nineteenth century, shaping the direction of both dye and pharmaceutical industries. Chemists searched for new sulfonation processes, trying to expand phenol’s solubility and reactivity. Through various experiments, researchers discovered that phenol treated with sulfuric acid showed quite transformative results. This reaction gave the world phenolsulfonic acid, which quickly became a critical building block for several synthetic routes. Historical patents and literature from the late 1800s mention early coloring agents, disinfectant blends, and early resin formulations, tying this compound to industrial growth. The need for better, safer disinfectants and more stable synthetic resins during world wars fueled its adoption well before modern chemical plants took over.
At a glance, phenolsulfonic acid appears like a viscous, often golden-brown liquid, ready to corrode the unwary. Its pungent smell hints at strong reactivity, and many in chemical plants remember the stains it leaves behind long after a spill. It typically arrives in drums or carboys, sometimes stabilized by a bit of water, and the labeling calls out a host of synonyms: Benzenesulfonic acid, Hydroxybenzenesulfonic acid, and variants like 2- and 4- isomers. No matter the name, the applications branch out—ranging from resin catalyst to industrial cleaner to dye intermediate. The importance of clear, consistent product labeling stands out the most where operators need to distinguish between similar-sounding but very different sulfonic acids.
Phenolsulfonic acid combines acidity with water solubility and impressive reactivity, especially compared to plain phenol. It doesn’t freeze easily, but when it does, it forms a tough crystalline mass. It chews through metals if left unprotected, and always demands personal protective equipment—Nitrile gloves, coated aprons, and plenty of ventilation. In practice, anyone who has cleaned glassware after a phenolsulfonic acid run knows about its tenacity. Chemically, the introduction of the sulfonic group at ortho or para positions transforms phenol from a simple organic molecule into a forceful acid and an excellent sulfonating agent. The fusion of phenol’s aromatic ring with a sulfonic acid group lets this compound perform in ways neither sulfuric acid nor phenol alone can match.
In the field, you see technical data sheets focusing on parameters such as active acid percentage, water content, and iron content. Chemists pay special attention to assay results, knowing that a small shift can compromise entire reaction processes, especially in resin manufacture or dye synthesis. Quality protocols require clear storage instructions, with warnings about segregating acids from alkalis and temperature swings. The Safety Data Sheet offers up information about proper tanker unloading, neutralization steps for accidental spills, and the need for acid-resistant pumps and hoses. The labels stick hard to regulations, stamping hazard symbols for corrosivity and strong environmental caution. This tight focus on technical specs gives users confidence, knowing exactly how much active component they’re handling and what precautions count most before putting any drops into a batch.
Preparing phenolsulfonic acid is a textbook demonstration of direct sulfonation. Pour phenol into a reaction vessel, heat gently, then add concentrated sulfuric acid. The temperature control makes the difference—too hot and side reactions surge; too cold and sulfonation barely proceeds. Industrial plants often use automated dosing to deliver the acid, followed by holding periods and careful cooling. Waste streams always receive monitoring for residual acidity and organics that might challenge downstream systems. In research settings, small batch runs call for strict fume hood usage and thorough glassware washing. This preparation, far from glamorous, rewards the patient operator with quality product and minimal waste if executed with discipline and plenty of respect for the reactants.
Phenolsulfonic acid participates in a wide variety of reactions, especially those involving further substitutions or condensations. Resin chemists value how it promotes the condensation of formaldehyde with phenol, driving the formation of resoles and novolacs for plywood adhesives and molded components. In sulfonation reactions, its presence as either a catalyst or reactant ensures efficient introduction of sulfonate groups onto aromatic rings. Further modifications through neutralization generate salts like sodium phenolsulfonate, which find use in electroplating cleaner blends and textile dye baths. Reactive sites at the ortho- or para- positions allow researchers to build more elaborate molecules—pharmaceutical intermediates, complex surfactants, or novel corrosion inhibitors. Each reaction calls for a deep understanding of acid strength, temperature control, and careful quenching, skills developed through long hours in the lab and on the factory floor.
Walk through a chemical warehouse and you’ll spot phenolsulfonic acid under several names, depending on supplier and region. The most common are 2-Hydroxybenzenesulfonic acid, 4-Hydroxybenzenesulfonic acid, and sometimes a blend of both isomers. Catalogues list them as Benzenesulfonic acid, phenol-, or as trade blends paired with sodium or potassium salts. Older European literature sometimes uses antiquated labels from early dye chemistry. Exact synonym usage matters, as regulatory filings, shipping labels, and custom duty records demand matching names to prevent confusion or legal issues. In export or multi-site operations, unifying these synonyms and CAS numbers becomes a job of its own for regulatory teams, ensuring that what reaches the reactor is exactly what the chemist ordered—and not something a little too reactive for safety’s sake.
Handling phenolsulfonic acid brings certain risks, and experience on the plant floor drives this home faster than any safety video. Exposure risks include severe skin burns, eye damage, and long-lasting stains on floors and clothing. All facilities require showers and eyewash stations within steps of acid storage banks, and breathing protection is not optional in poorly ventilated spaces. Acid-resistant gloves, face shields, and chemical aprons form the minimum uniform. Management teams drill response procedures, knowing that swift spill neutralization limits both injuries and regulatory fallout. Standard operating procedures highlight the incompatibility with bases and metals, clearly directing all transfer lines and pumps to be checked before any operation. Strict adherence to equipment inspection schedules, leak prevention devices, and clear labeling underpins every safe shift, as lessons learned from near-misses circulate amongst crews to protect every new staff member and old hand alike.
Few other acids cover such a wide range of uses. In the resin and plastics industry, the role as a curing catalyst shapes the durability and strength of outdoor plywood and electrical laminated panels. Water treatment plants inject phenolsulfonic acid-derived products for scaling control and cleaning of reverse osmosis equipment, taking advantage of its reactivity with ions that foul membranes. Dye manufacturers rely on its sulfonic group as an anchoring site, binding colorants permanently to fibers and threads. Disinfectant makers still use it as a raw material, especially in historical blends that combat spores and bacteria. Electroplating operations embrace its salts to scrub metals bright and produce smooth, adherent coatings. The pharmaceutical world uses sulfonated phenols as stepping stones for complex antihypertensive and antimicrobial agents. Each application comes from a blend of historical trial, detailed chemistry, and years of feedback from those who use the finished products every day.
In laboratories and R&D wings, work never stops on improved phenolsulfonic acid solutions or safer production protocols. Recent studies look into reducing corrosivity through more stable salt formation, or finding greener sulfonation routes using alternative acids or recyclable catalysts. Polymer chemists branch into novel resin-hardening technologies, aiming for adhesives that release fewer toxic byproducts and boast longer shelf lives. Analytical chemists test for trace impurities, developing advanced chromatographic methods to monitor batch quality in real time. Formulation scientists focus on blending phenolsulfonic acid with performance boosters for water treatment and cleaning markets, responding to rising regulatory hurdles on effluent discharge. Across the world, consortiums pool patents and process improvements, pushing the field towards tighter controls, more energy-efficient operations, and smarter, safer chemical handling.
Health researchers dug into phenolsulfonic acid’s toxicity profile, realizing early on the need for solid data to back up safe exposure limits. Animal studies found oral and dermal routes could cause tissue corrosion and systemic toxicity at higher exposure levels, but with predictable dose-response relationships. Chronic exposure links to respiratory distress and potential systemic effects, prompting calls for stricter indoor air limits. Wastewater studies highlight the risk of aquatic toxicity, where improper discharges harm fish, invertebrates, and disrupt aquatic microbiomes. Regulatory agencies draw on this data to set occupational exposure limits and demand robust spill containment infrastructure. At the industrial user level, the drive is to tighten up transfer protocols and improve process containment so that risk to both staff and the environment drops with every improved system.
Looking ahead, phenolsulfonic acid continues to evolve in technology, regulation, and user expectation. As manufacturing standards tighten worldwide and environmental compliance costs rise, research pours into less toxic, more easily neutralized analogues and recycling methods for spent solutions. Bio-based phenol sources are under active development, promising a path away from traditional petroleum feedstocks. Water treatment sectors look for more selective derivatives, ones that tackle emerging contaminants and resist biological fouling. Growing scrutiny over chemical plant emissions forces producers to update procedures, and digital monitoring arrives in tank farms and control rooms. Each new shift in the industry brings another round of process tweaks and product audits, yet the basic chemical remains, underlining its place in modern industry. The drive towards safer, cleaner, and more responsible chemical stewardship remains constant, echoing through every lab and plant floor reliant on phenolsulfonic acid’s unique capabilities.
Phenolsulfonic acid lands on lab benches across the world mainly because of its sharp ability to break things down and make new bonds happen. Synthesizing resins and plastics often asks for serious catalysts, and phenolsulfonic acid fits right in. Its strong acidic properties do the heavy lifting, helping companies craft phenolic resins with a solid backbone that stands up to everything from heat to moisture. It’s not a household name, yet the adhesives holding furniture or brake pads owe a lot to the power packed in this chemical.
Cleaning industrial equipment can turn into a chore, especially when metals are involved. Deposits of scale and tough residues build up over time. Phenolsulfonic acid comes to the rescue as a descaler in metal treatments and cleaning solutions. During my time assisting in a manufacturing plant, I saw workers reach for bottles of it when pipes started losing efficiency due to buildup. A flush with this solution clears up problems fast, and equipment gets back on line sooner, avoiding expensive repairs or downtime.
Chemists count on phenolsulfonic acid during organic synthesis. Its role as a sulfonating agent gives plenty of research avenues—sometimes it’s the invisible hand that shapes the pathway for creating medicinal compounds, dyes, and other distinct chemicals. During my postgraduate research, our team leaned on it to tweak molecules for better pharmaceutical results. There’s something about being able to steer a reaction in the lab with just a few drops from a flask that makes the process feel like controlled magic.
Paper mills, textile producers, and other industries find a trusted helper in phenolsulfonic acid. Dyes stick better and colors pop brighter due to its role in the dyeing process. Textile factories have reported smoother dye application after integrating this solution. The chemical transforms cellulose fibers to accept color more willingly, giving clothes their sharp appearance straight from the rolling machines.
While the solution packs a punch with its benefits, handling it without respect brings hazards. Workers need proper gloves and eye protection; a spill on skin burns quickly. In factories I’ve visited, signs and stations for emergency washing underline how important it is to treat the chemical with care. Regulatory agencies worldwide urge responsible storage, as spills harm both workers and the environment.
New research points toward greener acids and catalysts, aiming for similar results without as many risks. Some companies have started phasing in milder chemicals but phenolsulfonic acid's affordability and effectiveness slow the transition. If regulators set tighter limits, safer alternatives may finally catch up.
Phenolsulfonic acid quietly supports modern manufacturing, research, and even textile colors many people enjoy. The lesson? Even chemicals out of the public eye shape industries and daily life in ways most folks never notice. Using them responsibly and exploring better options will make sure their benefits keep rolling in safely.
Phenolsulfonic acid doesn’t mess around. It’s a strong acid, tough on skin, harsh on eyes, and a real problem for lungs if the fumes drift your way. The smell alone reminds you to stay alert. Folks who work in labs or factories quickly learn to respect this chemical—not just for its uses, but for the harm it’ll cause if handled wrong. Stories from industrial settings land hard. Splashes burn deep and the fumes scratch at your throat, setting off coughs you don’t forget. Working safely with phenolsulfonic acid feels less like a suggestion, more like a strict rule everyone has to follow for their own good.
Regular cotton shirts or thin gloves won’t cut it. It’s full-coverage, chemical-resistant gloves—like nitrile or neoprene—that keep acid off your hands. People often double up if they’ve seen the scars left by a careless spill. Goggles get swapped for full-face shields where splatter can happen. Tyvek suits or chemical aprons guard against stray droplets. Sturdy, closed shoes matter, and you don’t want to learn that lesson the hard way. One mistake, and you’re remembering the sting for weeks.
You need fresh air. Whether it’s a fume hood in a lab or strong exhaust fans on a factory line, those setups don’t just clear the air—they keep your lungs from taking the hit. Back in college, anyone opening these bottles under a bench without a hood paid for it with days of coughing. Grab a respirator if fumes get thick or if you’re working with big batches. Many overlook that step, up until the burning starts.
Phenolsulfonic acid needs a real container—HDPE or glass with tight lids, zero cracks, and no mystery labels. One coworker once left a barely sealed jug on a shelf, and the fumes turned into a headache for the whole room by lunch. Keep it away from heat and sunlight, far from any bases or organics that could react. Spills have to get cleaned up right away—absorbent pads, plenty of water for dilution if the surface allows, and staff who know what to do without panicking. Acid burn kits and showers nearby aren’t optional.
No one just hands you a bottle of this stuff if you’re the new guy. It’s hands-on lessons, full walkthroughs, and spot checks until you handle things right. A rushed new worker once got to spend an afternoon with HR after skipping glove checks. Supervisors repeat the same line: “Don’t guess—if you don’t know, ask.” That attitude keeps everyone safer. Training should include what to do in a fire, too. Water won’t always work—special extinguishers matter. Cuts on the hands or open wounds mean you should step aside and let someone else take over.
It’s the little habits that stop most accidents. Label everything clearly. Make sure the emergency shower works before you ever need it. Don’t eat, drink, or use your phone near acid containers. Wash your hands, even if you wore gloves. Speak up if someone gets careless. These rules didn’t pop up from nowhere—they came from real injuries and close calls. You protect yourself, and the next shift, by leaving things tidy and safe.
Companies that cut corners on training or gear invite trouble. Places that run regular refreshers, invest in protective gear, and follow up on small mistakes create a safer working environment. Open communication, clear signage, and steady investment in good facilities make steady, real-world progress. It isn’t about paranoia, just smart habits built from experience. That’s what keeps accidents rare, and everyone heading home in one piece.
Phenolsulfonic acid shows up often in industrial cleaning, resin production, and laboratory settings. Unlike more familiar household acids, this substance brings both brute force and a temper. I remember the first week at my old chemical plant job – a leak in the storage room turned my gloves gummy and ruined a set of boots in a few minutes. That lesson sticks: storing harsh chemicals sloppily invites trouble.
You won’t find phenolsulfonic acid in glass Mason jars or rusty cans. Experts and regulators recommend high-density polyethylene (HDPE), PTFE, or other plastics proven to resist the acid’s aggressive nature. Even the best stainless steel can corrode from prolonged contact. I’ve seen maintenance teams scramble when someone unknowingly stored an acid drum on an unprotected metal rack, leaving behind streaks of orange-brown corrosion a week later.
Heat speeds up reactions and can trigger hazardous fumes from phenolsulfonic acid. Storage areas lacking temperature control often turn into slow-moving disasters. Any sunlit area or hot warehouse corner raises risks. Storing the chemical between 15 to 25°C (59 to 77°F) avoids most seasonal swings, and steady ventilation helps keep humidity down. I’ve seen drums sweep up moisture from the floor overnight in humid climates, leaving surfaces unexpectedly slippery.
Phenolsulfonic acid does not get along with alkalines, oxidizers, or cyanides. Mixing by accident leads straight to toxic gas or runaway heat. Storing it behind a simple physical barrier works wonders. I once witnessed a shelf-labelling mix-up trigger an expensive evacuation—someone stacked bleach three feet away from an acid spill zone. Double-check storage signs and keep reactive chemicals clearly separated.
Early in my career, newcomers used to wander into chemical storage with casual sneakers and open cups of coffee. After one brief acid splash landed on exposed skin, the attitude changed fast. Good facilities demand thick gloves, splash goggles, and long sleeves as the bare minimum. Quick-access eyewash stations nearby have saved more than one person from a rough day.
No container lasts forever—leaks, label damage, and human mistakes creep in. Clear up-to-date records help responders track what’s stored where, no guessing required. At my last job, a routine sticker check revealed three bottles missing hazard tags after half a year, so cross-checking inventory with supply logs makes a difference. Safety sheets, spill kits, and training sessions cut down panic during incidents.
Dumping old phenolsulfonic acid cuts corners and pollutes, risking fines and long-term harm. Proper waste handling means connecting with certified hazardous material handlers and relying on tested neutralization procedures. Many local laws set strict disposal rules, which come with hefty penalties if ignored.
Careless handling of chemicals still causes injuries and environmental problems. Proper storage isn’t just a rulebook obligation—it's a matter of keeping coworkers safe, limiting financial losses, and protecting the wider community. Diligence builds trust between management, workers, and regulators alike.
Anyone who has ever poked around in a chemistry lab or dived into the manufacture of industrial chemicals will recognize phenolsulfonic acid as a pretty common ingredient. The basic formula, C6H6O4S, puts it in the family of organic sulfonic acids formed by sulfonation of phenol. Most often, you find it in either the 2- or 4-position isomer, thanks to how phenol reacts with sulfuric acid. You pour concentrated sulfuric acid over phenol, and it gives deep orange or reddish crystals that dissolve nicely in water.
From a practical point of view, phenolsulfonic acid solutions usually fall in a range between 65% and 75% by weight. That means the rest is mostly water, though you get trace leftovers from the manufacturing process, like free sulfuric acid—sometimes up to 3%. The pH drops off the deep end, sitting close to zero, so this liquid stays pretty aggressive.
Lab settings and industry rely on accurate titration to check just how much phenolsulfonic acid sits in the batch. I spent a summer internship tracking this stuff with indicators and titrators; accurate concentrations mattered because too much unreacted sulfuric acid changes how the chemical interacts with resins or dyes.
I’ve run into production managers losing patience because weak solutions make processes drag or fail completely. In ion exchange resin production, for example, the wrong concentration affects consistency. Go too strong, and the batch doesn’t cure right. Go too weak, and it never reaches the finish line. Some manufacturers track key numbers, like 70% phenolsulfonic acid, since it works best for sulfonation reactions without corroding storage tanks too fast.
Lab suppliers sometimes offer technical-grade solution at 65%, while specialty applications—such as analytical chemistry—demand tighter specs and purities. It’s always a give and take: higher concentration means higher reactivity, but also a bigger risk of overflow or spattering during mixing. Chemical reactions just respond better to consistency.
Anyone handling phenolsulfonic acid solution quickly learns about corrosion and the need for proper safety equipment. Gloves and goggles keep hands and eyes out of harm’s way, and storing the acid in PTFE or glass bottles reduces the risk of tank leaks or unexpected reactions. The fumes alone can be tough, especially above 70% strength. I’ve seen new lab techs make the mistake of leaving a bottle open, only to find nearby metals rusting within hours.
In production, it’s smart to monitor concentration with regular sampling, especially if the solution sits for a long time or faces temperature swings. Water can evaporate, concentrating the acid. I’ve had to recalibrate a batch after a hot day raised the concentration above target—worth the hassle to avoid ruined product and wasted resources. Periodic checks with refractometers or auto-titrators curb most of these surprises.
Manufacturers can do a lot to prevent mismatches in concentration. Rigorous quality control, batch tracking, and standardizing supplier specs support more reliable results, whether in lab research or industrial-scale applications. Factories that don’t keep an eye on concentration end up with fouled machines or inconsistent products, which costs money and trust.
Phenolsulfonic acid stands as a mainstay for many processes, but only if its concentration and purity are kept in check. From small-batch testing to the demands of mass production, the details shape both safety and quality. Strict habits and solid equipment make a measurable difference, especially when things heat up and production speeds climb.
Phenolsulfonic acid packs a punch. This stuff burns through skin, metal, and a lot of lab equipment. Pouring it down the drain seems easy, but it corrodes pipes and can pollute water sources. Growing up around folks in the trades, I picked up a healthy respect for what goes into the ground or down the sink. Every drop makes an impact somewhere down the line—often in places we never see.
Most people never think about chemicals after they disappear. Out of sight, out of mind, as they say. But dealing with acids, especially ones like phenolsulfonic acid, calls for more than wishful thinking. This material can cause real harm to people, wildlife, and the environment if tossed carelessly. My background in environmental science taught me to look past the label and think about the aftermath.
Sulfonic acids do not break down easily; they stick around and interact with whatever they touch. That starts with plumbing, then reaches wastewater treatment plants. These facilities handle regular sewage, not hazardous waste. Throwing strong acids into that mix can endanger workers, damage expensive treatment gear, and let contaminants slip through into rivers or groundwater.
Regulations exist for a reason. The U.S. Environmental Protection Agency, for example, sets strict waste disposal guidelines. Breaking rules brings big fines, but the real damage often gets paid out later: sick workers, ruined habitats, lost trust.
Chemical safety has no shortcuts. Start with a label and Safety Data Sheet (SDS). That document sets out risks and spells out compliant disposal methods. Each batch of phenolsulfonic acid should get stored in a clearly marked, corrosion-resistant container. Trying to transfer something so sticky and aggressive without the right gear is a quick way to get hurt.
A hazardous waste service often provides the best route. Licensed companies pick up chemicals and handle the neutralization, transportation, and final treatment. I’ve seen labs store old containers for years, hoping nobody notices; those situations turn into leaks and emergencies later. Regular pickups cut down that risk and keep people honest.
Some chemical waste can be neutralized before disposal, but phenolsulfonic acid makes this tricky. Mixing acid with just any base leads to heat, fumes, or even explosions. Anyone without training should leave this part to professionals. If neutralization fits the regulations and the SDS agrees, it should always take place in a fume hood, with spill kits and personal protective gear at the ready.
Safe chemical disposal doesn’t fall on one person. Labs, factories, and schools need to teach every staff member the right process. Posters, reminders, and checklists go a long way to cut mistakes. Good habits can form from training, clear rules, and reliable support from waste management professionals.
I’ve visited places where corners got cut on chemical safety. It always catches up with people. Accidents bring injury, cost time, and sometimes ruin communities. Proper chemical handling and disposal cost money and effort, but the peace of mind lasts much longer.
Protecting our water, land, and air from harm isn’t just about following rules—it’s about clean living. Each person who learns the ropes and pushes for safer handling of harsh chemicals adds a layer of protection for the next generation. That’s an investment worth making, every time.
| Names | |
| Preferred IUPAC name | 4-hydroxybenzenesulfonic acid |
| Other names |
Benzenesulfonic acid Phenol-4-sulfonic acid Sulfonic acid, phenyl- 4-Hydroxybenzenesulfonic acid |
| Pronunciation | /ˌfiː.nɒlˌsʌlˈfɒn.ɪk ˈæs.ɪd/ |
| Identifiers | |
| CAS Number | 98-67-9 |
| Beilstein Reference | 1209227 |
| ChEBI | CHEBI:31201 |
| ChEMBL | CHEMBL1563329 |
| ChemSpider | 15917 |
| DrugBank | DB14656 |
| ECHA InfoCard | 100.012.851 |
| EC Number | 215-465-3 |
| Gmelin Reference | 604332 |
| KEGG | C00623 |
| MeSH | D010649 |
| PubChem CID | 61253 |
| RTECS number | SN6475000 |
| UNII | K0X367FGL7 |
| UN number | UN2585 |
| CompTox Dashboard (EPA) | DTXSID0028591 |
| Properties | |
| Chemical formula | C6H6O4S |
| Molar mass | 172.18 g/mol |
| Appearance | Clear brown liquid |
| Odor | Pungent |
| Density | 1.245 g/cm³ |
| Solubility in water | soluble |
| log P | -2.3 |
| Vapor pressure | Negligible |
| Acidity (pKa) | -2.8 |
| Basicity (pKb) | 5.92 |
| Magnetic susceptibility (χ) | -5.2e-6 |
| Refractive index (nD) | 1.572 |
| Viscosity | 20-30 cP (at 25°C) |
| Dipole moment | 7.6 D |
| Thermochemistry | |
| Std molar entropy (S⦵298) | 223.0 J·mol⁻¹·K⁻¹ |
| Std enthalpy of combustion (ΔcH⦵298) | -1440 kJ/mol |
| Pharmacology | |
| ATC code | R05CB12 |
| Hazards | |
| Main hazards | Corrosive, causes severe skin burns and eye damage, harmful if swallowed or inhaled, may cause respiratory irritation. |
| GHS labelling | GHS05, GHS06 |
| Pictograms | GHS05 |
| Signal word | Danger |
| Hazard statements | H314: Causes severe skin burns and eye damage. |
| Precautionary statements | P260, P264, P280, P301+P330+P331, P303+P361+P353, P305+P351+P338, P310, P405, P501 |
| NFPA 704 (fire diamond) | 3-0-2-Acid |
| Flash point | 138°C |
| Autoignition temperature | 220°C (428°F) |
| Lethal dose or concentration | LD50 oral rat 2470 mg/kg |
| LD50 (median dose) | LD50 (median dose): Oral rat LD50 = 400 mg/kg |
| NIOSH | SN4175000 |
| PEL (Permissible) | 5 ppm (mg/m3) |
| REL (Recommended) | 100% |
| IDLH (Immediate danger) | 250 ppm |
| Related compounds | |
| Related compounds |
Benzenesulfonic acid p-Toluenesulfonic acid Sulfanilic acid Phenol Sulfuric acid |
