2B Acid
2B Acid — also known as CLT Acid, Red 2B Acid or Brilliant Toning Red Amine — is the workhorse diazo component behind one of the most widely produced families of azo pigments: the Pigment Red 48 / Pigment Red 2B "toner red" series used across printing inks, plastics masterbatch, paints and rubber colouration.
Chelora Chemicals supplies 2B Acid to pigment manufacturers, ink formulators and dye houses worldwide, in bags and drums, with a batch COA and GHS safety data sheet on every consignment.
Product identity
- CAS Number
- 88-51-7
- IUPAC name
- 2-Amino-4-chloro-5-methylbenzenesulfonic acid
- Molecular formula
- C7H8ClNO3S
- Molecular weight
- 221.66 g/mol
- EC / EINECS
- 201-837-6
- MDL number
- MFCD00035771
- SMILES
- Cc1cc(N)c(cc1Cl)S(=O)(=O)O
- HS Code
- 2921.43*
* Confirm the exact HS heading with your customs broker — classification of amino-sulfonic acid dye intermediates can vary between destination tariffs.
What 2B Acid is used for
2B Acid is an aminobenzenesulfonic acid carrying a chlorine and a methyl group positioned to give a stable, easily diazotised amine. That combination does a lot of work: the amine diazotises cleanly, the sulfonic acid group carries the molecule as a water-soluble sodium salt right up to the coupling step, and the chloro-methyl substitution pattern on the finished pigment gives the deep red shade, bleed resistance and heat stability that make the Pigment Red 48 / Red 2B family a standard choice across the ink and plastics industry.
In practice 2B Acid is a captive intermediate: pigment plants buy it to diazotise and couple onto naphthol components in-house. Very little of it is ever resold as-is once converted.
Why the exact isomer and salt form matter
Sulfonic-acid dye intermediates are not interchangeable, and a substitution downstream is not recoverable:
- 2B Acid (CAS 88-51-7) — this product. Also known as CLT Acid, Red 2B Acid or Brilliant Toning Red Amine; the standard diazo component for the Pigment Red 48 series.
- 4B Acid and related chlorotoluidine-sulfonic acid isomers — closely related regiochemistry with different chlorine/methyl/amine positioning, giving different coupling behaviour and shade. We supply these alongside 2B Acid — see our pigment intermediate range.
- Free acid vs. sodium / ammonium salt — the free acid is essentially insoluble in water; the sodium or ammonium salt is the form actually diazotised in most plants. Confirm which form your process is set up for before ordering.
If your purchase order simply says "2B Acid" or "CLT Acid", tell us the pigment or dye you are producing and we will confirm the correct isomer, purity grade and salt form before the order is placed.
Appearance and handling character
2B Acid ships as a white to pale red or buff crystalline powder that does not show a clean melting point — like most aromatic sulfonic acids it decomposes on strong heating rather than melting, typically above 300 °C. As the free acid it is essentially insoluble in cold water, which is exactly why the sodium or ammonium salt form is what most plants actually charge to their diazotisation vessel. Like other aromatic amines it can show mild colour drift on prolonged exposure to air and light, which is cosmetic in most routes but worth avoiding wherever shade consistency is critical. Read the next section before planning any handling: the material carries skin and eye irritation hazards, and that should shape your controls from the outset.
| Parameter | Typical value |
|---|---|
| Appearance | White to pale red / buff powder |
| Assay (titration, sodium-salt basis) | 98.0% min |
| Moisture | 1.0% max |
| Free amine (unreacted) | Reported per batch |
| Sulfate ash | Reported per batch |
| Colour value (shade) | Matched to reference standard on request |
Important: the figures above are indicative of commercial grade material and are offered for planning only. The batch certificate of analysis is the governing document. If your process demands a tighter assay, a specific colour-value match to your existing pigment standard, or a controlled moisture figure, send us the specification and we will quote against it rather than against a generic grade.
| Property | Value |
|---|---|
| Physical state | Crystalline powder at ambient |
| Decomposition point | > 300 °C (does not clean-melt) |
| Relative density | ≈ 1.30 (estimate) |
| Water solubility (free acid) | Essentially insoluble |
| Water solubility (Na / NH₄ salt) | Freely soluble |
| Solubility, organic solvents | Slightly soluble in DMSO; largely insoluble elsewhere |
| Oral LD₅₀ (rat) | ≈ 12,300 mg/kg — low acute oral toxicity |
| Odour | Faint, characteristic |
Physical constants compiled from public reference data for CAS 88-51-7 and rounded for readability. Treat them as orientation, not as a specification.
Where our customers put this molecule to work
2B Acid is a focused intermediate: its volume is concentrated in azo pigment manufacture, with smaller outlets in dye chemistry and specialty organic synthesis.
Pigment Red 48 / Red 2B series
The primary outlet. Diazotised 2B Acid is coupled onto beta-naphthol type coupling components to build the calcium, barium and manganese "toner red" lakes used across printing inks, PVC and plastics colouration.
- Diazo component for red toner pigments
- Isomer purity shows up directly as off-shade
- See also our naphthol coupling components
Printing ink & plastics masterbatch
Pigment Red 48 lakes made from 2B Acid are prized in packaging inks and plastics masterbatch for their brightness, bleed resistance and cost-effective strength compared to organic reds requiring more complex synthesis.
- Flexo and gravure ink formulation
- PVC, PE and PP masterbatch colouration
- Heat-stable across common processing ranges
Paint & rubber colouration
The same lake pigments extend into decorative and industrial paints, and into rubber compounding, wherever a bright, reasonably lightfast red is needed at a lower cost point than a high-performance organic pigment.
- Emulsion and solvent-based paint tinting
- Rubber and elastomer colour masterbatch
- Specified against a shade card, not by CAS alone
Textile & leather dye chemistry
A secondary outlet: the same diazotisation chemistry that builds the pigment lakes also feeds smaller-volume azo dyes used in textile and leather colouration where the chloro-methyl shade profile is wanted.
- Azo dye synthesis for textile substrates
- Leather finish colourant chemistry
- Available in trial and laboratory quantities
Fine & specialty synthesis
A well-characterised aryl amine building block for custom sulfonamide, amide and heterocyclic chemistry where the specific chloro-methyl-sulfonic acid substitution pattern is required.
- Custom amide and sulfonamide formation
- Building block for specialty organics
- Available in small research quantities
Contract & scheduled supply
Pigment plants run to production campaign, not to a calendar month. Most 2B Acid buyers want tonnage released against a manufacturing plan rather than in one shipment. We hold inventory and release it to your schedule.
- Annual contracts with scheduled call-off
- Price held across the contract period
- Second source held in reserve
How we supply 2B Acid
Chelora Chemicals is a supplier and sourcing partner, not a manufacturer. We own no pigment-intermediate plant — and for a shade-sensitive product like this one, that independence works in your favour. We are never obliged to push you whatever a captive unit happens to be running that month.
Instead we place your order with whichever qualified producer best matches your assay, your colour-value requirement, your price point and your delivery window.
We keep a second qualified source on this line. When a plant goes down for maintenance, or a monsoon disrupts a road corridor, your campaign switches source rather than stalling.
- Specification read against the CAS and salt form first. We confirm you need 88-51-7 as the sodium or ammonium salt, not the free acid or a related isomer, before we quote a price.
- Batch COA shared before dispatch. You approve the assay, moisture and colour-value profile against your own spec while the material is still in our warehouse.
- Hazard status stated up front. We flag the skin and eye irritation classification at enquiry stage — not in the small print of a document pack that arrives with the goods.
- Pre-shipment samples for qualification. New account or new source, your R&D team runs a lab-scale diazotisation and coupling trial before the full quantity ever moves.
- Shade consistency tracked batch to batch. Where colour value matters, we hold the reference standard on file and flag any drift before it reaches your production line.
- Export machinery handled in-house. Hazard classification, packing, labelling, freight booking and customs paperwork are ours to manage.
- Consolidation onto one bill of lading. Ship 2B Acid alongside other pigment intermediates from our range — one invoice, one shipment, one counterparty.
Packed the way your plant receives it
Pack format drives your landed cost and your handling effort. Tell us how it will be charged at your end and we will quote the format that suits your operation.
Multi-wall paper & PE bags
Laminated multi-wall bags with an inner liner, palletised and shrink-wrapped. The default for LCL movements and for plants charging batch-wise by hand.
Fibre & HDPE drums
UN-certified drums with liner for longer sea transits and humid destinations. Better protection against moisture pick-up and colour drift than bagged material.
Jumbo / FIBC bags
Bulk bags with liner for high-volume pigment producers with mechanical charging. Fewer handling movements and materially lower packing cost per kilo.
Samples & trial packs
Laboratory samples and pilot quantities dispatched by courier so your R&D team can run a shade trial before committing to campaign volume.
Incoterms to suit you
Quoted on the Incoterm your purchasing team works to. Ocean, air and road freight arranged end-to-end with documentation filed before booking.
Campaign despatch
Pigment production runs to campaign. We hold contracted tonnage and release it against your production calendar instead of landing it all at once.
Handle this as a skin & eye irritant
2B Acid has a favourable acute toxicity profile compared to many dye and pigment intermediates — its oral LD₅₀ in rats is high, indicating low acute oral toxicity — but it is still classified for skin and eye irritation, and it is handled at industrial scale as an aromatic amine derivative. The summary below is orientation only — the safety data sheet supplied with your consignment is the authoritative document and should govern your risk assessment, PPE selection and emergency planning.
Classified hazards
H315Causes skin irritation.H319Causes serious eye irritation.
Hazard statements reflect the harmonised GHS classification commonly published for CAS 88-51-7 and closely related chlorotoluidine-sulfonic acid isomers. Supplier classifications may differ in detail; always read the SDS issued with your specific batch, and treat the irritation entries as the ones that shape your controls.
Spill & emergency orientation
Plan your response before the pallet arrives, not after a bag splits. The points below are orientation for your emergency planners — sections 4, 5 and 6 of the SDS are the authoritative instructions and should be posted at the point of use.
- Sweep, do not hose. Collect spilled solid mechanically into a labelled container; avoid unnecessary discharge of a coloured or diazotisable substance to a drain.
- Suppress dust. Dry sweeping of a fine powder generates an inhalable aerosol — use vacuum collection or dampen carefully in line with the SDS.
- Wash promptly on skin or eye contact. Flush with plenty of water for several minutes and seek medical advice if irritation persists.
- Have the SDS on hand. Any treating clinician should have the product identity and CAS number available for reference.
- Record repeated or significant exposures per your site's occupational health policy, as you would for any classified skin or eye irritant handled at scale.
Storage
- Cool, dry, well-ventilated store, away from direct sunlight and heat sources. The material does not melt in the ordinary sense, but prolonged heat can drive slow decomposition and colour drift.
- Keep containers tightly closed. Air and moisture pick-up can affect the free-flow behaviour of the powder and, over long storage, its shade consistency.
- Segregate from strong oxidising agents and from strong bases if you are storing the free acid form, since reactivity and solubility both change with pH.
- Keep batches separated by lot where colour-value consistency matters — do not blend drums from different production runs without re-checking shade against your standard.
- Shelf life is typically 24 months in sealed original packing under these conditions. Re-assay and re-check colour value before use after long storage.
Handling & PPE
- Standard good chemical hygiene practice applies: avoid generating dust, and use local exhaust ventilation or mechanical charging wherever practical.
- Skin protection. Chemical-resistant gloves and coveralls are recommended given the confirmed skin irritation classification, particularly for repeat handlers.
- Eye protection is required. H319 applies; use chemical splash goggles wherever the powder is handled in the open, especially during charging and sampling.
- Respiratory protection where dust may be generated during bag emptying or drum charging, per your own exposure assessment.
- Wash hands and exposed skin before eating, drinking or smoking, and launder contaminated clothing separately from other laundry.
Transport
2B Acid commonly moves under hazard class 8 (corrosive/irritant category for transport purposes), Packing Group III, though the exact classification can vary by carrier and destination. We classify each consignment, apply appropriate packaging and labelling, and file the necessary declaration before the booking is made. The applicable classification is stated on your shipping documents and SDS — ask us for the current transport paperwork when you plan the shipment.
What travels with every consignment
A chemical shipment is only as good as the file that travels with it. Verifying what the source plant sends is precisely the work you are buying from a supplier.
Certificate of Analysis
Batch-specific assay by titration, moisture, colour value and appearance — checked against your purchase specification before we release the goods.
GHS Safety Data Sheet
Full 16-section SDS in GHS format covering hazards, exposure controls, handling, storage, spill response, toxicology and disposal — issued in the language your destination requires.
Shade / colour-value reference
Where colour value matters to your process, a comparison against an agreed reference standard is provided alongside the standard analytical COA.
Certificate of Origin
Chamber-attested where required, plus preferential-origin forms where a trade agreement gives your import duty relief at the destination.
Third-party inspection
SGS, Intertek or Bureau Veritas sampling and inspection arranged on request before loading, giving you independent verification of what actually ships.
Retained & pre-shipment samples
Pre-shipment samples carry the same COA as the commercial lot, so what your laboratory qualifies is exactly what arrives. Retention samples held against the batch.
From a sulfonic acid amine to a finished red pigment
Everything made with 2B Acid runs through the same two-step logic: diazotise the amine, then couple the diazonium salt onto a naphthol partner. Understanding that sequence explains why the specification matters and which impurity will hurt you. The routes below are the general industrial pattern, not a process disclosure.
Start with the amine
2B Acid provides a primary aromatic amine carrying a chlorine, a methyl group and a sulfonic acid, all positioned to give a stable, well-behaved diazonium salt.
Diazotise
Sodium nitrite in acid at low temperature converts the amine into its diazonium salt — a short-lived, highly reactive species generated and consumed in the same vessel.
Couple onto naphthol
The diazonium salt is coupled onto a beta-naphthol type component to form the azo dye, which is then precipitated as a calcium, barium or manganese lake pigment.
Finish to grade
The crude lake is filtered, washed and dried, then finished to the particle size, strength and shade the end market demands — ink, plastics or paint specification.
Why amine purity carries through the whole route
Both the diazotisation and coupling steps act directly on this one molecule. Anything in the feed that competes with it, or that carries its own reactive functionality, follows the material down the line:
- Isomeric amines diazotise and couple in parallel and give structurally similar azo products — an off-shade or dull pigment that fails a colour-match spec.
- Residual free amine or unreacted intermediate from the sulfonation step can carry through to the diazotisation, wasting reagent and generating side products.
- Oxidation products — coloured species from prolonged air exposure — dull a finished shade and can show as off-colour in an otherwise pale powder.
- Metal and sulfate residues from the manufacturing route concentrate in the lake pigment and can affect brightness, heat stability or regulatory compliance for food-contact and toy-safety applications.
That chain of consequences is the reason we quote against your written specification rather than a generic "technical grade", and the reason the batch COA and, where relevant, a shade comparison are shared for approval before dispatch rather than sent with the invoice.
| Intermediate | Principal outlet |
|---|---|
| 2B Acid / CLT Acid CAS 88-51-7 — this product | Pigment Red 48 series Toner reds for inks & plastics |
| 4B Acid Related chlorotoluidine-sulfonic acid isomer | Related toner red shades Dye intermediate chemistry |
| Naphthol AS / Beta Naphthol | Coupling component Used together with 2B Acid |
If your route calls for a related coupling component or isomer, we supply those as well — see our pigment intermediate range. Send the CAS number and we will confirm the correct material before quoting.
What actually moves the price of this intermediate
2B Acid is not a commodity with a screen price. Knowing what drives the quote helps you time a purchase and read whether an offer is realistic.
Ink & packaging demand cycles
Printing ink and plastics masterbatch demand for toner reds tracks packaging and consumer-goods production, giving the market a fairly steady but seasonally uneven pull.
- Quote early for campaign tonnage
- Spot buying at peak costs materially more
- Contracted call-off smooths the exposure
Upstream feedstock
The route back to 2B Acid runs through toluidine and sulfonation chemistry. Movements in toluene, chlorine and sulfuric acid feed through to the intermediate within a quarter or so.
- Toluidine and sulfuric acid set the floor
- Energy cost weighs on the sulfonation step
- We flag feedstock-driven moves in the quote
Regulatory pressure on azo pigments
Some jurisdictions restrict certain azo colourants in food-contact, toy and textile applications. That compliance burden sits inside the price of the finished pigment and shapes which markets a given grade can serve.
- End-use restrictions vary by jurisdiction
- Heavy-metal limits tighten for consumer goods
- We check destination rules before quoting
Pack format
Cost per kilo falls from 25 kg bags to drums to jumbo bags for high-volume pigment producers running continuous diazotisation lines.
- Small bags carry the highest packing cost
- FIBC is cheapest per kilo at volume
- Drums protect shade-critical batches on long transits
Freight & Incoterm
Ocean freight and destination Incoterm move landed cost as much as the ex-works price does — always compare offers on a like-for-like landed basis.
- Compare on landed cost, not ex-works
- Space books out ahead of peak shipping season
- We quote FOB, CIF, CFR or DDP as you prefer
Source availability
A plant turnaround, an environmental inspection or a monsoon disruption can take capacity offline at short notice. Single-sourced buyers feel this hardest.
- We hold a second qualified source on this line
- Qualify the alternate before you need it
- Ask us about dual-source contracts
| If your end use is… | Specify |
|---|---|
| Printing ink pigments | Tight shade-value match, low metal residues |
| Plastics masterbatch | High assay, controlled heat-stability profile |
| Paint & coatings | Shade consistency, low free-amine residue |
| Textile / leather dyes | High assay sodium salt, tight isomer limit |
| Laboratory / R&D | Small pack, high purity, full analytical pack |
Not sure which column you are in? Describe the pigment or dye you are producing and our technical desk will recommend the grade — including telling you when a cheaper specification would do the job just as well.
Support that goes beyond shipping the bag
What our technical desk will do
- Match a grade to your pigment target. Tell us the shade and application you are running and we will recommend the specification — and say so plainly when a tighter, costlier grade would add nothing.
- Be straight about the hazard profile. We state the skin and eye irritation classification at enquiry stage so your EHS team can plan the controls into the decision, rather than meeting it for the first time on the label.
- Advise on handling and storage for your site conditions, including how to protect shade-critical batches from colour drift in transit.
- Review your specification before it goes into a contract, so you are not locked into a limit that no plant can consistently hit.
Regulatory & compliance notes
- Azo colourant restrictions are application-specific. Several regimes restrict certain azo dyes and pigments in food-contact, toy and children's-product applications. Confirm what applies to your finished pigment's end use.
- Import controls vary by destination. Some jurisdictions apply registration or declaration requirements to dye and pigment intermediates. We check the destination rules before quoting, not after you have raised the PO.
- Chemical inventory listings differ between regions. Confirm your obligations under the applicable inventory regime for your import volume — we will supply the identity data you need for that filing.
- Heavy-metal limits for finished pigments used in consumer goods are increasingly strict. Your regulatory team should confirm the finished-article position for the end use you have in mind.
None of the above is legal advice — your own regulatory affairs team owns the final compliance position for your import and your finished product. What we commit to is giving you accurate product identity data, an honest statement of the hazard classification and complete documentation to work from.
From enquiry to delivered pallet
Send the specification
Product name or CAS 88-51-7, the assay and salt form you work to, quantity, pack preference and destination port.
Receive a firm quote
Pricing, lead time, packing and Incoterm confirmed in writing within 24 hours — our sourcing desk is staffed around the clock.
Qualify and approve
Sample dispatched if you are qualifying a new source. Batch COA and, where relevant, a shade comparison shared for your approval before the material is released.
Ship and track
Classification filed, freight booked, export documents issued, and the consignment tracked through transit and clearance to your plant.
Often bought alongside this grade
Consolidate several pigment and dye intermediates onto one shipment and one invoice. These are the coupling components and amino-sulfonic acids our pigment and ink customers most often order in the same programme.
What buyers ask us about 2B Acid
Is 2B Acid the same thing as CLT Acid?
Is this material hazardous?
Do you supply the free acid or the sodium salt?
What purity do you normally supply?
What is the minimum order quantity?
How long does delivery take?
Why does the powder sometimes show slight colour drift in storage?
How should we store it, and what is the shelf life?
Is this a dangerous good? What paperwork comes with it?
- Batch certificate of analysis
- GHS-format safety data sheet
- Transport classification documentation where applicable
- Commercial invoice, packing list and bill of lading or airway bill
- Certificate of origin and any destination-specific forms
Do you supply to my country?
Do you manufacture this yourself?
Can you hold stock against a production plan?
Request pricing on 2B Acid
Send your required assay, salt form, quantity, pack format and destination port. Our sourcing desk is available 24 hours a day, 7 days a week, and comes back with pricing, lead time and packing options — whether that is a single trial bag or a contracted container programme for the year.