Ortho-Tolidine Base
Ortho-tolidine is a two-ended coupling intermediate — a biphenyl diamine that can be tetrazotised at both ends and coupled twice, which is exactly what gives the resulting dyes their substantivity and their depth of shade. Everything commercially interesting about this molecule follows from those two amino groups sitting on opposite ends of the same rigid backbone.
Chelora Chemicals supplies ortho-tolidine base to dye and pigment producers worldwide, in UN-approved packing, with a batch COA and GHS safety data sheet on every consignment.
Product identity
- CAS Number
- 119-93-7
- IUPAC name
- 3,3′-Dimethyl-[1,1′-biphenyl]-4,4′-diamine
- Molecular formula
- C₁₄H₁₆N₂
- Molecular weight
- 212.29 g/mol
- EC / EINECS
- 204-358-0
- UN Number
- 2811 · Class 6.1*
- SMILES
- Cc1cc(ccc1N)-c1ccc(N)c(C)c1
- HS Code
- 2921 59*
* Confirm the exact UN entry, packing group and HS heading with your freight forwarder and customs broker — aromatic diamines are classified against the destination's own schedule and the shipping description can differ by mode and by country.
What Ortho-Tolidine Base is used for
Ortho-tolidine base is a white to light grey or faintly pink crystalline solid, a biphenyl carrying an amino group on each ring and a methyl group ortho to each amine. Those two methyls are not decoration — they twist the rings out of plane and shift the absorption of the finished dye, which is why o-tolidine and plain benzidine give visibly different shades from the same coupling component.
Its dominant use is as a bis-diazo coupling intermediate. The base is tetrazotised in cold mineral acid with sodium nitrite, then coupled — usually twice — onto naphthol sulfonic acids, acetoacetanilides or pyrazolones to build direct dyes for cotton, paper and leather, and to build organic pigments where a high-molecular-weight, low-solubility colourant is wanted.
Where it sits among coupling intermediates
- Ortho-tolidine (this product) two methyl groups ortho to the amines; gives the classic tolidine-based direct blues and reds.
- Ortho-dianisidine the methoxy analogue, CAS 119-90-4, shifting shade further toward blue at higher cost.
- 3,3′-Dichlorobenzidine the chloro analogue, the backbone of the diarylide yellow and orange pigment family.
- Mono-functional amines such as N,N-dimethylaniline couple once only, giving simpler, more soluble dyes.
On a restricted aromatic amine, confirm the CAS number and the permitted end use on your purchase order — see the full dye intermediate range.
Appearance and handling character
The material ships as a crystalline powder or flake that darkens on exposure to air and light, practically insoluble in water but readily soluble in dilute mineral acid as the diammonium salt — which is how it enters the tetrazotisation vessel. It is classified as a carcinogen and a skin sensitiser, and it is very toxic to aquatic life. Dust control is the single most important engineering question on this product; the safety section below should be read before any handling is planned.
| Parameter | Typical value |
|---|---|
| Appearance | White to light grey / pink crystalline powder or flake |
| Assay (HPLC) | 99.0% min |
| Melting range | 127 – 131 °C |
| Moisture | 0.5% max |
| Sulphated ash | 0.1% max |
| Insolubles in dilute HCl | Reported per batch |
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. Assay and melting range are the figures that most affect coupling yield and final shade — tell us your target and we will quote against it.
| Property | Value |
|---|---|
| Physical state | Crystalline solid at ambient |
| Melting point | 129 – 131 °C |
| Boiling point | ≈ 300 °C |
| Bulk density | ≈ 1.17 g/cm³ |
| Water solubility | Practically insoluble; soluble in dilute mineral acid |
| Solvent solubility | Soluble in alcohol, ether, glacial acetic acid |
Physical constants compiled from public reference data for CAS 119-93-7 and rounded for readability. Treat them as orientation, not as a specification.
Where our customers put this intermediate to work
This is a colour-chemistry workhorse. The interest is always in the shade and the fastness that come out at the far end of the coupling.
Direct dye manufacture
Tetrazotised and double-coupled onto naphthol sulfonic acids to produce substantive direct dyes for cotton, viscose, paper and leather.
- Direct blue and direct red ranges
- Shade-critical specification on request
- See our dye intermediate range
Organic pigment synthesis
Coupled onto acetoacetanilide and pyrazolone components to give high-molecular-weight pigments for inks, coatings and plastics masterbatch.
- Disazo pigment routes
- Particle-size and strength critical
- Technical desk review of your route
Diazonium salt preparation
Converted to stabilised tetrazonium salts for sale as a dry colour base, letting downstream dyers couple on site without running a nitrosation.
- Fast colour base manufacture
- Low free-amine specification available
- Custom quantities on request
Leather & paper colourants
Tolidine-based direct dyes remain widely specified where substantivity to cellulose and a deep, even shade matter more than top-end light fastness.
- Paper and board dyeing
- Leather finishing colourants
- Full impurity profile on request
Analytical & laboratory reagent
Small-scale use in colourimetric test methods and as a reference standard in dye analysis, handled under the same strict controls as plant scale.
- Small DG-compliant packs
- Full analytical documentation available
- Reference-grade material on request
Contract & scheduled supply
Dye houses consume this intermediate on campaign cycles. We hold inventory and release it against your production calendar.
- Annual contracts with scheduled call-off
- Price held across the contract period
- Second source held in reserve
How we supply Ortho-Tolidine Base
Chelora Chemicals is a supplier and sourcing partner, not a manufacturer. On a restricted aromatic amine, owning no plant means we are never selling you whatever a captive unit happens to be running — we route your order to the producer whose packaging, dust control and documentation actually match a controlled handling protocol.
We place your order with whichever qualified producer best matches your assay, your shade 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 an environmental inspection, your order switches source rather than stalling.
- Assay and melting range confirmed before we quote. 99% min with a tight melting range is the commercial standard — we state both figures on the COA.
- Carcinogen classification stated up front. We say so at enquiry stage, every time, so your EHS team can plan dust control before the first drum arrives.
- End-use and destination restrictions checked first. Aromatic amine rules differ sharply by country and by end use — we check before you raise the PO, not after.
- Batch COA shared before dispatch. You approve assay and melting range against your own spec while the material is still in our warehouse.
- Pre-shipment samples for shade qualification. New account or new source, your laboratory runs a trial coupling before the full quantity ever moves.
- Export machinery handled in-house. Classification, approved packing, labelling, freight booking and customs paperwork are ours to manage.
Packed the way your plant receives it
On a dusty, carcinogen-classified powder the pack format is a safety decision before it is a cost decision. Tell us how the material will be charged at your end and we will quote the format that suits your operation.
Fibre / HDPE drums
UN-approved drums with an inner LDPE liner — the standard commercial format and the easiest to handle into a closed charging port.
Lined steel drums
Heavier-duty drums for long sea legs and humid destinations, where liner integrity over months in transit is the governing concern.
Jumbo bags (FIBC)
Lined, discharge-spout FIBCs for high-volume consumers with bulk-bag handling and dust-extracted charging stations already installed.
Trial / sample quantities
Small, DG-compliant containers dispatched so your colour laboratory can qualify the grade before committing to larger volumes.
Incoterms to suit you
Quoted on the Incoterm your purchasing team works to, with DG documentation filed before the booking is made.
Campaign despatch
We hold contracted tonnage and release it against your production calendar instead of landing it all at once.
Dust control is the controlling measure
Ortho-tolidine is an aromatic diamine carrying a carcinogen classification, a skin-sensitisation statement and acute oral toxicity, and it is very toxic to aquatic life. The summary below is orientation only — the safety data sheet supplied with your consignment is the authoritative document.
Classified hazards
H350May cause cancer.H301Toxic if swallowed.H317May cause an allergic skin reaction.H319Causes serious eye irritation.H335May cause respiratory irritation.H410Very toxic to aquatic life with long lasting effects.
Hazard statements reflect classifications commonly published for CAS 119-93-7. Benzidine-type amines are absorbed through skin as well as inhaled, and sensitised workers can react to very small later exposures. Always read the SDS issued with your specific batch.
Spill & emergency orientation
Plan your response before the pallet arrives. Sections 4, 5 and 6 of the SDS are the authoritative instructions and should be posted at the point of use.
- Never dry-sweep a spill. Sweeping re-suspends the dust and turns a contained spill into an inhalation exposure — collect with a HEPA vacuum or damp methods.
- Contain, do not hose to drain. H410 applies — collect the material and dispose of it as regulated chemical waste.
- Treat contaminated clothing as waste. Remove it immediately, bag it and handle it as contaminated waste rather than sending it to an ordinary laundry.
- Wash skin thoroughly and get it assessed. Skin contact with a sensitiser and suspected carcinogen is reportable at most sites — log the exposure, do not wave it off.
- Decontaminate surfaces and equipment. Residual powder on tools, drum rims and floors remains a contact hazard until properly cleaned down.
Storage
- Cool, dry, dark, access-controlled store. Light and air both drive the surface oxidation that discolours the powder and can shift your shade.
- Keep containers tightly closed. On a sealed and bunded floor — once the liner is opened, re-seal it properly between charges.
- Segregate from oxidising agents and acids. Aromatic amines react readily with oxidisers; keep the two apart by distance, not just by label.
- Restrict access and log entry. With a carcinogen classification, controlling who enters the store is a core control measure, not an optional one.
- Shelf life typically 24 months. In sealed original packing, away from heat and light. Re-assay before use after extended storage.
Handling & PPE
- Design dust and skin contact out. Closed transfer, contained charging and local exhaust ventilation first; PPE last, never as the sole control.
- Chemical-resistant gloves, coveralls and eye protection. With contaminated clothing removed, bagged and handled as contaminated waste.
- Respiratory protection for dust. Particulate respirators or supplied air during any operation that can generate airborne powder, per your exposure assessment.
- Health surveillance for exposed workers. Given the carcinogen classification, your occupational health provider should define a monitoring programme for routine handlers.
- Never discharge to drain or watercourse. H410 applies — contain and dispose of as regulated chemical waste.
Transport
Ortho-tolidine base generally moves as regulated cargo, most commonly under UN 2811, Class 6.1. We classify each consignment, apply UN-approved packaging and labelling, and file the dangerous-goods declaration before the booking is made — ask us for the current DG 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, melting range, moisture and ash — checked against your purchase specification before release.
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.
Dangerous Goods Declaration
UN number, hazard class and IMDG or RID/ADR declaration prepared and filed before the container is booked, with correctly marked and labelled packaging.
Certificate of Origin
Chamber-attested where required, plus preferential-origin forms where a trade agreement gives your import duty relief.
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.
Two amines, one rigid biphenyl
Both amino groups are available for diazotisation, which is the entire basis of this molecule's industrial value — one intermediate, two chromophores, one large and substantive dye. The routes below are the general industrial pattern, not a process disclosure.
Reduce ortho-nitrotoluene
Controlled reduction couples two nitrotoluene units into the corresponding hydrazo compound rather than taking them all the way to the amine.
Benzidine rearrangement
Acid treatment rearranges the hydrazo intermediate to the 4,4′-diamino biphenyl skeleton that defines the product.
Isolate and recrystallise
The base is liberated, filtered and recrystallised to lift assay and tighten the melting range before packing.
Tetrazotise and couple
In use, both amines are diazotised in cold acid with nitrite, then coupled onto the chosen component to form the finished dye or pigment.
Why assay and melting range carry through the whole route
On a coupling intermediate, small changes in purity show up directly as shade and strength variation in the finished colour:
- A broad melting range signals isomeric or positional impurity. Those impurities couple too, producing off-shade by-products that are very hard to correct downstream.
- Low assay means under-coupling. Charge on label weight rather than on assay and you leave coupling component unreacted in the vessel.
- Surface oxidation shifts shade. Darkened material can still assay well but introduce a dullness that only shows up on the dyed substrate.
- Stoichiometry is unforgiving on a bis-diazo intermediate. Each amine must be diazotised cleanly; a partial tetrazotisation gives mono-coupled species with quite different fastness.
That is why we quote against your written assay and melting-range limits rather than a generic "technical grade", and why the batch COA is shared for approval before dispatch rather than sent with the invoice.
| Material | Downstream / use |
|---|---|
| Ortho-tolidine base CAS 119-93-7 — this product | Direct dyes & disazo pigments |
| Ortho-dianisidine CAS 119-90-4 | Blue-shifted direct dyes |
| 3,3′-Dichlorobenzidine CAS 91-94-1 | Diarylide yellow & orange pigments |
| Ortho-nitrotoluene CAS 88-72-2 | Upstream feedstock to this product |
We supply across this intermediate family — see the full intermediate range. Send the CAS number and we will confirm the correct material before quoting.
What actually moves the price of this product
Knowing what drives the quote helps you time a purchase and read whether an offer is realistic.
Nitrotoluene feedstock
The route starts from ortho-nitrotoluene, so toluene nitration economics and the nitro-aromatics cycle feed straight through to price.
- Toluene tracks the aromatics market
- Nitration capacity is tightly regulated
- We flag feedstock-driven moves in the quote
Carcinogen compliance cost
Containment, dust extraction, exposure monitoring and health surveillance all sit inside the delivered price wherever they apply.
- Obligations vary sharply by jurisdiction
- We check destination rules before quoting
- Ask about documentation for your site
Freight and DG surcharges
Class 6.1 cargo carries a hazardous surcharge, and some carriers restrict routing for carcinogen-classified solids.
- Compare on landed cost, not ex-works
- DG space books out ahead of peak season
- We quote FOB, CIF, CFR or DDP as you prefer
Textile and pigment demand cycles
Demand follows the dye and printing-ink seasons; a strong textile quarter tightens availability well before it moves the headline price.
- Ask us what the dye market is doing
- Contracted call-off smooths the exposure
- We hold a second qualified source
Source availability
A plant turnaround, environmental inspection or effluent-consent review can take capacity offline at short notice on this chemistry.
- We hold a second qualified source on this line
- Qualify the alternate before you need it
- Ask us about dual-source contracts
Regulatory substitution pressure
Restrictions on azo colourants that can release regulated aromatic amines shape long-term investment in this chemistry.
- We track substitution trends on your behalf
- Ask whether an alternative suits your shade
- Long-term contracts lock in supply either way
| If your end use is… | Specify |
|---|---|
| Direct dye manufacture | 99% min assay, tight melting range, shade-critical |
| Organic pigment synthesis | Low insolubles, full impurity profile |
| Fast colour base / stabilised salt | Low free amine, low moisture |
| Laboratory / reference use | Small DG-compliant pack, full COA |
Not sure which column you are in? Describe what you make from it 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 drum
What our technical desk will do
- Confirm assay and melting range before anything else. On this intermediate both figures decide coupling yield and final shade, and we settle them in the first reply.
- Be straight about the carcinogen classification. Stated at enquiry stage so your EHS team can plan containment and dust extraction before the first delivery.
- Check the end-use restriction position. Several regions restrict azo colourants that can release regulated aromatic amines — we raise this before you commit.
- Review your specification before it goes into a contract. So you are not locked into a purity no plant can consistently hit.
Regulatory & compliance notes
- Carcinogen handling obligations are jurisdiction-specific. Several regimes impose exposure monitoring, health surveillance and record retention for this class. Confirm what applies at your site before the first delivery.
- Import controls vary by destination. We check destination rules before quoting, not after you have raised the PO.
- Chemical inventory listings differ between regions. We will supply the identity data you need for that filing.
- Effluent and waste rules matter. H410 applies — check your discharge consent against the material before introducing it to site.
None of the above is legal advice — your own regulatory affairs team owns the final compliance position for your import and your workplace. What we commit to is 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 119-93-7, your assay and melting-range requirement, 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 shared for your approval before the material is released.
Ship and track
Classification filed, DG freight booked, export documents issued, and the consignment tracked through transit and clearance to your plant.
What buyers ask us about Ortho-Tolidine Base
What is ortho-tolidine base used for?
Is ortho-tolidine a carcinogen?
Are there restrictions on buying or using it?
What purity do you normally supply?
Why does the powder darken in the drum?
What is the minimum order quantity?
How should we store it?
Is this a dangerous good? What paperwork comes with it?
Do you manufacture this yourself?
Request pricing on Ortho-Tolidine Base
Send your required assay, melting range, 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 pack or a contracted programme for the year.