Ortho Tolidine Base
Ortho Tolidine Base (o-Tolidine) is the methylated cousin of 3,3'-Dichlorobenzidine — a benzidine-class diamine used chiefly to make Pigment Yellow 16, disclosed here with the same probable-carcinogen classification and the same plain, complete hazard statement we give every product at this tier.
What Ortho Tolidine Base is, and why buyers source it
A working overview of the compound's chemistry, its place in the aniline-derivative family, and the grades Chelora Chemicals keeps in regular supply.
We state this clearly and early, exactly as we do for every carcinogen-classified product in our range: Ortho Tolidine (3,3'-dimethylbenzidine) carries a harmonised EU CLP classification of Carcinogen Category 1B (H350), an IARC Group 2B classification ("possibly carcinogenic to humans," assigned in IARC Supplement 7, 1987), and a US National Toxicology Program listing as "reasonably anticipated to be a human carcinogen" (first listed 1983). As with its dichloro relative elsewhere in this part of our range, this is the probable/presumed/possible tier across all three systems — supported by sufficient evidence in animal studies, not confirmed human carcinogenicity — and we state it at that precise level rather than rounding in either direction.
A correction worth making plain, since getting the CAS number right matters for ordering accuracy: the correct CAS Registry Number for this substance is 119-93-7. We want to flag that an easily-mistyped near-neighbour, 119-93-5, does not correspond to this compound in any source we checked and should not appear on an order or shipping document for this product. Chemically, o-Tolidine's real documented industrial use is acetoacetylation followed by coupling with diazotised 2,4-dichloroaniline to give Pigment Yellow 16 — a distinct pigment from the Pigment Yellow 12/13/14/17 family made from 3,3'-dichlorobenzidine. We want to correct a plausible-sounding but inaccurate assumption directly: o-Tolidine is not a documented route to Pigment Yellow 12 or 13 — those are made from the dichloro diamine, not this one.
Where it fits in the synthesis chain
We supply the free-base diamine itself. We do not manufacture or supply Pigment Yellow 16 or any other finished pigment made from it.
Grades we supply
95% and 98% grades are both seen across the trade.
How Ortho Tolidine Base is made
An overview of the production route for orientation purposes. Our manufacturing partners' own process parameters and in-process controls are proprietary and are not disclosed beyond what is needed to interpret the certificate of analysis.
Ortho Tolidine is made industrially from 2-nitrotoluene: reduction (analogous to the route used for its dichloro relative) gives 2,2'-dihydrazotoluene, which undergoes the same acid-catalysed benzidine rearrangement to give the 4,4'-diaminobiphenyl structure, methylated at both 3,3'-positions rather than chlorinated.
The free base is purified by crystallisation and tested for isomeric purity, residual starting material, and free-amine content before release — the finished pigment manufacturer's downstream acetoacetylation and coupling chemistry requires well-characterised input to achieve consistent shade.
The same benzidine-rearrangement chemistry connects this compound structurally to 3,3'-dichlorobenzidine elsewhere in our range, differing only in the substituent (methyl here, chlorine there) installed before the rearrangement step — which is why the two compounds share so much of their hazard profile despite feeding different pigments downstream.
A correction worth stating plainly: not the same downstream pigments as its dichloro relative
It would be a reasonable assumption that this compound and 3,3'-dichlorobenzidine feed the same or overlapping diarylide pigments, since they're structurally so similar. The documented chemistry doesn't support that: o-Tolidine's real, sourced downstream product is Pigment Yellow 16, made by a different coupling sequence (acetoacetylation then coupling with diazotised 2,4-dichloroaniline) than the double-diazotisation route used for the dichloro diamine's Pigment Yellow 12/13/14/17 family. We correct this directly rather than let a plausible-sounding assumption stand uncorrected.
Industries and processes that use it
Ortho Tolidine Base is consumed almost entirely as a synthesis intermediate. The four fields below account for most of the demand we see through our export desk.
Pigment Yellow 16 Manufacture
Acetoacetylation with diketene, followed by coupling with diazotised 2,4-dichloroaniline, gives Pigment Yellow 16 — the documented, sourced downstream product of this specific diamine.
Soluble Azo Dyes & Toner Chemistry
Used more broadly in soluble azo dye and toner chemistry beyond the single named pigment above.
Historical Chlorine Test-Kit Reagent (Declining Use)
Historically the dominant reagent in free-available-chlorine test kits for pools and municipal water, now substantially displaced by DPD-based methods due to both accuracy limitations and this compound's hazard profile — we note this historical use for completeness, not as a current recommended application for material supplied by us.
How the molecule is typically carried forward
Ortho Tolidine's reaction chemistry is defined by its two amino groups, which is exactly what connects it structurally to 3,3'-dichlorobenzidine even though the two feed different pigment products.
Acetoacetylation
Reaction with diketene installs an acetoacetyl group on the amine, the first step in the documented route to Pigment Yellow 16 — a different first step from the double diazotisation its dichloro relative undergoes.
Coupling with diazotised 2,4-dichloroaniline
The acetoacetylated intermediate couples with separately diazotised 2,4-dichloroaniline to build the azo structure that defines Pigment Yellow 16.
Diazotisation (test-kit and specialty chemistry)
The free amine itself can also be diazotised under standard conditions, relevant to its historical chlorine-test-kit use and to specialty azo dye chemistry beyond the named pigment above.
Ortho Tolidine Base against its near relatives
Ortho Tolidine Base and 3,3'-Dichlorobenzidine Dihydrochloride are the two benzidine-class diamines in our range — close structural relatives, both classified as probable carcinogens, but feeding two distinct and non-overlapping sets of diarylide pigments.
| Product | CAS Number | Typically Used In | Notes |
|---|---|---|---|
| Ortho Tolidine Base | 119-93-7 | Pigment Yellow 16 and related soluble azo dyes/toners | The product on this page. EU Carc. 1B, IARC Group 2B. |
| 3,3'-Dichlorobenzidine Dihydrochloride | 612-83-9 | Pigment Yellow 12/13/14/17/55/63/83; Pigment Orange 13/34 | Also supplied — see its product page. EU Carc. 1B, IARC Group 2B. |
Exact physical constants and purity specifications are confirmed per batch on the certificate of analysis — treat the notes above as a sourcing guide rather than a specification sheet.
Safety classification at a glance
Based on GHS classification as commonly listed for this substance. This is a summary for orientation only — always work from the current safety data sheet supplied with your specific batch.
May cause cancer.
Harmful if swallowed.
Toxic to aquatic life with long lasting effects.
Danger
Ortho Tolidine carries a harmonised EU CLP Annex VI classification (Index 612-041-00-7): Carc. 1B (H350), Acute Tox. 4 oral (H302), and Aquatic Chronic 2 (H411). A separate generic Annex VI entry (Index 612-081-00-5) covers salts of 3,3'-dimethylbenzidine in parallel. IARC classifies this substance Group 2B ("possibly carcinogenic to humans"), assigned in Supplement 7 (1987) following an earlier 1972 review that assessed the animal data without yet assigning a group. The US National Toxicology Program lists it as "reasonably anticipated to be a human carcinogen" (first listed 1983) and separately lists "3,3'-dimethylbenzidine-based dyes" (metabolised to this amine in the body) under the same status (first listed 2002) — a distinct listing covering finished dyes, not this intermediate itself. We state plainly: this is the probable/presumed/possible tier across all three systems, not the confirmed/known tier.
Keeping it on spec between delivery and use
General storage guidance for this grade. Site-specific storage rules, segregation requirements and re-test intervals should follow your own EHS procedures and the MSDS issued with your batch.
Store in a cool, dry, well-ventilated, access-controlled area consistent with Carc. 1B handling requirements. Full PPE is required for all handling, including respiratory protection where dust generation is possible. Keep containers tightly sealed and clearly labelled.
How it ships from Indonesia
Standard packing and export terms for this product. Confirm exact figures against your order — they vary slightly by destination and quantity.
What travels with every batch
Specification is agreed before the purchase order, not discovered on arrival. Every shipment of Ortho Tolidine Base leaves with a documented, checkable paper trail.
Certificate of Analysis
Batch-wise assay (by GC), isomer purity, melting point range and moisture, issued against the agreed specification so your QC team can check it, not just file it.
Safety Data Sheet
GHS-format SDS in English covering hazard classification, handling, storage, first-aid and spill response for the exact grade shipped.
Technical Data Sheet
Reference physical and chemical properties, recommended storage and typical applications, for internal circulation to your process or R&D teams.
Certificate of Origin
Confirms Indonesian origin for customs clearance and any preferential-duty claim at your destination port.
Dangerous Goods Declaration
UN packing group, classification and shipper's declaration prepared ahead of loading so documentation never holds up customs.
Third-Party Inspection
Independent pre-shipment inspection and re-sampling can be arranged on request, at your cost, for buyers who require it as a matter of policy.
Frequently asked questions
What buyers most often ask our sales desk about this grade.
01What is Ortho Tolidine Base used for?+
02What is the CAS number of Ortho Tolidine Base?+
03What purity grades does Chelora Chemicals supply?+
04Is Ortho Tolidine Base hazardous?+
05Is this a confirmed human carcinogen?+
06Is the CAS number 119-93-5 or 119-93-7?+
07Does this feed the same pigments as 3,3'-Dichlorobenzidine?+
08Is this still used in chlorine/pool-water test kits?+
09What packing options are available?+
10How long does delivery take?+
11Can I get a sample before placing a bulk order?+
12How is Ortho Tolidine Base manufactured?+
13What is the shelf life, and how should it be stored?+
Need Ortho Tolidine Base on spec, on time?
Send us your required purity, quantity, packing preference and destination port. Our desk quotes most enquiries within one working day.