Ortho Tolidine Base
A benzidine-type diamine, supplied as 3,3'-dimethylbenzidine for tetrazotization into diarylide pigment intermediates across pigment and dye manufacture.
What is Ortho Tolidine Base?
Ortho Tolidine Base, formally 3,3'-dimethylbenzidine, is a biphenyl diamine built from two linked benzene rings, each carrying an amino group and a methyl group in a symmetrical arrangement.
That symmetry is the reason the molecule anchors an entire family of pigments. Both amino groups are tetrazotized and each half of the molecule is then coupled to a separate acetoacetanilide-type component, producing a disazo, or "diarylide," chromophore. The two methyl groups set the electronic character of the ring and influence the crystal form, tinting strength and heat stability of the finished pigment.
At Chelora Dyes, Ortho Tolidine Base is crystallised and dried to a controlled particle profile, low moisture and consistent colour, so tetrazotization and double coupling reactions downstream run cleanly and give a reproducible shade batch to batch.
- Appearance
- Off-white to greyish crystalline
- Odour
- Faint, characteristic
- Solubility
- Dilute acids, alcohol, ether
- Function
- Tetrazo pigment precursor
- Grade
- Technical / pigment
Symmetrical biphenyl diamine core
- Molecular formulaC14H16N2
- Molecular weight212.30 g/mol
- IUPAC name3,3'-Dimethylbenzidine
- Functional groupsTwo aromatic amines, two alkyl
- CAS number119-93-7
Technical product information
Standard specification for Chelora Dyes' technical grade Ortho Tolidine Base. Custom-grade and bulk specifications are available on request.
| Chemical name | Ortho Tolidine Base |
|---|---|
| Synonyms | 3,3'-Dimethylbenzidine, o-Tolidine, OT Base |
| CAS number | 119-93-7 |
| Molecular formula | C14H16N2 |
| Molecular weight | 212.30 g/mol |
| Assay (purity) | ≥ 98.0% |
| Appearance | Off-white to pale grey crystalline powder |
| Melting point | 129–131°C |
| Moisture content | ≤ 0.5% |
| Insoluble matter | ≤ 0.2% |
| Solubility | Insoluble in cold water; soluble in dilute acids, alcohol and ether |
| Packaging | 25 kg lined fibre drums or bags; jumbo bags on request |
| Shelf life | 24 months in sealed original packaging |
Applications of Ortho Tolidine Base
Diarylide yellow pigments
Tetrazotized and double-coupled to build high-strength diarylide yellow pigments used in printing inks and plastics.
Diarylide orange pigments
Core precursor for diarylide orange grades used in packaging inks and masterbatch colouration.
Pigment dispersions
Feeds into pigment intermediates used across coatings, textile printing and flexographic ink formulation.
Fine chemical intermediates
Supplies a benzidine-type diamine core for further condensation chemistry.
Analytical reagents
Used in controlled laboratory-scale reference and coupling studies.
Research applications
Applied under controlled conditions in academic and industrial dye chemistry research.
Why choose Chelora Dyes
Consistent purity
Assay controlled at ≥98% with moisture and colour verified before dispatch.
Full documentation
COA, SDS, and regulatory data supplied with every shipment.
Flexible volumes
From 25 kg drums to jumbo-bag bulk quantities.
Technical support
Process, tetrazotization, and compliance guidance from our chemistry team.
Storage and guidelines
- Store in tightly sealed original packaging, protected from light.
- Keep in a cool, dry, well-ventilated area away from heat and sunlight.
- Minimise air exposure during transfer to limit surface discolouration.
- Segregate from strong oxidising agents and strong acids.
- Use dedicated, closed handling equipment and compatible containers.
- Re-seal drums promptly after use to preserve assay specification.
Handling precautions
Ortho Tolidine Base is a substance of concern that requires dedicated handling controls; it must be treated according to its Safety Data Sheet and applicable regulatory classification before any use.
Use closed, engineered handling systems, dust and vapour extraction, and full-body PPE including chemically resistant gloves, goggles and respiratory protection during weighing, charging and any bulk handling operation.
Avoid skin contact, inhalation of dust, and any release to the environment. Dedicated washing facilities should be available wherever this material is handled.
Refer to the full Safety Data Sheet for exposure limits, spill containment, disposal, and first-aid measures, and consult your local regulations governing benzidine-type substances before use.
Frequently asked questions
What is Ortho Tolidine Base used for?
Ortho Tolidine Base is tetrazotized and used as the core precursor in the manufacture of diarylide (disazo) pigments, which supply strong yellow, orange and red shades to printing inks, plastics masterbatch and coatings.
Is Ortho Tolidine Base the same as o-Tolidine?
Yes. Ortho Tolidine Base, o-Tolidine and 3,3'-dimethylbenzidine all refer to the same compound, CAS 119-93-7, a biphenyl carrying two amino groups and two methyl groups symmetrically placed on the ring system.
Is Ortho Tolidine Base soluble in water?
It is essentially insoluble in cold water. It dissolves readily in dilute mineral acids, where it is used in solution for the tetrazotization step, and it is also soluble in alcohol and ether.
What purity do you supply?
Standard technical grade is supplied at a minimum assay of 98%, with moisture and colour held within tight limits to ensure consistent tetrazotization and downstream pigment shade.
What packaging sizes are available?
25 kg fibre drums or multiwall bags with an inner liner, with bulk supply available in jumbo bags on request.
How should it be stored, and for how long?
In sealed original packaging, in a cool, dark, dry, ventilated store protected from light and air to limit discolouration. Shelf life is 24 months from manufacture when storage conditions are maintained.
Is it hazardous to handle?
Ortho Tolidine Base is classified as a substance of concern and must be handled strictly according to its Safety Data Sheet, with dedicated PPE, closed handling and engineering controls to minimise exposure.
Do you provide a Certificate of Analysis?
Yes. Each batch ships with a Certificate of Analysis and Safety Data Sheet covering assay, moisture, appearance and melting point.
