4 B Acid
A high-purity aminotoluenesulfonic acid, supplied as 2-amino-5-methylbenzenesulfonic acid for use as an azo coupling component across pigment and dye manufacture.
What is 4 B Acid?
4 B Acid, formally 2-amino-5-methylbenzenesulfonic acid, is an off-white to pale cream crystalline powder built on a benzenesulfonic acid ring carrying an amino group at C-2 and a methyl group at C-5.
That arrangement is the reason the molecule is valuable. The amino group is diazotized and then coupled to a partner component, and the position of the methyl group on the ring controls where that coupling lands and how the resulting azo chromophore behaves — its shade, its crystal form, and its fastness once it's built into a finished pigment or dye.
At Chelora Dyes, 4 B Acid is crystallised and dried to a controlled particle profile and low moisture, so diazotization and coupling reactions downstream run cleanly and give a consistent, reproducible shade batch to batch.
- Appearance
- Off-white / pale cream
- Odour
- Faint, characteristic
- Solubility
- Water, dilute alkali
- Function
- Coupling component
- Grade
- Technical / pigment
Benzenesulfonic acid ring with amino and methyl substituents
- Molecular formulaC7H9NO3S
- Molecular weight187.21 g/mol
- IUPAC name2-Amino-5-methylbenzenesulfonic acid
- Functional groupsAmine, sulfonic acid, alkyl
- CAS number88-44-8
Technical product information
Standard specification for Chelora Dyes' technical grade 4 B Acid. Custom-grade and bulk specifications are available on request.
| Chemical name | 4 B Acid |
|---|---|
| Synonyms | 2-Amino-5-methylbenzenesulfonic acid, 2-Amino-p-toluenesulfonic acid |
| CAS number | 88-44-8 |
| Molecular formula | C7H9NO3S |
| Molecular weight | 187.21 g/mol |
| Assay (purity) | ≥ 98.0% |
| Appearance | Off-white to pale cream crystalline powder |
| Melting / decomposition point | > 280°C (decomposes) |
| Moisture content | ≤ 1.0% |
| Insoluble matter | ≤ 0.2% |
| Solubility | Soluble in water and dilute alkali; slightly soluble in alcohol |
| Packaging | 25 kg / 50 kg bags, 500–1000 kg jumbo bags |
| Shelf life | 24 months in sealed original packaging |
Applications of 4 B Acid
Azo pigment synthesis
Diazotized and coupled to build yellow, orange and red azo pigments used across printing inks and plastics.
Reactive & direct dyes
Used as a coupling component in textile dye chemistry where shade consistency and fastness are critical.
Pigment dispersions
Feeds into pigment intermediates used in masterbatch, coatings and printing ink formulation.
Fine chemical intermediates
Supplies an aminotoluenesulfonic acid core for further condensation and heterocycle chemistry.
Leather & paper dyes
Applied in smaller volumes across leather finishing and paper dye formulation.
Analytical reagents
Used as a reference and coupling reagent in analytical and research-scale dye chemistry.
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 bags to jumbo-bag bulk quantities.
Technical support
Process, coupling, and compliance guidance from our chemistry team.
Storage and guidelines
- Store in tightly sealed original packaging in a dry environment.
- Keep in a cool, dry, well-ventilated area away from direct sunlight and heat.
- Protect from moisture pickup — the powder can cake if exposed to humid air.
- Segregate from strong oxidising agents and strong acids.
- Use compatible containers: lined HDPE bags or drums.
- Re-seal bags promptly after use to preserve moisture and assay specification.
Handling precautions
4 B Acid is a fine crystalline powder that can cause irritation to skin, eyes and the respiratory tract if handled without controls.
Use dust control measures, chemically resistant gloves, and eye protection during weighing, charging, and any bulk handling operation.
Provide local exhaust ventilation where dust generation is likely, and avoid breathing dust.
Refer to the full Safety Data Sheet for exposure limits, spill containment, disposal, and first-aid measures before use.
Frequently asked questions
What is 4 B Acid used for?
4 B Acid is diazotized and used as a coupling component in the synthesis of azo dyes and pigments, contributing yellow, orange and red shades used in printing inks, textile dyeing and pigment dispersions.
How is 4 B Acid different from 2B Acid?
Both are aminotoluenesulfonic acids used as coupling components, but 4 B Acid carries only a methyl group alongside the amino and sulfonic acid functions, without the additional chlorine substituent found in 2B Acid. This gives a slightly different shade and solubility profile in the finished pigment.
Is 4 B Acid soluble in water?
Yes. As a sulfonic acid it is readily soluble in water and in dilute alkali, which is why diazotization and coupling are normally carried out directly in an aqueous medium.
What purity do you supply?
Standard technical grade is supplied at a minimum assay of 98%, with moisture and insoluble matter held within tight limits. Higher assay grades can be manufactured to order for sensitive pigment applications.
What packaging sizes are available?
25 kg and 50 kg multiwall paper or HDPE-lined bags, with bulk supply available in 500 kg and 1000 kg jumbo bags.
How should it be stored, and for how long?
In sealed original packaging in a cool, dry, ventilated store away from strong oxidisers. Shelf life is 24 months from manufacture when storage conditions are maintained.
Is it hazardous to handle?
It is an irritant and should be handled with standard PPE, dust control and adequate ventilation. Review the Safety Data Sheet before any handling operation.
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 solubility.
