Oleum 65%
Fuming sulfuric acid supplied as Oleum 65% (65% free SO3) for high-strength sulfonation duty across dye, pigment and intermediate manufacture.
What is Oleum 65%?
Oleum 65%, also called fuming sulfuric acid, is a solution of sulfur trioxide (SO3) dissolved in concentrated sulfuric acid, held at a nominal 65% free SO3 content.
The much higher free-SO3 loading compared with standard oleum makes this grade suited to sulfonation duties that demand a higher effective SO3 dose per unit volume, or that are diluted on-site to an intermediate strength. It is used to introduce sulfonic acid (–SO3H) groups onto aromatic rings across dye and intermediate manufacture.
At Chelora Dyes, Oleum 65% is manufactured and analysed to a controlled free-SO3 specification so sulfonation reactions downstream give a consistent, reproducible degree of substitution batch to batch.
- Appearance
- Colourless to dark, dense fuming oily liquid
- Odour
- Pungent, acrid
- Solubility
- Miscible with sulfuric acid; reacts violently with water
- Function
- Sulfonation reagent (high strength)
- Grade
- Technical / process chemical
Sulfur trioxide dissolved in sulfuric acid (high strength)
- CompositionH2SO4 with dissolved SO3
- Free SO3 content64–66% by weight
- Common nameFuming sulfuric acid, Oleum 65%
- Reactive speciesSO3 (electrophilic sulfonating agent)
- CAS number8014-95-7
Technical product information
Standard specification for Chelora Dyes' Oleum 65% (fuming sulfuric acid, high strength). Custom free-SO3 strengths and bulk specifications are available on request.
| Chemical name | Oleum 65% (Fuming sulfuric acid) |
|---|---|
| Synonyms | OL65, Sulfuric acid fuming 65% free SO3 |
| CAS number | 8014-95-7 |
| Composition | H2SO4 / SO3 mixture |
| Free SO3 content | 64–66% by weight |
| Appearance | Colourless to dark, dense fuming oily liquid |
| Density (20°C) | Approx. 1.97–1.99 g/cm³ |
| Iron content | Held to low ppm limits for colour-sensitive applications |
| Reactivity | Reacts violently and exothermically with water |
| Packaging | Acid-resistant drums and IBC; bulk tanker on request |
| Shelf life | 12 months in sealed original packaging |
Applications of Oleum 65%
High-strength sulfonation
Delivers a higher effective SO3 dose per unit volume for demanding aromatic sulfonation duties.
On-site dilution
Diluted with sulfuric acid or lower-strength oleum on site to reach an intermediate working strength.
Sulfonic acid dye intermediates
Used in the manufacture of heavily sulfonated azo and reactive dye intermediates.
Detergent & surfactant intermediates
Applied in high-strength sulfonation steps for anionic surfactant manufacture.
Nitration & mixed-acid processes
Used in combination with nitric acid in mixed-acid nitration systems requiring high SO3 activity.
General acid-process reagent
Applied across acid-catalysed condensation, dehydration and sulfonation reactions.
Why choose Chelora Dyes
Consistent strength
Free SO3 content controlled and verified before dispatch.
Full documentation
COA, SDS, and regulatory data supplied with every shipment.
Flexible volumes
From acid-resistant drums to bulk IBC and tanker quantities.
Technical support
Process, sulfonation, and compliance guidance from our chemistry team.
Storage and guidelines
- Store in tightly sealed, acid-resistant original containers.
- Keep in a cool, dry, well-ventilated area, away from direct sunlight.
- Store away from water and moisture at all times.
- Segregate from organic materials, bases, and reducing agents.
- Use compatible containers: steel, glass-lined or PTFE-lined vessels rated for high-strength oleum.
- Re-seal containers promptly after use to prevent moisture ingress and fuming loss.
Handling precautions
Oleum 65% is strongly corrosive to skin, eyes and the respiratory tract, and reacts violently and exothermically with water, releasing dense fumes; its higher SO3 content makes it more reactive than lower-strength oleum grades.
Use acid-resistant gloves, full face and eye protection, and a chemical apron during transfer and charging operations.
Always add oleum to the reaction medium slowly with cooling and agitation; never add water to the acid.
Refer to the full Safety Data Sheet for exposure limits, spill containment, disposal, and first-aid measures before use.
Frequently asked questions
What is Oleum 65% used for?
Oleum 65% is used as a high-strength sulfonation reagent to introduce sulfonic acid groups onto aromatic rings during dye, pigment and surfactant intermediate manufacture.
How does Oleum 65% differ from Oleum 23%?
Oleum 65% carries a much higher free-SO3 content, giving a greater effective SO3 dose per unit volume; it is often diluted on site to reach the working strength a given sulfonation step requires.
Is Oleum 65% soluble in water?
It reacts violently and exothermically with water rather than simply dissolving, so it must always be added slowly to water or the reaction medium, never the reverse.
What free SO3 strength do you supply?
Standard grade is supplied at 64–66% free SO3 by weight; the 23% grade is also available for lower-strength duties.
What packaging is available?
Acid-resistant drums and IBC totes as standard, with bulk tanker supply available on request.
How should it be stored, and for how long?
In sealed, acid-resistant original containers in a cool, dry, ventilated store, strictly isolated from water and moisture. Shelf life is 12 months from manufacture when storage conditions are maintained.
Is it hazardous to handle?
Yes, it is strongly corrosive and reacts violently with water, so it must be handled with full acid-resistant PPE 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 free SO3 content, density, and appearance.