Dimethyl Sulfate
A high-purity methylating agent, supplied as dimethyl sulfate for N- and O-methylation of dye intermediates, quaternary ammonium compounds and fine chemicals.
What is Dimethyl Sulfate?
Dimethyl Sulfate is a colourless, faintly odorous oily liquid: the di-ester of methanol and sulfuric acid. It is the standard methylating agent of the dye industry and has been for over a century.
Its job is to hand a methyl group to a nucleophile. Amines become N-methyl amines, phenols become methyl ethers, tertiary amines become quaternary ammonium salts, and each of those transformations sits somewhere in the route to a basic dye, a disperse dye or a methylated intermediate. It is preferred over gaseous alternatives because it is a liquid that can be metered and contained, and because it works under mild conditions with good selectivity.
Those advantages come with a serious cost. Dimethyl sulfate is acutely toxic, corrosive and carcinogenic, and its effects are notoriously delayed. It should be regarded as a closed-system-only material, and the handling section below deserves reading in full before any purchase decision.
- Appearance
- Colourless oily liquid
- Odour
- Faint; poor warning
- Solubility
- Slight; hydrolyses
- Function
- Methylating agent
- Grade
- Technical
The dimethyl ester of sulfuric acid
- Molecular formulaC2H6O4S
- Molecular weight126.13 g/mol
- IUPAC nameDimethyl sulfate
- Functional groupsSulfate diester
- CAS number77-78-1
Technical product information
Standard specification for Chelora Dyes' technical grade Dimethyl Sulfate. Higher assay grades are available on request.
| Chemical name | Dimethyl Sulfate |
|---|---|
| Synonyms | Dimethyl sulphate, DMS, Methyl sulfate |
| CAS number | 77-78-1 |
| Molecular formula | C2H6O4S |
| Molecular weight | 126.13 g/mol |
| Assay (purity) | ≥ 99.5% |
| Appearance | Colourless to pale yellow oily liquid |
| Melting point | Approx. −32°C |
| Boiling point | Approx. 188°C (decomposes) |
| Density | Approx. 1.33 g/cm³ at 20°C |
| Acidity (as H2SO4) | ≤ 0.1% |
| Methanol content | ≤ 0.1% |
| Colour (APHA) | ≤ 30 |
| Solubility | Slightly soluble in water; hydrolyses slowly to methanol and sulfuric acid |
| Transport classification | UN 1595, dimethyl sulphate (verify against current documentation) |
| Packaging | 250 kg lined MS drums; ISO tanks for bulk supply |
| Shelf life | 12 months in sealed, dry, cool storage |
Applications of Dimethyl Sulfate
N-methylation of amines
Converts aniline intermediates to their N-methyl and N,N-dimethyl derivatives for dye synthesis.
Quaternary ammonium salts
Quaternises tertiary amines to build the cationic centres of basic and cationic dyes.
Methyl ethers of phenols
Methylates phenolic intermediates where an ether rather than a free hydroxyl is required.
Pharmaceutical intermediates
Applied in methylation steps across active ingredient and intermediate manufacture.
Agrochemical intermediates
Used where a methyl group must be installed in crop protection synthesis.
Surfactants and softeners
Feeds quaternised surfactant and fabric softener chemistry.
Why choose Chelora Dyes
Controlled assay
Acidity, methanol and colour held low so methylation runs clean and predictable.
Full documentation
COA, SDS, and transport classification supplied with every shipment.
Compliant logistics
Toxic goods packing and paperwork handled to the applicable transport mode.
Technical support
Closed handling, decontamination, and compliance guidance from our team.
Storage and guidelines
- Store in sealed original containers in a cool, dry, ventilated and locked store.
- Keep the store bunded, signed, and restricted to authorised trained personnel.
- Hold dilute alkali or ammonia decontamination media ready at the point of use.
- Segregate from water, alkalis, strong oxidisers and ammonia stocks in storage.
- Transfer by closed system only — no open pouring, decanting or manual sampling.
- Keep vapour detection and emergency response arrangements in place and tested.
Handling precautions
Dimethyl Sulfate is one of the most acutely dangerous materials we supply. It is fatal if inhaled, causes severe burns to skin and eyes, and is classified as a carcinogen and a suspected mutagen.
Its most treacherous property is delayed onset. The vapour gives almost no warning at harmful concentrations, and serious injury to the eyes and respiratory tract can develop several hours after an exposure that felt trivial. Anyone with suspected exposure must be removed from the area and placed under medical observation regardless of how they feel.
Handle in fully closed systems under a written procedure, by trained operators only, with full chemical protective clothing, gloves and respiratory protection appropriate to the task. Dilute alkali or ammonia hydrolyses the material and should be available as decontamination media wherever it is stored or used.
Arrange medical support and emergency response in advance rather than at the point of incident, and refer to the current Safety Data Sheet in full before any handling operation.
Frequently asked questions
What is Dimethyl Sulfate used for?
It is the workhorse methylating agent of the dye industry. It transfers a methyl group to amines, phenols and other nucleophiles, which is how N-methylated aniline intermediates, methylated phenols and quaternary ammonium compounds for basic dyes are made. It is also used across pharmaceutical and agrochemical synthesis.
Why is it preferred over methyl chloride or methanol?
It is a liquid at ambient conditions, so it is easier to meter and contain than a gas, and it methylates under milder conditions and at better selectivity than most alternatives. Those handling advantages are the reason it remains in use despite its severe toxicity.
Why is delayed onset of symptoms so important?
Because exposure does not announce itself. The vapour gives little immediate warning, and serious injury to the eyes and respiratory tract can develop over several hours after an exposure that seemed minor at the time. Anyone with suspected exposure must be removed from the area and placed under medical observation, whether or not they feel unwell.
How is it decontaminated?
Dilute alkali or ammonia solution hydrolyses it to harmless products, and decontamination media should be kept ready wherever the material is handled or stored. The specific method and concentrations are given in the Safety Data Sheet and should be built into your written procedures.
Is it soluble in water?
Only slightly, and it hydrolyses slowly in contact with water to methanol and sulfuric acid. Hydrolysis is faster in warm or alkaline conditions, which is the basis of the decontamination method.
What purity do you supply?
Standard grade is supplied at a minimum assay of 99.5%, with acidity, methanol content and colour held within tight limits. Higher assay grades can be supplied to order.
What packaging is available?
250 kg lined mild steel drums, and ISO tanks for bulk supply to plants with closed offloading systems. We review receiving arrangements before first shipment.
Is it hazardous to handle?
Yes. This is one of the most acutely dangerous materials in the range. It is fatal if inhaled, causes severe burns to skin and eyes, is classified as a carcinogen and a suspected mutagen, and its effects can be delayed by several hours. It must only be handled in fully closed systems by trained operators under a written procedure, with decontamination media and medical support arranged in advance.
