Introduction
Dimethyl sulfate (DMS, CAS 77-78-1), also called sulfuric acid dimethyl ester, is a clear and colorless liquid that ranks among the most important industrial methylating agents. Its high reactivity and relatively low cost make it a standard reagent for introducing methyl groups into pharmaceuticals, agrochemicals, dyes, and specialty chemicals. Because it is also highly toxic and corrosive, dimethyl sulfate is always handled in closed systems under strict safety controls.
Chemical and Physical Properties
Dimethyl sulfate is the dimethyl ester of sulfuric acid. It is a polar, water-reactive liquid that methylates nucleophiles readily and hydrolyzes in the presence of water or alkali.
| Property | Value |
|---|---|
| CAS number | 77-78-1 |
| Molecular formula | C2H6O4S |
| Molecular weight | 126.13 g/mol |
| Appearance | Clear and colorless liquid |
| Boiling point | About 188 C (with decomposition) |
| Density | About 1.33 g/cm3 at 20 C |
| SMILES | COS(=O)(=O)OC |
Production
Dimethyl sulfate is produced industrially by reacting sulfur trioxide with dimethyl ether, or by the reaction of methanol with chlorosulfonic acid. In both routes the crude ester is purified by distillation to remove acidic impurities and water, which is why acidity and water content are the key specification parameters for the commercial product. Because the material is toxic and moisture sensitive, production and handling are normally carried out in closed, well-ventilated systems.
Methylation Chemistry
Dimethyl sulfate acts as a methylating agent by transferring a methyl group to a nucleophile, typically through a bimolecular (SN2-type) mechanism. The leaving group is a methyl sulfate half-ester, which is itself reactive and can methylate a second substrate or be hydrolyzed during workup. Key reaction families include:
- N-methylation and quaternization of amines, including tertiary amines to quaternary ammonium salts.
- O-methylation of phenols and alcohols to methyl ethers.
- S-methylation of thiols and thiophenols.
- C-methylation of activated carbon nucleophiles, such as enolates and aromatic rings under special conditions.
Major Industrial Applications
Pharmaceuticals
Dimethyl sulfate is used to install methyl groups in the synthesis of active pharmaceutical ingredients and intermediates, including N-methyl and O-methyl products. Its efficiency allows methylation in a single, well-controlled step.
Agrochemicals
In agrochemical manufacture, dimethyl sulfate methylates intermediates used in herbicides, fungicides, and plant growth regulators.
Dyes and Pigments
Dye chemistry relies on dimethyl sulfate for the methylation of hydroxyl and amino groups, which shifts color and improves the fastness of many dyes and pigments.
Surfactants and Quaternization
Quaternization of tertiary amines with dimethyl sulfate produces cationic surfactants, fabric softeners, and antistatic agents. A common example is the quaternization of long-chain amines to give cationic surface-active compounds.
Other Uses
Dimethyl sulfate is also used to prepare methyl esters, to methylate cellulose and starch derivatives, and as a laboratory reagent for analytical methylation.
Handling, Safety and Storage
Dimethyl sulfate is a highly toxic, corrosive liquid and a suspected carcinogen. It can cause severe skin and eye damage and serious delayed effects after inhalation or skin contact, and its vapor is dangerous even at low concentrations. The following controls are essential:
- Handle in closed systems or fume hoods with local exhaust ventilation.
- Use chemical-resistant gloves, goggles or a face shield, and protective clothing; never handle with bare hands.
- Avoid any contact with moisture, alkalis, and oxidants; store the container tightly closed in a cool, dry, well-ventilated place.
- Keep emergency showers, eyewashes, and specific antidote procedures available, and train operators in the safety data sheet.
Quality and Specifications
Typical commercial specifications for dimethyl sulfate are shown below. Assay, acidity, and appearance are the parameters most often specified by buyers.
| Parameter | Specification |
|---|---|
| Appearance | Clear and colorless liquid |
| Assay | 99.0% min |
| Acidity | 0.3% max |
Frequently Asked Questions about Dimethyl Sulfate
What is dimethyl sulfate used for?
It is used mainly as a methylating agent in pharmaceutical, agrochemical, dye, and surfactant production, and as a laboratory reagent for methylation.
How is dimethyl sulfate produced?
Industrially it is produced by the reaction of sulfur trioxide with dimethyl ether, or by reacting methanol with chlorosulfonic acid, followed by distillation purification.
Is dimethyl sulfate dangerous?
Yes. Dimethyl sulfate is highly toxic, corrosive, and a suspected carcinogen. It must be handled in closed systems with strict personal protective equipment and ventilation.
How should dimethyl sulfate be stored?
Store it cool, dry, and tightly sealed, away from moisture, alkalis, and oxidants, in a well-ventilated area under the controls described in the safety data sheet.
Where can I buy dimethyl sulfate?
PolyBlueChem supplies dimethyl sulfate (CAS 77-78-1) with COA and MSDS. Contact our team for specifications, packaging, and a quotation.
References
- PubChem Compound Summary for dimethyl sulfate (CAS 77-78-1).
- Manufacturer specification sheets for industrial-grade dimethyl sulfate.
- Occupational safety and handling guidance for dimethyl sulfate.
Disclaimer: This article is provided for general informational purposes only and does not constitute technical, regulatory, or safety advice. Dimethyl sulfate is a highly toxic material; always refer to the current safety data sheet and applicable regulations before handling it.
PolyBlueChem, as the chemical supplier of all categories, is the supplier of dimethyl sulfate (CAS 77-78-1) as well. Contact our team for specifications, packaging and a quotation.