Dimethyl sulfoxide (DMSO, CAS 67-68-5) is a sulfur-containing organic solvent. At room temperature it is a transparent, slightly hygroscopic liquid with a faint bitter taste, and it is classed as a combustible liquid. Its combination of high polarity, a high boiling point, good thermal stability, aprotic behaviour and complete water miscibility has earned it the informal name of universal solvent.
Physical and Chemical Properties
| Property | Typical value |
|---|---|
| Chemical name | Dimethyl sulfoxide |
| CAS number | 67-68-5 |
| Molecular formula | C2H6OS |
| Molecular weight | 78.13 |
| Boiling point | 189 °C |
| Melting point | 18.5 °C |
| Density at 20 °C | About 1.10 g/cm3 |
| Dielectric constant | About 46.7 |
| Refractive index (20 °C) | About 1.479 |
| Solubility | Miscible with water, alcohols, ketones and aromatics |
| Odour | Low, faint sulfurous note |
Chemical Stability and Solvency
DMSO does not decompose readily at normal processing temperatures, so it holds its performance in complex synthesis environments. Its high dielectric constant raises reaction rates and improves extraction efficiency, and its aprotic character means it dissolves salts and polar substrates without donating protons, which is why it is preferred where proton exchange would interfere with a reaction.
The solvent dissolves a very wide range of inorganic salts, organic compounds, polymers and gases, and it mixes freely with water, alcohols, ketones and aromatic solvents. Compared with other strong industrial solvents, it combines low volatility with comparatively low odour and easier handling.
Major Application Areas
Organic synthesis. It is a standard polar aprotic solvent and reaction medium, dissolving substrates that are poorly soluble elsewhere and supporting substitution, oxidation and coupling chemistry.
Pharmaceutical manufacture. It acts as a solvent and carrier in drug formulation and helps active ingredients penetrate biological tissue; it also appears in topical preparations.
Biochemical research. It is used as a solvent and cryoprotective additive in cell culture, protein purification and analytical work.
Cosmetics and health products. Its penetration-enhancing and moisturising behaviour brings it into some cosmetic and supplement formulations, always within the applicable regulatory limits.
Industrial processes. It serves as a solvent extractant, resin solvent, reaction diluent and lubricant additive in a range of manufacturing operations.
Handling, Storage and Quality Control
DMSO is hygroscopic; keep containers sealed and consider a dry nitrogen blanket where moisture-sensitive chemistry is involved.
It freezes at about 18.5 °C, close to normal room temperature, so winter shipments and unheated stores may arrive partly crystallised; warm gently and mix before use.
Store in a cool, dry, ventilated area away from strong oxidants, and keep it clear of ignition sources because it is combustible.
Use nitrile or butyl gloves and eye protection; the liquid readily carries dissolved substances through the skin.
Release each lot against gas chromatography purity, water content by Karl Fischer, colour and a UV absorbance check, since trace impurities show up strongly in spectroscopy and in cell culture work.
Frequently Asked Questions
Q: What is DMSO used for?
It is used as a polar aprotic solvent in organic synthesis, as a solvent and carrier in pharmaceutical and cosmetic formulation, as a cryoprotectant and solvent in biochemical research, and in industrial extraction and resin processing.
Q: What are the key physical properties of DMSO?
A boiling point of 189 °C, a melting point of 18.5 °C, a density near 1.10 g/cm3, a dielectric constant around 46.7 and complete miscibility with water and many organic solvents.
Q: Why is DMSO called a universal solvent?
Because it dissolves a very wide range of inorganic salts, organic compounds, polymers and gases while also mixing completely with water and with common organic solvents.
Q: Is DMSO hazardous?
It is a combustible, hygroscopic liquid of comparatively low volatility, but it penetrates skin easily and can carry dissolved substances with it, so gloves, eye protection and ventilation are required.
Q: How should DMSO be stored?
In a sealed container in a cool, dry, ventilated place away from strong oxidants and ignition sources; if it has crystallised, warm it gently and mix before use.
Q: Which purity grades are available?
Industrial and pharmaceutical grades are typically 99 percent or higher, and each lot should be backed by gas chromatography purity, Karl Fischer water content and UV absorbance data.