Dimethyl sulfoxide (DMSO) is a sulfur-containing organic compound with the molecular formula C2H6OS and CAS number 67-68-5. It is one of the most versatile solvents in industrial and laboratory chemistry and is often called the universal solvent because it dissolves a remarkably wide range of polar and nonpolar substances. This article reviews the physical properties, chemical properties, and common synthesis methods of DMSO.
Physical Properties of DMSO
At room temperature, DMSO is a colorless, odorless, transparent liquid with strong hygroscopicity. Its key physical properties are summarized below.
| Property | Value |
|---|---|
| Appearance | Colorless, odorless transparent liquid |
| Melting Point | 18.4 °C |
| Boiling Point | 189 °C |
| Density at 20 °C | 1.100 g/cm3 |
| Flash Point | 95 °C |
| Solubility | Miscible with water, ethanol, acetone, ethyl acetate, pyridine, and many other organic solvents |
Because DMSO is a highly polar aprotic solvent, it dissolves both water-soluble and many water-insoluble compounds. It is miscible with water in all proportions and can penetrate many materials, including some types of skin, which requires careful handling in the laboratory.
Chemical Properties of DMSO
DMSO is relatively stable at room temperature but can decompose when exposed to high temperatures, strong sunlight, or oxygen. When heated in the presence of acids, it may produce small amounts of methyl mercaptan, formaldehyde, dimethyl sulfide, and methanesulfonic acid. It reacts vigorously with strong oxidizing agents and certain chlorinating agents, and it burns with a pale blue flame in air. DMSO can be reduced to dimethyl sulfide and, under strong oxidizing conditions, oxidized to dimethyl sulfone. These redox characteristics are exploited in organic synthesis, where DMSO serves as a mild oxidant and as a reaction medium for many transformations.
Synthesis Methods of DMSO
DMSO can be produced industrially by several routes.
Methanol-carbon disulfide method: methanol and carbon disulfide are used as raw materials and oxidized to produce DMSO.
Hydrogen peroxide method: dimethyl sulfide reacts with hydrogen peroxide in acetone as a buffer to form DMSO.
Nitrogen dioxide method: dimethyl sulfide is first generated from methanol and hydrogen sulfide, then oxidized with nitrogen dioxide to produce DMSO.
In commercial practice, DMSO is most often produced by oxidizing dimethyl sulfide, which is obtained as a by-product of the kraft pulping process or synthesized from methanol and hydrogen sulfide.
Applications Related to the Properties of DMSO
The unique properties of DMSO support a broad range of applications. In the pharmaceutical industry, DMSO is used as a solvent and penetration enhancer in topical formulations. In polymer processing, it dissolves polyacrylonitrile and other difficult polymers for fiber spinning. In electronics, it is used as a stripping and cleaning solvent. In analytical chemistry, it is a standard NMR solvent because of its ability to dissolve a wide range of samples. Its high boiling point and thermal stability also make it suitable for high-temperature reactions.
Safety and Handling of DMSO
Although DMSO has low acute toxicity, it penetrates the skin rapidly and can carry dissolved substances into the body, so gloves that are resistant to DMSO should be used. It is hygroscopic and should be stored in tightly sealed containers protected from moisture. Because DMSO is combustible, it must be kept away from open flames and strong oxidizers. Waste DMSO should be collected separately and disposed of according to local regulations.
Frequently Asked Questions
What is the CAS number of DMSO?
Dimethyl sulfoxide has the CAS number 67-68-5, the molecular formula C2H6OS, and a molecular weight of 78.13 g/mol.
What is the density of DMSO?
The density of DMSO is approximately 1.100 g/cm3 at 20 °C, which is slightly higher than that of water. This value is important for calculating reaction volumes and mixture compositions.
Is DMSO soluble in water?
Yes. DMSO is miscible with water in all proportions. It also dissolves in ethanol, acetone, ethyl acetate, pyridine, and many other organic solvents, which is why it is called a universal solvent.
Does DMSO decompose easily?
DMSO is stable at room temperature but can decompose when heated strongly or exposed to oxygen and light for long periods. Contact with strong acids can generate methyl mercaptan, formaldehyde, and other decomposition products.
Why is DMSO used as an NMR solvent?
Deuterated DMSO, DMSO-d6, dissolves a wide range of organic and inorganic samples, and its relatively high boiling point allows measurements at elevated temperature. It is one of the most commonly used solvents in proton NMR analysis.
Can DMSO penetrate the skin?
Yes. DMSO is absorbed rapidly through intact skin and can carry other dissolved chemicals with it. Protective gloves that resist DMSO penetration should be worn when handling solutions that contain dissolved toxic substances.
