Dimethyl sulfoxide

Dimethyl sulfoxide, commonly known as DMSO, is a colorless liquid that serves as a vital organosulfur compound in science. It is classified as a polar aprotic solvent, which means it possesses a dipole moment but lacks an oxidizable hydrogen atom bonded to an electronegative element. This unique chemical property allows DMSO to dissolve both polar and nonpolar compounds. It is also miscible, or easily mixable, with water and a wide variety of organic solvents. Because it can dissolve so many different substances, it is a fundamental tool in chemistry, biology, and medicine.

At the molecular level, DMSO has a specific structure known as trigonal pyramidal geometry. The sulfur atom sits at the center and is approximately tetrahedral, meaning it is bonded to three groups while holding a nonbonded electron pair. This arrangement gives the molecule idealized Cs symmetry. In chemical reactions, the sulfur center acts as a nucleophile toward soft electrophiles, while the oxygen atom acts as a nucleophile toward hard electrophiles. These specific interactions allow scientists to use DMSO to build complex molecules through various chemical pathways.

DMSO can function in several distinct chemical roles depending on the environment. It acts as a mild oxidant in organic synthesis, forming the basis for specialized reactions like the Swern, Pfitzner–Moffatt, and Corey–Kim oxidations. In these processes, DMSO helps create intermediate sulfonium species. Additionally, it serves as a common ligand in coordination chemistry. A ligand is a molecule that binds to a central metal atom. For example, in the complex dichlorotetrakis(dimethyl sulfoxide)ruthenium(II), three DMSO ligands bond to the ruthenium through sulfur, while a fourth bonds through oxygen.

The history of DMSO began in the mid-19th century. The Russian scientist Alexander Zaytsev first synthesized the compound in 1866 and reported his findings a year later. While it was known in labs, its modern industrial use grew through the work of Thor Smedslund at the Stepan Chemical Company. Industrially, DMSO is produced from dimethyl sulfide, which is a by-product of the kraft process. This is achieved through oxidation using either oxygen or nitrogen dioxide. This transition from a laboratory curiosity to an industrial staple changed how many chemical processes are managed today.

In biological and medical settings, DMSO is highly significant due to its ability to penetrate membranes. In 1963, a team at Oregon Health & Science University led by Stanley Jacob discovered that DMSO could pass through skin and biological membranes without causing damage. This makes it an excellent vehicle to carry other drugs into the body. For instance, the FDA-approved medication PENNSAID uses a 45.5% DMSO vehicle to help the drug diclofenac penetrate the skin. However, users should note that absorbing DMSO through the skin can lead to a garlic-like taste in the mouth as the body metabolizes it.

DMSO also plays a critical role in cryobiology, the study of freezing organisms. It acts as a cryoprotectant, which is a substance used to protect cells from damage during freezing. Without a cryoprotectant, up to 90% of frozen cells can become inactive. When storing embryonic or hematopoietic stem cells, scientists often use a mixture containing 10% DMSO. This helps prevent the formation of ice crystals that would otherwise kill the cells. In the field of genetics, DMSO is also used in the polymerase chain reaction (PCR) to prevent DNA from forming interfering secondary structures.

Despite its many uses, DMSO has specific limitations and risks. It has a high boiling point, which means it evaporates very slowly at normal atmospheric pressure. To remove it during distillation, scientists must use a partial vacuum

. In medical research, high concentrations of DMSO can sometimes inhibit or kill cells, while very low concentrations might stimulate growth. Furthermore, while it is popular in alternative medicine, there is insufficient evidence to support its use as a cancer treatment. In fact, DMSO can interfere with certain chemotherapy drugs like cisplatin and oxaliplatin, making its use in those contexts a matter of great caution.