Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula (CH3)2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water. It penetrates the skin very readily, giving it the unusual property for many individuals of being secreted onto the surface of the tongue after contact with the skin and causing a garlic-like taste in the mouth.
Synthesis and production
It was first synthesized in 1866 by the Russian scientist Alexander Zaytsev, who reported his findings in 1867. Dimethyl sulfoxide is produced from dimethyl sulfide, a by-product of kraft pulping. It is industrially produced by oxidation of dimethyl sulfide with oxygen or nitrogen dioxide.
DMSO is a polar aprotic solvent and is less toxic than other members of this class, such as dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and HMPA. DMSO is frequently used as a solvent for chemical reactions involving salts, most notably Finkelstein reactions and other nucleophilic substitutions. It is also extensively used as an extractant in biochemistry and cell biology. Because DMSO is only weakly acidic, it tolerates relatively strong bases and as such has been extensively used in the study of carbanions. A set of non-aqueous pKa values (C-H, O-H, S-H and N-H acidities) for thousands of organic compounds have been determined in DMSO solution.
Because of its high boiling point, 189 °C (372 °F), DMSO evaporates slowly at normal atmospheric pressure. Samples dissolved in DMSO cannot be as easily recovered compared to other solvents, as it is very difficult to remove all traces of DMSO by conventional rotary evaporation, one technique to fully recover samples is removal of the organic solvent by evaporation followed by addition of water (to dissolve DMSO) and lyophilisation to remove both DMSO and water. Reactions conducted in DMSO are often diluted with water to precipitate or phase-separate products. The relatively high freezing point of DMSO, 18.5 °C (65.3 °F), means that at, or just below, room temperature it is a solid, which can limit its utility in some chemical processes (e.g. crystallization with cooling).
In its deuterated form (DMSO-d6), it is a useful but expensive solvent for NMR spectroscopy, again due to its ability to dissolve a wide range of analytes, its own simple spectrum, and its suitability for high-temperature NMR spectroscopic studies. Disadvantages to the use of DMSO-d6 are its high viscosity, which broadens signals, and its hygroscopicity, which leads to an overwhelming H2O resonance in the 1H NMR spectrum. It is often mixed with CDCl3 or CD2Cl2 for lower viscosity and melting points.
DMSO is finding increased use in manufacturing processes to produce microelectronic devices. It is widely used to strip photoresist in TFT-LCD 'flat panel' displays and advanced packaging applications (such as wafer-level packaging / solder bump patterning). It also used in biopreservation especially stem cell banking. DMSO is an effective paint stripper, being safer than many of the others such as nitromethane and dichloromethane.
The sulfur center in DMSO is nucleophilic toward soft electrophiles and the oxygen is nucleophilic toward hard electrophiles. The methyl groups of DMSO are somewhat acidic in character (pKa=35) due to the stabilization of the resultant carbanion by the S(O)R group, and so are deprotonated with strong bases like lithium diisopropylamide and sodium hydride. The sodium salt of DMSO formed in this way (sometimes referred to as "dimsyl sodium") is a useful base, e.g. it is often used for the deprotonation of ketones to form sodium enolates, phosphonium salts to form Wittig reagents, and formamidinium salts to form diaminocarbenes.
- (CH3)2SO + CH3I → [(CH3)3SO]I
- [(CH3)3SO]I + NaH → [(CH3)2CH2SO + NaI + H2
DMSO is used in PCR to inhibit secondary structures in the DNA template or the DNA primers. It is added to the PCR mix before reacting, where it interferes with the self-complementarity of the DNA, minimizing interfering reactions.
DMSO may also be used as a cryoprotectant, added to cell media to reduce ice formation and thereby prevent cell death during the freezing process. Approximately 10% may be used with a slow-freeze method, and the cells may be frozen at −80 °C or stored in liquid nitrogen safely.
In cell culture, DMSO is used to induce differentiation of P19 embryonic carcinoma cells into cardiomyocytes and skeletal muscle cells.
Use of DMSO in medicine dates from around 1963, when an Oregon Health & Science University Medical School team, headed by Stanley Jacob, discovered it could penetrate the skin and other membranes without damaging them and could carry other compounds into a biological system. In medicine, DMSO is predominantly used as a topical analgesic, a vehicle for topical application of pharmaceuticals, as an anti-inflammatory, and an antioxidant. Because DMSO increases the rate of absorption of some compounds through organic tissues, including skin, it can be used as a drug delivery system. It is frequently compounded with antifungal medications, enabling them to penetrate not just skin but also toe and fingernails.
In cryobiology DMSO has been used as a cryoprotectant and is still an important constituent of cryoprotectant vitrification mixtures used to preserve organs, tissues, and cell suspensions. Without it, up to 90% of frozen cells will become inactive. It is particularly important in the freezing and long-term storage of embryonic stem cells and hematopoietic stem cells, which are often frozen in a mixture of 10% DMSO, Media and 30% fetal bovine serum. In the cryogenic freezing of heteroploid cell lines (MDCK, VERO, etc.) a mixture of 10% DMSO with 90% EMEM (70% EMEM + 30% fetal bovine serum + antibiotic mixture) is used. As part of an autologous bone marrow transplant the DMSO is re-infused along with the patient's own hematopoietic stem cells.
In a 1978 study at the Cleveland Clinic Foundation in Cleveland, Ohio, researchers concluded that DMSO brought significant relief to the majority of the 213 patients with inflammatory genitourinary disorders that were studied. They recommended DMSO for all inflammatory conditions not caused by infection or tumor in which symptoms were severe or patients failed to respond to conventional therapy.
DMSO has been examined for the treatment of numerous conditions and ailments, but the U.S. Food and Drug Administration (FDA) has approved its use only for the symptomatic relief of patients with interstitial cystitis.
In medical research, DMSO is often used as a drug vehicle in in vivo and in vitro experiments. However, when a researcher is unaware of its pleiotrophic effects, or when the control groups are not carefully planned, a bias can occur; an effect of DMSO can be falsely attributed to the drug. For example, even a very low dose of DMSO has a powerful protective effect against acetaminophen induced liver injury in mice.
DMSO is metabolized to dimethyl sulfide and dimethyl sulfone. It is subject to renal and pulmonary excretion. A possible side effect of DMSO is therefore dimethylsulfidemia, which may cause a related blood borne halitosis symptom.
DMSO is marketed as an alternative medicine via books with titles such as DMSO: Nature's healer. Its popularity as an alternative cure is stated to stem from a 60 Minutes documentary featuring an early proponent. It is listed by the U.S. FDA as a fake cancer cure and the FDA has had a "running battle" with distributors. This has included Mildred Miller who promoted DMSO for a variety of disorders including arthritis, mental illness, emphysema, and cancer and wrote a book touting DMSO entitled A Little Dab Will Do Ya! (Quality Advertising, 1981). It is still listed as an ineffective alternative cancer cure by the American Cancer Society; for most conditions there is insufficient evidence to state any effect and most sources agree that its history of side effects when tested indicates caution when using it as a dietary supplement, for which it is heavily marketed with the usual disclaimer.
As is common in alternative medicine, promotion is based on early results which are not balanced by comprehensive tests of efficacy and safety. In arthritis, for example, controlled studies have yielded conflicting results and there are few human studies and significant known side effects.
DMSO is commonly used in veterinary medicine as a liniment for horses, alone or in combination with other ingredients. In the latter case, often, the intended function of the DMSO is as a solvent, to carry the other ingredients across the skin. Also in horses, DMSO is used intravenously, again alone or in combination with other drugs. It is used alone for the treatment of increased intracranial pressure and/or cerebral edema in horses.
Early clinical trials with DMSO were stopped because of questions about its safety, especially its ability to harm the eye. The most commonly reported side effects include headaches and burning and itching on contact with the skin. Strong allergic reactions have been reported.[full citation needed] In high concentrations, DMSO can be fatal to humans.[full citation needed] Industrial-grade DMSO is sometimes contaminated with other substances. DMSO can cause contaminants, toxins, and medicines to be absorbed through the skin, which may cause unexpected effects. DMSO is thought to increase the effects of blood thinners, steroids, heart medicines, sedatives, and other drugs. In some cases this could be harmful or dangerous. It is a developmental neurotoxin.
Because DMSO easily penetrates the skin, substances dissolved in DMSO may be quickly absorbed. Glove selection is important when working with DMSO. Thick rubber gloves are recommended. Nitrile gloves, which are very commonly used in chemical laboratories, have been found to dissolve rapidly with exposure to DMSO.
On September 9, 1965, the Wall Street Journal reported that a manufacturer of the chemical warned that the death of an Irish woman after undergoing DMSO treatment for a sprained wrist may have been due to the treatment, although no autopsy was done, nor was a causal relationship established.Clinical research using DMSO was halted and did not begin again until the National Academy of Sciences (NAS) published findings in favor of DMSO in 1972. In 1978, the US FDA approved DMSO for treating interstitial cystitis. In 1980, the US Congress held hearings on claims that the FDA was slow in approving DMSO for other medical uses. In 2007, the US FDA granted "fast track" designation on clinical studies of DMSO's use in reducing brain tissue swelling following traumatic brain injury. DMSO exposure to developing mouse brains can produce brain degeneration. This neurotoxicity could be detected at doses as low as 0.3 mL/kg, a level exceeded in children exposed to DMSO during certain medical treatments.
DMSO disposed into sewers can also cause odor problems in municipal effluents: waste water bacteria transform DMSO under hypoxic (anoxic) conditions into dimethyl sulfide (DMS) that has a strong disagreeable odor, similar to rotten cabbage. However, chemically pure DMSO is odorless because of the lack of C-S-C (sulfide) and C-S-H (mercaptan) linkages. Deodorization of DMSO is achieved by removing the odorous impurities it contains.
DMSO can decompose at the boiling temperature of 189 °C at normal pressure, possibly leading to an explosion. The decomposition is catalyzed by acids and bases and therefore can be relevant at even lower temperatures. A strong to explosive reaction also takes place in combination with halogen compounds, metal nitrides, metal perchlorates, sodium hydride, periodic acid and fluorinating agents.[full citation needed]
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