From Wikipedia, the free encyclopedia
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 has a
relatively high boiling point. DMSO has the unusual property that many
individuals perceive a garlic-like taste in the mouth after contact with the skin.
In terms of chemical structure, the molecule has idealized Cs symmetry. It has a trigonal pyramidal molecular geometry consistent with other three-coordinate S(IV) compounds, with a nonbonded electron pair on the approximately tetrahedral sulfur atom.
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 industrially from dimethyl sulfide, a by-product of the Kraft process, by oxidation with oxygen or nitrogen dioxide.
Reactions
Reactions with electrophiles
The sulfur center in DMSO is nucleophilic toward soft electrophiles and the oxygen is nucleophilic toward hard electrophiles. With methyl iodide it forms trimethylsulfoxonium iodide, [(CH3)3SO]I:
- (CH3)2SO + CH3I → [(CH3)3SO]I
This salt can be deprotonated with sodium hydride to form the sulfur ylide:
- [(CH3)3SO]I + NaH → (CH3)2S(CH2)O + NaI + H2
Acidity
The methyl groups of DMSO are only weakly acidic, with a pKa = 35. For this reason, the basicities of many weakly basic organic compounds have been examined in this solvent.
Deprotonation of DMSO requires strong bases like lithium diisopropylamide and sodium hydride. Stabilization of the resultant carbanion is provided by the S(O)R group. The sodium derivative of DMSO formed in this way is referred to as dimsyl sodium. It is a base, e.g., for the deprotonation of ketones to form sodium enolates, phosphonium salts to form Wittig reagents, and formamidinium salts to form diaminocarbenes. It is also a potent nucleophile.
Oxidant
In organic synthesis, DMSO is used as a mild oxidant, as illustrated by the Pfitzner–Moffatt oxidation and the Swern oxidation.
Ligand and Lewis base
Related to its ability to dissolve many salts, DMSO is a common ligand in coordination chemistry. Illustrative is the complex dichlorotetrakis(dimethyl sulfoxide)ruthenium(II) (RuCl2(dmso)4). In this complex, three DMSO ligands are bonded to ruthenium through sulfur. The fourth DMSO is bonded through oxygen. In general, the oxygen-bonded mode is more common.
In carbon tetrachloride solutions DMSO functions as a Lewis base with a variety Lewis acids such as I2, phenols, trimethyltin chloride, metalloporphyrins, and the dimer Rh2Cl2(CO)4. The donor properties are discussed in the ECW model. The relative donor strength of DMSO toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots.
Applications
Solvent
Distillation of DMSO requires a partial vacuum to achieve a lower boiling point.
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 cryodesiccation
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 solvent for NMR
spectroscopy, again due to its ability to dissolve a wide range of
analytes, the simplicity of its own 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 used as a solvent in in vitro and in vivo drug testing.
DMSO is also used to dissolve test compounds in in vitro drug discovery and drug design screening programs (including high-throughput screening programs). This is because it able to dissolve both polar and nonpolar compounds, can be used to maintain stock solutions of test compounds (important when working with a large chemical library), is readily miscible with water and cell culture media,
and has a high boiling point (this improves the accuracy of test
compound concentrations by reducing room temperature evaporation). One limitation with DMSO is that it can affect cell line
growth and viability (with low DMSO concentrations sometimes
stimulating cell growth, and high DMSO concentrations sometimes
inhibiting or killing cells).
DMSO is used as a vehicle in in vivo studies of test compounds too. It has, for example, been employed as a co-solvent to assist absorption of the flavonol glycoside Icariin in the nematode worm Caenorhabditis elegans. As with its use in in vitro studies, DMSO has some limitations in animal models. Pleiotropic
effects can occur and, if DMSO control groups are not carefully
planned, then solvent effects can falsely be attributed to the
prospective drug. For example, even a very low dose of DMSO has a powerful protective effect against paracetamol (acetaminophen)-induced liver injury in mice.
In addition to the above, 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). DMSO is an effective paint stripper too, being safer than many of the others such as nitromethane and dichloromethane.
Biology
DMSO is used in polymerase chain reaction (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 in a PCR reaction is applicable for supercoiled plasmids (to relax before amplification) or DNA templates with high GC-content (to decrease thermostability).
For example, 10% final concentration of DMSO in the PCR mixture with
Phusion decreases primer annealing temperature (i.e. primer melting
temperature) by 5.5–6.0 °C (9.9–10.8 °F).
It is well known as a reversible cell cycle arrester at phase G1 of human lymphoid cells.
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 (−112 °F) 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.
Medicine
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 biological tissues, including skin, it is used in some transdermal drug delivery systems. Its effect may be enhanced with the addition of EDTA.
It is frequently compounded with antifungal medications, enabling them
to penetrate not just skin but also toenails and fingernails.
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. A 1978 study concluded that DMSO brought significant relief to the majority of the 213 patients with inflammatory genitourinary disorders that were studied.
The authors recommended DMSO for genitourinary inflammatory conditions
not caused by infection or tumor in which symptoms were severe or
patients failed to respond to conventional therapy.
A gel containing DMSO, dexpanthenol, and heparin, is sold in Germany and eastern Europe (commercialized under the Dolobene brand) for topical use in sprains, tendinitis, and local inflammation.
In interventional radiology, DMSO is used as a solvent for ethylene vinyl alcohol in the Onyx liquid embolic agent, which is used in embolization, the therapeutic occlusion of blood vessels.
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, a freezing medium, 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.
DMSO is metabolized by disproportionation to dimethyl sulfide and dimethyl sulfone.
It is subject to renal and pulmonary excretion. A possible side effect
of DMSO is therefore elevated blood dimethyl sulfide, which may cause a
blood borne halitosis symptom.
Alternative medicine
DMSO is marketed as an alternative medicine. Its popularity as an alternative cure is stated to stem from a 60 Minutes documentary featuring an early proponent. However, DMSO is an ingredient in some products listed by the U.S. FDA as fake cancer cures and the FDA has had a running battle with distributors. One such distributor is Mildred Miller, who promoted DMSO for a variety of disorders and was consequently convicted of Medicare fraud.
The use of DMSO as an alternative treatment for cancer is of
particular concern, as it has been shown to interfere with a variety of chemotherapy drugs, including cisplatin, carboplatin, and oxaliplatin. There is insufficient evidence to support the hypothesis that DMSO has any effect,
and most sources agree that its history of side effects when tested
warrants caution when using it as a dietary supplement, for which it is
marketed heavily with the usual disclaimer.
Veterinary medicine
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.
Taste
The perceived garlic taste upon skin contact with DMSO may be due to nonolfactory activation of TRPA1 receptors in trigeminal ganglia. Unlike dimethyl and diallyl disulfide (also with odors resembling garlic), the mono- and tri- sulfides (typically with foul odors), and other similar structures, the pure chemical DMSO is odorless.
Safety
Toxicity
DMSO is a non-toxic solvent with a median lethal dose higher than ethanol (DMSO: LD50, oral, rat, 14,500 mg/kg; ethanol: LD50, oral, rat, 7,060 mg/kg).
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.
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.
In Australia, it is listed as a Schedule 4 (S4) Drug, and a company has been prosecuted for adding it to products as a preservative.
Because DMSO easily penetrates the skin, substances dissolved in DMSO may be quickly absorbed. Glove selection is important when working with DMSO. Butyl rubber, fluoroelastomer, neoprene, or thick (15 mil / 0.4 mm) latex gloves are recommended. Nitrile
gloves, which are very commonly used in chemical laboratories, may
protect from brief contact but have been found to degrade 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 bone marrow transplant.
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.
Explosion hazard
Dimethyl sulfoxide can produce an explosive reaction when exposed to acyl chlorides; at a low temperature, this reaction produces the oxidant for Swern oxidation.
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.
