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[dubious – discuss] onto the surface of the tongue[citation needed] after contact with the skin and causing a garlic-like taste in the mouth,[2] but unlike dimethyl and diallyl disulfide (with odors resembling garlic), the mono- and tri- sulfides (typically disgusting), and similar structures, the pure chemical is odorless. Perceived garlic odor resulting from DMSO intake may be due to nonolfactory activation of TRPA1 receptors in trigeminal ganglia. [1]
Although it has some niche medicinal uses it also has significant known side effects. It has been discussed as treatment for cancer and other conditions.[3][4][2]
Synthesis and production
It was first synthesized in 1866 by the Russian scientist Alexander Zaytsev, who reported his findings in 1867.[5] 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.[6]
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:
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(CH3)2SO + CH3I → [(CH3)3SO]I
This salt can be deprotonated with sodium hydride to form the sulfur ylide:
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[(CH3)3SO]I + NaH → [(CH3)2CH2SO + 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,[12] as illustrated by the Pfitzner-Moffatt oxidation and the Swern oxidation.[13]
Ligand
Related to its ability to dissolve many salts, DMSO is a common ligand in coordination chemistry.[14] 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.
Applications
Biology
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.[15]
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.[16] 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.
DMSO has been used as a co-solvent to assist absorption of the flavonol glycoside Icariin into the C. elegans nematode worm.[17]
In cell culture, DMSO is used to induce differentiation of P19 embryonic carcinoma cells into cardiomyocytes and skeletal muscle cells.
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