Dimethyl Sulfoxide
Properties
| State | Liquid at room temperature |
| Color | Colorless |
| Solubility | Miscible with water and most organic solvents |
| Melting Point | 19 °C |
| Boiling Point | 189 °C |
About Dimethyl Sulfoxide
DMSO is the most distinctive aprotic solvent in routine use, and almost everything strange about it traces back to the S=O group. The sulfur is sp3 with one lone pair, the S-O bond has substantial ionic character, and the dipole moment is 3.96 D — bigger than water's. That gives DMSO a dielectric constant of 47 and the ability to solvate cations very strongly while leaving anions naked. The result: SN2 reactions in DMSO can run 10⁹ times faster than the same reaction in methanol because the nucleophile is unencumbered by hydrogen-bond solvation. DMSO is also a competent oxidant — the Swern oxidation activates DMSO with oxalyl chloride at -78 °C to convert primary alcohols to aldehydes and secondary alcohols to ketones via an alkoxysulfonium intermediate, with dimethyl sulfide and CO/CO2 as byproducts. The Pfitzner-Moffatt and Parikh-Doering oxidations use DCC and SO3·pyridine respectively to do the same chemistry. In biology, DMSO is the standard cryoprotectant for cell stocks — 5-10% v/v added to serum-containing media before freezing prevents intracellular ice formation by binding water tightly and depressing the freezing point. Mammalian cell culture, sperm banking, and stem cell storage all run on DMSO/glycerol cryomixes. The famous skin penetration: DMSO's small size and amphiphilicity let it slip through the stratum corneum within minutes, taking dissolved solutes along for the ride. That makes it a useful drug-delivery research tool and a serious contamination hazard — pure DMSO is usually fine, DMSO with a dissolved compound on your glove is not. The garlic-breath effect comes from skin-absorbed DMSO being reduced in vivo to dimethyl sulfide.
Where you'll encounter it
If you have ever pulled a vial of HEK293 or HeLa cells out of a -80 °C freezer or LN2 dewar, the cloudy liquid you thaw is 90% medium and 10% DMSO. In a med-chem lab, DMSO is the solvent for compound libraries — every commercial library plate ships dissolved in DMSO at 10 mM, and DMSO is the carrier in nearly every IC50 dose-response curve. The Swern oxidation is the textbook small-scale alcohol-to-ketone conversion when you cannot stomach the chromium of a Jones or PCC oxidation, though you pay for it in the dimethyl-sulfide stench during workup.
Common Uses
- Cryoprotectant in mammalian cell culture freezing media at 5-10 percent v/v with serum-containing medium
- Compound storage solvent for screening libraries at 10 mM in 96- or 384-well master plates
- Polar aprotic reaction solvent for SN2 alkylations, eliminations, and anionic nucleophile chemistry
- Oxidant in the Swern oxidation with oxalyl chloride at -78 °C to convert alcohols to aldehydes and ketones
- Vehicle solvent in dose-response pharmacology assays at 0.1-1 percent final concentration in cell media
- FDA-approved instillation therapy for interstitial cystitis as a 50 percent aqueous bladder rinse (RIMSO-50)
- Veterinary topical anti-inflammatory for musculoskeletal injuries in racehorses and large animals
- Industrial extractant in aromatic-aliphatic separations and as a paint stripper substitute for harsher solvents
Safety Information
Low acute toxicity itself — oral LD50 in rats is around 14,500 mg/kg. The dominant hazard is its skin permeability: DMSO crosses the stratum corneum within minutes and carries any dissolved solute with it, which means a contaminated glove or sleeve becomes a transdermal injection of whatever else was in solution. Treat any spill on PPE as PPE you change immediately, and never use DMSO to dissolve anything you would not want absorbed. No OSHA PEL or ACGIH TLV has been established. GHS classifications are limited (H315 mild skin irritation, H319 mild eye irritation in some assessments). Practical handling rules: use butyl-rubber gloves rather than nitrile (DMSO permeates standard nitrile in under 30 minutes), work in a fume hood, keep DMSO bottles closed (it is hygroscopic and will pick up ~10% water on extended exposure to humid air), and accept that you will taste garlic for the rest of the afternoon if you get any on your hands.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.