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Short answer: dimethyl sulfoxide (DMSO) boils at about 189 °C at 760 mmHg (standard pressure), according to the Merck Index as cited in PubChem and to ILO-WHO ICSC card 0459. It freezes at about 18.5 °C, so it is a solid in a cool lab or refrigerator, and its vapor pressure at room temperature is very low.
This page is a lab-solvent reference card for DMSO (CAS 67-68-5, C2H6OS). It lists the physical properties researchers look up most often, shows how much the published values differ between sources, and explains what each number means at the bench. For the molecular weight and mole conversions, see DMSO molar mass. The same format is used for DMF boiling point and physical properties.
Definition and scope
DMSO is a polar, water-miscible organic liquid used as a solvent and as a vehicle in cell-culture and cryopreservation work. The values below are taken from two openly readable references, read on 2026-11-08: the PubChem compound record for DMSO (CID 679), which compiles experimental properties from the Merck Index, HSDB, CAMEO Chemicals and other handbooks, and the ILO-WHO International Chemical Safety Card (ICSC) 0459. Where a handbook gives a different figure, the table says so rather than choosing silently.
DMSO physical properties at a glance
| Property | Reported value | Source and conditions |
|---|---|---|
| Boiling point | 189 °C (372 °F) | Merck Index 2013 (via HSDB), ICSC 0459, US DOE PAC; 760 mmHg |
| Freezing / melting point | 18.5 °C | ICSC 0459 and NTP 1992; Merck Index 2013 gives 18.45 °C and US DOE PAC gives 17.89 °C |
| Density | 1.100 g/mL | Merck Index 2013, 20/4 °C; US DOE PAC gives 1.101 at 25 °C |
| Vapor pressure | 0.42 mmHg (about 56 Pa) at 20 °C; 0.60 mmHg at 25 °C | HSDB (Verschueren; Daubert and Danner); ICSC 0459 gives 59.4 Pa at 20 °C |
| Viscosity | 2.47 cP at 20 °C | Merck Index 2013; ICSC 0459 gives kinematic viscosity 1.95 mm2/s at 20 °C |
| Refractive index | 1.4783 (20 °C, D line) | Merck Index 2013; Lide 1994 gives 1.4770 |
| Dielectric constant | 45 | Merck Index 2013 via HSDB (a single compiled value) |
| pKa | 35.1 | Willer, cited in HSDB (Kirk-Othmer) |
| Miscibility with water | Miscible | ICSC 0459 |
| Flash point | 87 °C closed cup; 95 °C open cup | ICSC 0459 (closed cup); NFPA via HSDB (open cup) |
How the numbers are used in practice
DMSO boiling point
The boiling point of 189 °C is consistent across the Merck Index, ICSC and the US DOE protective action criteria data. It is much higher than common volatile solvents. Editorial interpretation: because of this, DMSO is not removed by an ordinary rotary-evaporator run the way ethyl acetate or dichloromethane are, which is why extraction workflows often wash it out with water (it is water-miscible) instead of evaporating it.
DMSO freezing point
At 18.5 °C, pure DMSO freezes just below typical room temperature. Editorial interpretation: a bottle stored in a refrigerator or a cold room will be solid, and stock should be fully thawed and mixed before it is pipetted. Mixtures with water or other components freeze at different temperatures; the values here apply to the pure liquid. See cryopreservation media for how DMSO is used in freezing media.
DMSO vapor pressure
The vapor pressure is about 0.42 mmHg at 20 °C and 0.60 mmHg at 25 °C, which is low. The two figures differ because they are at different temperatures, not because the sources disagree. Editorial interpretation: open containers lose little solvent to evaporation at room temperature, compared with volatile solvents.
DMSO density and viscosity
Density is about 1.10 g/mL, so DMSO is denser than water. The two viscosity figures use different units: 2.47 cP is dynamic viscosity (Merck Index), while 1.95 mm2/s is kinematic viscosity (ICSC). Dividing dynamic viscosity by density gives roughly 2.25 mm2/s, so the entries are close but not identical, and the sources should not be treated as identical measurements.
DMSO polarity, dielectric constant and miscibility
The compiled dielectric constant is 45, and DMSO is miscible with water. These are the sourced polarity-related facts; no polarity-index figure was found in the sources read for this page, so none is given here.
DMSO refractive index and pKa
The refractive index is 1.4783 at 20 °C (Merck Index, 2013) or 1.4770 (Lide, 1994). The reported pKa of 35.1 describes DMSO as an extremely weak acid and is a reference value rather than a figure relevant to aqueous buffer work.
Where it matters for lab decisions
- Solvent removal: a 189 °C boiling point is the main reason DMSO is treated as a hard-to-evaporate solvent. See green chemistry in the lab for solvent-selection context.
- Storage and handling: ICSC 0459 classifies DMSO as a combustible liquid (GHS signal word: Warning) with a closed-cup flash point of 87 °C. Check the flash-point method in any safety data sheet you compare, because closed-cup and open-cup values differ.
- Gloves: glove choice for chemical work is covered in nitrile gloves and chemical resistance.
Common misunderstandings
- Sources disagree on the boiling point. They largely do not: 189 °C appears in the Merck Index, ICSC and DOE data. The visible spread is in the freezing point (17.89 to 18.5 °C), vapor pressure (different temperatures) and viscosity (different units).
- Boiling point is the same at every pressure. The 189 °C value is for 760 mmHg; boiling points fall under vacuum.
- A high boiling point means it is not flammable. ICSC lists DMSO as a combustible liquid.
FAQ
What is the boiling point of DMSO?
About 189 °C (372 °F) at 760 mmHg.
What is the freezing point of DMSO?
About 18.5 °C for the pure liquid (ICSC); other handbooks report 18.45 and 17.89 °C.
What is the density of DMSO?
1.100 g/mL at 20 °C (Merck Index, 2013).
What is the vapor pressure of DMSO?
0.42 mmHg at 20 °C and 0.60 mmHg at 25 °C.
Is DMSO miscible with water?
Yes, ICSC 0459 lists it as miscible.
What is the dielectric constant of DMSO?
45, as a compiled value in HSDB citing the Merck Index.
What is the pKa of DMSO?
35.1 as reported by Willer in HSDB.
Sources
- PubChem, Dimethyl sulfoxide, CID 679 (boiling point and experimental properties sections): pubchem.ncbi.nlm.nih.gov/compound/679. Read 2026-11-08.
- ILO-WHO International Chemical Safety Card 0459, Dimethyl sulfoxide: chemicalsafety.ilo.org, ICSC 0459. Read 2026-11-08.
