Understanding Dimethyl Sulfoxide: Properties, Synthesis, and Benefits
What is Dimethyl Sulfoxide?
Dimethyl sulfoxide is an organosulfur compound which has two methyl groups, one oxygen atom and one sulfur atom. Chemical formula of dimethyl sulfoxide is (CH3)2SO. It is a colorless liquid which has the ability to dissolve both polar and non - polar compounds. It is also known as DMSO (abbreviation of dimethyl sulfoxide). It is known by other names as well such as methylsulfinylmethane or methyl sulfoxide etc.
Formula of Dimethyl Sulfoxide
Structure of Dimethyl Sulfoxide
Dimethyl sulfoxide is a polar aprotic compound. It has idealized Cs symmetry. It has a trigonal pyramidal molecular geometry. In dimethyl sulfoxide, S=O bond length is 167.8 pm and S-C bond length is 186.2 pm. O-S-C bond angle is 105.1° and C-S-C bond angle is 98°.
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The sulfur atom in dimethyl sulfoxide has a non bonded electron pair.
Properties of Dimethyl Sulfoxide
It shows following physical and chemical properties –
Its molar mass is 78.13 g/mol.
It is a colorless liquid.
It is a polar aprotic solvent.
It can dissolve both polar and non - polar compounds.
It is soluble in many organic solvents. But not soluble in diethyl ether.
It is soluble in water as well.
Its density is 1.10 g/cm3
Its melting point is 19 °C.
Its boiling point is 189 °C.
It has a garlic like taste.
Reaction with electrophile – Dimethyl sulfoxide acts as a nucleophile and reacts with electrophiles. Its sulfur center acts as nucleophile for weak electrophiles while its oxygen center acts as nucleophile for strong electrophiles. For example, it reacts with methyl iodide and forms trimethylsulfoxonium iodide. Reaction is given below –
(CH3)2SO + CH3I → [(CH3)3SO]I
This reaction can be used to form sulfur ylide. When trimethylsulfoxonium iodide salt reacts with sodium hydride, it forms sulfur ylide. Reaction is given below –
[(CH3)3SO]I + NaH → (CH3)2S(CH2)O + NaI + H2
Dimethyl sulfoxide is a weakly acidic compound and shows reaction with base.
It acts as a mild oxidant. For example, in Swern oxidation reaction.
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It works as a common ligand in coordination chemistry. For example, [RuCl2(DMSO)4]. Its structure is given below –
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Synthesis of Dimethyl Sulfoxide
Dimethyl sulfoxide was first synthesized by the Russian Scientist Alexander Zaytsev in 1867. At industrial level, it is produced from dimethyl sulfide by oxidation with oxygen or nitrogen dioxide. It is a by – product of the Kraft process.
What is Dimethyl Sulfoxide Used for?
Due to its unique properties such as miscibility in organic solvents, polar aprotic solvent and less toxic nature, it is used in various fields for various purposes. Few of its applications are listed below –
It is a good solvent for polar and non non – polar organic and inorganic compounds. So, it is used in the synthesis of many compounds. It is used in the Finkelstein reactions and various nucleophilic reactions.
It is widely used as an extractant in cell biology and biochemistry.
Being a weak acid, it can tolerate strong bases, so it is used in the study of carbanions.
Acid dissociation constant can be determined for various organic compounds by using a DMSO solution.
Its solution is used in NMR – spectroscopy as well.
It can be used for manufacturing of microelectronic devices.
It is used in advanced packaging applications.
It is used in LCD – flat panel displays.
It is used in stem cell baking or biopreservation.
It is a safer option as paint stripper than nitromethane and dichloromethane.
It is used in drug design and sample management as it’s a good solvent and can dissolve various compounds.
Its biological uses include its usage as an inhibitor for DNA primers in polymerase chain reaction or PCR.
It acts as a reversible cell cycle arrester of human lymphoid cells.
It is used for protecting tissues from freezing damage. It is added into the cell media to reduce ice formation so that cells will not die due to over freezing.
It is used as co – solvent as well in many biological adsorption processes. For example, C. elegans nematode uses it for absorption of flavonol glycoside.
It has been used in medicines since 1963. It can enter into the cell, without damaging the cell membrane. It is used in analgesics, anti – inflammatory and antioxidant drugs.
It is used in the transdermal drug delivery systems.
It is one of the ingredients of antifungal medicines.
It is used as a drug vehicle in - in vitro and in vivo experiments.
It is used as a cryoprotectant.
It is used as an alternative medicine for treatment of many diseases. It is being used as an alternative medicine for the treatment of cancer as well.
It is used in the medicines used for treatment of skin related problems in horses.
Although it is widely used as a solvent, but it has a disadvantage that it is very difficult to remove DMSO completely. So, it becomes difficult to recover the samples dissolved in DMSO.
Dimethyl Sulfoxide: Summary in Tabular Form
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FAQs on Dimethyl Sulfoxide Explained: Formula, Structure & Applications
1. What is Dimethyl Sulfoxide (DMSO) and what is its chemical formula?
Dimethyl Sulfoxide, commonly known as DMSO, is an organosulfur compound with the chemical formula (CH₃)₂SO. It is a colourless liquid that is highly polar and miscible with a wide range of organic solvents as well as water. Its unique properties make it an extremely versatile aprotic solvent in both laboratory and industrial settings.
2. What are the primary applications of Dimethyl Sulfoxide in chemistry and medicine?
DMSO has several important applications, primarily due to its excellent solvent properties and ability to penetrate biological membranes. Key uses include:
- Chemical Solvent: It is widely used as a polar aprotic solvent, especially in organic reactions like nucleophilic substitutions (SN2 reactions) and polymer chemistry.
- Medical Treatment: It is used as a prescription medicine for treating interstitial cystitis (a bladder pain syndrome) and as a topical analgesic.
- Drug Delivery: Its ability to be absorbed through the skin allows it to be used as a vehicle to carry other drugs into the body.
- Cryoprotectant: DMSO is used to protect biological tissues and cells during cryopreservation (freezing).
3. How is the molecular structure of Dimethyl Sulfoxide (DMSO) described?
The molecular structure of DMSO features a sulfur atom bonded to two methyl groups (–CH₃) and one oxygen atom. The geometry around the sulfur atom is trigonal pyramidal, similar to ammonia. The molecule is highly polar because of the significant difference in electronegativity between the sulfur and oxygen atoms in the S=O bond, which gives the oxygen a partial negative charge and the sulfur a partial positive charge.
4. What are some important physical properties of DMSO?
Dimethyl Sulfoxide has distinct physical properties that contribute to its usefulness. Notable properties include:
- Appearance: It is a clear, colourless, and odourless to slightly garlic-like liquid.
- Boiling Point: It has a very high boiling point for its molecular weight, at 189 °C (372 °F), due to its high polarity.
- Freezing Point: It has a relatively high freezing point of 18.5 °C (65.3 °F), meaning it can solidify on a cool day.
- Miscibility: It is fully miscible with water and a broad range of organic solvents like alcohols, ethers, and ketones.
5. Why is DMSO classified as a polar aprotic solvent?
DMSO is classified as a polar aprotic solvent based on two key structural features. It is 'polar' because the sulfoxide group (S=O) creates a strong dipole moment in the molecule. It is 'aprotic' because it lacks acidic protons; it does not have any hydrogen atoms attached to highly electronegative atoms like oxygen or nitrogen. This combination allows it to dissolve many ionic compounds but prevents it from participating in hydrogen bonding as a proton donor, which is a critical characteristic for certain chemical reactions.
6. How does using DMSO as a solvent favour SN2 reactions over SN1 reactions?
DMSO specifically favours SN2 (bimolecular nucleophilic substitution) reactions because as a polar aprotic solvent, it effectively solvates cations but leaves anions (the nucleophiles) relatively 'naked' and highly reactive. This enhances the nucleophile's strength, speeding up the single-step SN2 mechanism. In contrast, SN1 reactions, which proceed through a carbocation intermediate, are favoured by polar protic solvents (like water or ethanol) that can stabilise both the cation and the leaving group anion through hydrogen bonding.
7. What is the difference between Dimethyl Sulfoxide (DMSO) and Dimethyl Sulfone (DMSO₂)?
The primary difference lies in the oxidation state of the sulfur atom. Dimethyl Sulfoxide (DMSO) has the formula (CH₃)₂SO, where the sulfur is bonded to one oxygen atom. Dimethyl Sulfone (DMSO₂), with the formula (CH₃)₂SO₂, is the fully oxidised form where the sulfur is bonded to two oxygen atoms. This structural difference makes DMSO₂ a solid at room temperature and chemically more inert than DMSO, and it is often used as a high-temperature polar solvent.
8. Is Dimethyl Sulfoxide (DMSO) safe for human use?
While DMSO is an FDA-approved medication for specific conditions, its safety depends on its purity and application. Pharmaceutical-grade DMSO is used for medical treatments under supervision. However, industrial-grade DMSO can contain harmful impurities. A key safety concern is its ability to be rapidly absorbed through the skin, potentially carrying toxic substances dissolved in it into the bloodstream. Common side effects include a garlic-like taste or breath and skin irritation.
9. What is the common industrial method for synthesizing Dimethyl Sulfoxide?
The most common industrial synthesis of Dimethyl Sulfoxide involves the oxidation of dimethyl sulfide ((CH₃)₂S). Dimethyl sulfide is a by-product of the Kraft process used in paper manufacturing. This oxidation is typically carried out using an oxidizing agent like oxygen in the presence of nitrogen oxides as a catalyst, or with other agents like hydrogen peroxide. The reaction converts the sulfide into a sulfoxide to produce DMSO.
