⚗️ Complete Solvent Guide

What Is Sulfolane? A Complete Guide to the Dipolar Aprotic Solvent

Uses, Properties & Applications · CAS 126-33-0 · Tetramethylene Sulfone

If you work in petrochemical refining, electronics, gas treating, or pharmaceutical synthesis, you have almost certainly encountered sulfolane - even if you didn't know it by name. This colorless, oily liquid is one of the most versatile dipolar aprotic solvents in industry, valued for a rare combination of high polarity, outstanding thermal stability, and very low volatility. 🔬

In this complete guide, we explain exactly what sulfolane is, what makes its chemistry special, where it is used across major industries, how it stacks up against alternatives like NMP and DMSO, and how to source reliable material in bulk. For full specification data and a downloadable SDS, see our Sulfolane product page.

📑 Table of Contents

1. What Is Sulfolane?
2. Structure & Key Properties
3. Why Sulfolane Is Such a Useful Solvent
4. Major Uses & Applications
5. Sulfolane vs NMP vs DMSO
6. Grades & Sourcing
7. Safety at a Glance
8. Frequently Asked Questions

1. What Is Sulfolane? ⚗️

Sulfolane - also called tetramethylene sulfone or thiolane-1,1-dioxide - is an organosulfur compound with the chemical formula (CH₂)₄SO₂. It is classified as a cyclic sulfone: a five-membered carbon ring with a sulfur atom that is doubly bonded to two oxygen atoms.

It was originally developed by Shell Oil Company in the 1960s as a selective solvent to purify butadiene, and it quickly proved indispensable for separating aromatic hydrocarbons from refinery streams. Today it is produced worldwide and supplied in both industrial and high-purity electronic-grade forms.

💡 In one line: Sulfolane is a polar, water-miscible, thermally stable solvent that dissolves things other solvents can't - without evaporating easily or reacting with what it dissolves.

2. Structure & Key Properties 🔬

The molecule's behavior comes directly from its split personality: the polar sulfonyl group (S=O) makes it mix freely with water, while the four-carbon ring gives it affinity for organic compounds. This combination is the secret behind its solvent power.

Here is a quick orientation table. For the full, certified specification, always refer to the product datasheet and SDS.

Characteristic	Typical Value (approx.)
Chemical formula	(CH₂)₄SO₂ · C₄H₈O₂S
CAS number	126-33-0
Appearance	Colorless liquid (solid below ~28 °C)
Polarity	High - dielectric constant ≈ 43, dipole moment ≈ 4.7 D
Thermal stability	Stable to ~220 °C; very high flash point
Water behavior	Fully miscible; hygroscopic

📌 Want exact numbers for boiling point, density, viscosity, and purity? Those live on the product specification page and in our deep-dive on sulfolane solubility & water behavior.

3. Why Sulfolane Is Such a Useful Solvent ✅

Sulfolane earns its place in so many processes because it ticks boxes that few single solvents can:

✅ High polarity - dissolves polar organics, salts, and gases that nonpolar solvents reject.

✅ Aprotic - it has no acidic O–H/N–H protons, so it won't interfere in many reactions or react with sensitive substrates.

✅ Thermally robust - works at elevated temperatures where lighter solvents would boil away or decompose.

✅ Low volatility & high flash point - lower evaporation losses and a safer handling profile than many flammable solvents.

✅ Selective extraction power - pulls aromatics out of mixed hydrocarbon streams with high efficiency.

4. Major Uses & Applications 🏭

Sulfolane's versatility means it shows up across several very different industries. Here are the big ones:

🔹 Aromatic (BTX) Extraction

Its flagship application: selectively extracting benzene, toluene, and xylene from reformer and pyrolysis streams via extractive distillation - the well-known UOP/Shell Sulfolane process. We cover the mechanics in our guide to sulfolane in aromatic extraction & BTX recovery.

🔹 Gas Treating & Sulfur Removal

As the physical-solvent component of the Sulfinol process, sulfolane helps strip H₂S and CO₂ from natural gas, complementing the usual alkanolamine chemistry.

🔹 Electronics & Battery Electrolytes

High-purity, electronic-grade sulfolane is used in semiconductor processing and increasingly as a high-voltage, flame-retardant electrolyte solvent for advanced lithium-ion and sodium-ion batteries. More in our article on sulfolane in electronics & battery electrolytes.

🔹 Chemical & Pharmaceutical Synthesis

As a reaction medium it shines in halogen-exchange (Halex) reactions, sulfonations, and other high-temperature transformations. See our deep-dive on sulfolane as a reaction solvent.

🔹 Other Roles

It also serves as a plasticizer, a curing aid for epoxy resins, a polymerization solvent for high-performance polysulfone resins, and a component in some hydraulic fluids.

5. Sulfolane vs NMP vs DMSO 🆚

Engineers often weigh sulfolane against other dipolar aprotic solvents. At a glance:

Solvent	Stand-out strength	Watch-out
Sulfolane	Thermal stability + selective aromatic extraction	High freezing point (~28 °C); hygroscopic
NMP	Excellent dissolving power for polymers	Reproductive-toxicity regulatory pressure
DMSO	Very high polarity, low cost	Strong skin penetration; lower thermal ceiling

For a full side-by-side on polarity, toxicity, and regulatory status, read Sulfolane vs NMP vs DMSO vs DMF.

6. Grades & Sourcing 📦

Sulfolane is supplied in industrial/technical grade (for extraction and gas treating) and high-purity electronic grade (for batteries and semiconductors). Anhydrous and aqueous (e.g. 80% w/w) forms are also common. Choosing the right grade matters: see sulfolane grades & derivatives and our price & sourcing guide.

As a specialty chemical exporter serving 50+ countries, Sinolook Chemical supplies both grades with full documentation. Explore the electronic-grade Sulfolane product page for specs, packaging, and SDS downloads.

7. Safety at a Glance ⚠️

Sulfolane has a relatively mild acute-toxicity profile and a high flash point, but it is not hazard-free - it carries health-hazard classifications and should be handled with proper PPE and containment. Because it is water-soluble and persistent, environmental release is a genuine concern, as the well-documented North Pole, Alaska groundwater case shows. We cover both topics in depth in sulfolane safety & toxicity and sulfolane in the environment.

⚠️ Always consult the current Safety Data Sheet before handling. Download the SDS from our product page.

🔗 Authoritative references: PubChem (CID 31347) · ECHA Substance Info · NIST WebBook

8. Frequently Asked Questions ❓

🔹 Is sulfolane a polar or nonpolar solvent?

It is strongly polar and aprotic, with a dielectric constant around 43 and a high dipole moment - yet it still mixes well with many organics thanks to its hydrocarbon ring.

🔹 Is sulfolane soluble in water?

Yes - it is fully miscible with water in all proportions and is also hygroscopic, readily picking up moisture from the air.

🔹 What is sulfolane mainly used for?

Its largest use is extracting aromatics (BTX) in refineries. It is also used in gas treating, battery electrolytes, electronics, and chemical/pharmaceutical synthesis.

🔹 What's the difference between sulfolane and tetramethylene sulfone?

They are the same compound - "tetramethylene sulfone" is simply an older systematic name for sulfolane.

🔹 Is sulfolane a green solvent?

It has a favorable low-volatility, high-flash-point profile, but it is not classified as a "green" solvent - its water solubility and environmental persistence require responsible handling. See our environmental article for the full picture.