Difference between revisions of "Thionyl chloride"

Revision as of 20:41, 23 March 2019

Thionyl chloride is an inorganic compound with the chemical formula SOCl₂. It is an extremely useful compound in chemistry, but it is extremely dangerous and toxic.

Thionyl chloride is sometimes confused with sulfuryl chloride, SO₂Cl₂, but the properties of these compounds differ significantly: Thionyl chloride is a source of chloride ions, while sulfuryl chloride is a source of chlorine.

Properties

Chemical

Thionyl chloride reacts on contact with water to form sulfur dioxide and hydrogen chloride/hydrochloric acid mist, process which is extremely exothermic:

SOCl₂ + H₂O → 2 HCl + SO₂

Thionyl chloride will convert carboxylic acids to acyl chlorides:

SOCl₂ + RCO₂H → RC(O)Cl + SO₂ + HCl

This reaction can be used to synthesize acetic anhydride.

Physical

Thionyl chloride is a colorless oily liquid that fumes in air. Old samples have a yellowish color, due to decomposition. Light accelerates its decomposition. Thionyl chloride reacts with water, carboxylic acids, alcohols and all protic solvents. It is however miscible and soluble in most aprotic solvents, such as benzene, carbon tetrachloride, chloroform, diethyl ether, toluene, xylene. Thionyl chloride melts at −104.5 °C and boils at 74.6 °C. It has a density of 1.638 g/cm³ at 20 °C.

Availability

Thionyl chloride is sold by various chemical suppliers, but due to its hazards it's generally not available to the amateur chemist. Its sale is regulated in many places.

Certain batteries contain small amounts of thionyl chloride, but it's impractical to extract it.

Thionyl chloride is listed on schedule 3 of the Chemical Weapons Convention and ordering large amounts may draw attention of the authorities.

Preparation

Unlike its similar compound sulfuryl chloride, thionyl chloride is much more difficult to synthesize.

Industrially it's prepared by reacting sulfur trioxide with sulfur dichloride:

SO₃ + SCl₂ → SOCl₂ + SO₂

Oleum can be used instead of sulfur trioxide, and this is usually preferred, as pure sulfur trioxide is a nightmare to produce, purify, store and use, while oleum is much easier to handle, even though it's not a pleasant experience either. The higher the sulfur trioxide concentration, the better the reaction yield is.

The resulting thionyl chloride is extracted via fractional distillation, best in low light conditions, under dry atmosphere.

SM user Magpie has made a small amount of thionyl chloride.

A more dangerous method involves the reaction between sulfur dioxide and phosgene:

SO₂ + COCl₂ → SOCl₂ + CO₂

However, due to phosgene's extreme toxicity, it's best to avoid this reaction all together.

Projects

• Make acyl chloride
• Make anhydrous metal chlorides
• Make anhydrous alcoholic solutions of HCl

Handling

Safety

Thionyl chloride is extremely toxic and should not be handled unless you're a professional. It reacts violently with water to give sulfur dioxide and hydrochloric acid, which are toxic and corrosive.

Storage

Thionyl chloride is best stored in sealed bottles, in a special cabinet, away from any light and moisture.

Disposal

Thionyl chloride can be safely neutralized by adding it to an alkaline slurry or with dry calcium or sodium carbonate or bicarbonate. Neutralization must be done outside, or in a fumehood, as the neutralization releases a corrosive mist of HCl.

References

Relevant Sciencemadness threads

• Preparation of Thionyl Chloride
• thionyl chloride synthesis
• HELP! need thionyl chloride(SOCl2) synthesis
• thionyl chloride and potassium dichromate