Sulfuryl chloride

Sulfuryl chloride

Sulfuryl chloride is an inorganic compound with the formula SO₂Cl₂. At room temperature, it is a colorless liquid with a pungent odor. Sulfuryl chloride is not found in nature, as can be inferred from its rapid hydrolysis.

Sulfuryl chloride is commonly confused with thionyl chloride, SOCl₂. The properties of these two sulfur oxychlorides are quite different: sulfuryl chloride is a source of chlorine whereas thionyl chloride is a source of chloride ions. An alternative IUPAC name is sulfuroyl dichloride.

Sulfur is tetrahedral in SO₂Cl₂, being bound to two oxygen atoms via double bonds and to two chlorine atoms via single bonds. The oxidation state of the sulfur atom is +6, as in H₂SO₄.

Synthesis

SO₂ + Cl₂ à SO₂Cl₂

SO₂Cl₂ is prepared by the reaction of sulfur dioxide and chlorine in the presence of a catalyst, such as activated carbon.  The crude product can be purified by fractional distillation. It is uncommon to prepare SO₂Cl₂ in the laboratory because it is commercially available. Sulfuryl chloride can also be considered a derivative of sulfuric acid.

Reactions

Sulfuryl chloride reacts with water, releasing hydrogen chloride gas and sulfuric acid:

2 H₂O + SO₂Cl₂ à 2 HCl + H₂SO₄

SO₂Cl₂ will also decompose when heated to or above 100 °C, about 30 °C above its boiling point.  Upon standing, SO₂Cl₂ decomposes to sulfur dioxide and chlorine, which gives the older samples a slightly yellowish color.

Uses

Sulfuryl Chloride is the Sulfuric oxychloride where as sulfinyl chloride is the sulfurous oxychloride. Sulfuryl Chloride is a colorless to yellowish liquid with a pungent odor. It boils at 69°C, decomposed by hot water and alkalies; soluble in most organic solvents (benzene, chloroform, carbon tetrachloride and acetic acid). It is not found in nature due to strong hydrolysis. It is explosive also with donor solvents such as alcohols, ethers, DMSO and DMF. It decompose at its boiling point. It has two S-Cl single bonds and two S=O solid bonds. It is prepared by the reaction of sulfur dioxide and chlorine in the presence of activated carbon. It is used as a solvent and as a source of chlorine in chemical reactions. Sulfuryl chloride is useful mainly in preparing pesticides. It is used as a chlorinating (and sulfochlorinating) agent of alcohols, alkyls, aromatics, and epoxides for the target molecules of pharmaceuticals, disinfectants, dyestuffs, rayon, and poison gases. Chlorination in organic synthesis with sulfuryl chloride is more selective than elementary chlorine. It is useful to avoid secondary reactions. Chlorination of alcohols to yield alkyl chloride.

Sulfuryl chloride is often used as a source of Cl₂. Because it is a pourable liquid, it is considered more convenient than Cl₂ to measure, store, and dispense. SO₂Cl₂ is widely used as a reagent in the conversion of C-H → C-Cl adjacent to activating substituents such as carbonyls and sulfoxides. It also chlorinates alkanes, alkenes, alkynes, aromatics, and epoxides. Such reactions occur under free radical conditions using an initiator such as AIBN.

Overall reaction

C₄H₉Cl + SO₂Cl₂+AIBNàC₄H₈Cl₂ + SO₂ + HCl

Below side reaction possible if there is more amount of sulfuryl chloride.

It can also be used to convert disulfides into their corresponding sulfenyl chlorides. SO₂Cl₂ can also convert alcohols to alkyl chlorides. In industry, sulfuryl chloride is most used in producing pesticides.

SO₂Cl₂ can also be used to treat wool to prevent shrinking.

Precautions

SO₂Cl₂ is toxic, corrosive, and acts as a lachrymator. As described above, it can form explosive mixtures with water, as well as donor solvents such as DMSO and DMF.