SO₂ reacts with Cl₂ in the presence of sunlight to form.

Sulphur dioxide reacts directly with halogens to forming sulphuryl fluoride, chloride and bromide respectively. Sulphur dioxide combines with chlorine gas in the presence of sunlight to give sulphuryl chloride  SO₂Cl₂.

        SO₂ (g)    +    Cl₂ (g)  +  hν      SO₂Cl₂

Sulphuryl chloride SO₂Cl₂  sometimes confused with thionyl chloride SOCl₂. But they both have different properties. SO₂Cl₂ is used as the source of chlorine Cl₂. While SOCl₂ is the source of chloride ions.

Sulphuryl chloride SO₂Cl₂  is used for the conversion of  C-H bond into C-Cl bond.