Sulphuryl chloride - SO2Cl2
Pure sulphuryl chloride is a colorless liquid, but in practice a sample soon turns yellowish green. The compound is made by reacting dry SO2 with dry Cl2 with a suitable catalyst (camphor or active carbon). There is an equilibrium between SO2 + Cl2 and SO2Cl2. This equilibrium is strongly to the side of SO2Cl2, but in real samples there will always be a greenish yellow color, especially when the sample is somewhat older.
The compound SO2Cl2 has a very pungent smell and in contact with water it slowly hydrolyses, giving a mix of sulphuric acid and hydrochloric acid. This reaction with water is not violent, it takes hours to dissolve a blob of a few ml of this compound in a large excess amount of water.