What is the main component of the reagent thionyl chloride?

Thionyl chloride is primarily composed of sulfur and chlorine, with the chemical formula SOCl₂. The name itself indicates that sulfur is a key component. In this reagent, sulfur takes a central role in its reactivity, particularly in the context of converting alcohols to alkyl chlorides and in various other reactions where it acts as a source of chloride ions. Chlorine is also present and plays an important role, but the presence of sulfur is what characterizes thionyl chloride specifically, distinguishing it from other chlorinating agents.

Oxygen is present in thionyl chloride in the form of a double bond to sulfur, but it is not the main component by mass or substance in comparison to sulfur and chlorine. Similarly, carbon is not a component of thionyl chloride at all.