# Are Organic Solvents used in Addition Reactions catalysts?

Say for example you are performing a halogenation reaction with dichloromethane (DCM) as the solvent:

ethylene + chlorine $\stackrel{DCM}\longrightarrow$ 1,2-dichloroethane

I have 2 questions:

1. Is the DCM acting as a catalyst to the reaction, or just a solvent? And if just a solvent, why do we have to use an organic solvent, why not water?
2. Are solvents like DCM necessary if the reactants are liquids already, or only for gaseous or solid reactions?

Thank you

• As for not using water, try dissolving some non-polar organics in water, then you'll see why. Also, water+chlorine would spark a whole bunch of side reactions we don't want to have. – Ivan Neretin Oct 13 '15 at 7:58