Magnesium chloride MgCl2 is a salt, and as such, it does not have a specific boiling point like a pure substance. Instead, it will dissociate into its ions Mg2+ and 2Cl- when dissolved in water, and the boiling point of the solution will depend on the concentration of MgCl2 in the water.However, if you are referring to the decomposition temperature of solid magnesium chloride, it starts to decompose at around 714C 1317F into magnesium chloride hexahydrate and hydrochloric acid.