Calcium hydroxide reacts with chlorine to form:

Calcium hypochlorite is an inorganic compound with the formula Ca(ClO)₂. Calcium hydroxide and chlorine react together to form bleaching powder. 

$2\mathrm{Ca}{\left(\mathrm{OH}\right)}_2 + 2{\mathrm{Cl}}_2 \to \mathrm{Ca}{\left(\mathrm{OCl}\right)}_2 + {\mathrm{CaCl}}_2 + 2{\mathrm{H}}_2\mathrm{O}$