Generation in the laboratory generally follows textbook preparation methods based either on the reduction of hydrochloric acid by oxidizing agents, such as KMnO4 and MnO2, or on the oxidation of hypochlorite. Due to the substantial enthalpy change associated with these reactions, they are rather cumbersome and are dif‘cult to maintain at the constant rate required to produce a steady ¦ow of gas. They also generate a substantial amount of contaminants, such as oxygen, hydrochloric acid, and water vapor. Presented is a simple method based on the co-proportionation of trichloroisocyanuric acid C3N3O3Cl3 (TCCA, a chlorimide) with hydrochloric acid in the following reaction-driven essentially by entropy and, hence, not associated with substantial evolution of heat
The reaction proceeds at room temperature, without heating, so that the amount of water vapor and HCl volatilized with the chlorine is substantially reduced, making desiccation with a single P2O5 stage possible (0.03 mL H2O/1 L Cl2, compared to 2-3 mL H2O/1 L Cl2 for hypochlorite). At the same time, very little oxygen is generated (<0.3% O2 compared to 1.6% for hypochlorite). This is important as oxygen strongly inhibits both thermal  and photolytic  chlorination. The reaction is quantitative, so the addition of a calculated amount of chlorine is easy to implement.