Simazine is an herbicide of the triazine class. The compound is used to control broad-leaved weeds and annual grasses.

Simazine may be prepared from cyanuric chloride and a concentrated solution of ethyl amine (at least 50 percent by number) in water.^[1] The reaction is highly exothermic and is therefore best carried out below 10 °C.

Cyanuric chloride decomposes at high temperatures into hydrogen chloride and hydrogen cyanide, both of which are highly toxic by inhalation.

Simazine is an off-white crystalline compound which is sparingly soluble in water. It is a member of the triazine-derivative herbicides, and was widely used as a residual non-selective herbicide, but is now banned in European Union states.^[2] Like atrazine, a related triazine herbicide, it acts by inhibiting photosynthesis. It remains active in the soil for two to seven months or longer after application.

• Atrazine

• Simazine, Extoxnet PIP