Phenothiazine, an organic compound with the formula C12H9NS and a molecular weight of 199.272, is a yellow to greenish-gray powder or sheet crystal. Soluble in benzene, ether and acetic acid, slightly soluble in alcohol and mineral oil, almost insoluble in petroleum ether; Chloroform and water. Long storage color becomes dark, easy to oxidize under the sun, can sublimate. It is widely used in the production of acrylic acid, acrylic ester, methacrylate and vinyl acetate as an excellent polymer inhibitor. It is also used in the synthesis of drugs, dyes, polyethers, antioxidants and rubber antiaging agents. It is also used as deworming drug for livestock and insecticide for fruit trees.

Phenothiazine is an organic aromatic compound composed of two benzene rings (phenothiazine parent nucleus) connected by sulfur and nitrogen atoms. Recrystallized from ethanol or benzene is an orthorhombic yellow or gray-green prismatic crystal, and precipitated from toluene or butanol is a yellow leaf crystal, which is volatilized with water vapor. Insoluble in water, petroleum ether and chloroform, slightly soluble in ethanol and mineral oil, soluble in ether and acetone, easily soluble in benzene and hot acetic acid, 25℃ solubility (g/100g) : acetone 25.40, ethanol 3.40, benzene 32.0. Under the sun and in the air, the color becomes darker, and 0.3% methylamine can be added for protection when stored. It also tends to darken when there are impurities. Decomposition in contact with acid and acid vapor, and produce toxic nitrogen oxide and sulfur oxide gas.

Phenothiazine has sublimation, weak isoodor, irritation to the skin, can cause maculae, can also be absorbed through the skin, cause visceral disorders. Rat transoral LD50 5000mg/kg. The maximum allowable concentration in the workplace is 5mg/m3. The laboratory produces this by heating diphenylamine with sulfur at the same time until hydrogen sulfide free gas is released. Phenothiazine is an intermediate in the manufacture of methylene blue dyes. It is also used in the manufacture of an important class of antipsychotic and antihistamines such as chlorpromazine, perphenazine, promethazine and methydiazine.

In addition, phenothiazine can also be used as an inhibitor of ethylene acetate, raw material of rubber antiaging agent, synthetic dye, medicine, pesticide for fruit trees and insect repellent for livestock, etc.