Iron chloride density is a chemical compound with the formula FeCl3 and an oxidation state of +3. The crystalline compound has a dark green color by reflected light and a purple-red color by transmitted light. It is soluble in methanol and ethanol and reacts with Lewis acids such as triphenylphosphine oxide to form adducts.

It is a mild oxidizing agent and can be used to prepare metal chlorides. It is also a strong Lewis acid and can act as a catalyst in many reactions such as the Friedel–Crafts reaction and chlorination of aromatic compounds. It is an important raw material in the manufacture of vinyl chloride, a commodity chemical.

In the laboratory, iron chloride is an excellent reducing agent for organic molecules and is used as a starting material in a number of organic syntheses. It is also used as an oxidizing agent for the preparation of some metal compounds such as copper(II) chloride and iron(II) chloride.

Chronic exposure to ferric chloride is toxic in animals and induces behavioral convulsions. The toxicity is due to the accumulation of free iron in brain regions. Inhalation of 3.1 mg/cu cm FeCl3 for 2 months in rabbits increased lung alveolar macrophage numbers and caused their accumulation in large granulomas. Macrophage ultrastructure showed marked alterations in their lysosomal inclusions.

In the carotid artery of rats, FeCl3 induced a mixed thrombus composed of activated platelets and fibrin strands with entrapped erythrocytes. The time to occlusion was measured and found to increase dose dependently. The time to occlusion was linked to endothelial injury and vascular damage in the region of the thrombus.