Chromium(II) chloride
Chromium(II) chloride, also known as chromous chloride, is an inorganic compound with the chemical formula CrCl2. It exists as a pale blue solid, and in solution is a strong reducing agent. It is highly air-sensitive, readily oxidizing to chromium(III) species upon exposure to air.
Preparation:
Chromium(II) chloride is typically prepared by reducing chromium(III) chloride (CrCl3) with a reducing agent, such as zinc metal or hydrogen gas at high temperatures. The reaction with zinc is generally carried out in anhydrous conditions to prevent the formation of chromium(III) hydroxide or other unwanted byproducts. Another method involves the reaction of chromium metal with hydrogen chloride gas at elevated temperatures.
Properties:
Chromium(II) chloride is a paramagnetic solid. It dissolves in water to give intensely blue solutions. These solutions are unstable in air, reacting rapidly with oxygen to form chromium(III) species. The reduction potential of Cr3+ to Cr2+ is relatively low, making CrCl2 a useful reducing agent in organic and inorganic chemistry.
Uses:
Chromium(II) chloride finds application as a reagent in various chemical syntheses, particularly in organic chemistry. It is used for the reduction of alkyl halides, aldehydes, and ketones. It also plays a role in certain coupling reactions. Historically, it has seen use in the preparation of other chromium compounds. Due to its strong reducing power and air sensitivity, its use requires careful handling under an inert atmosphere.
Safety:
Chromium(II) chloride is corrosive and an irritant. Exposure to skin and eyes should be avoided. Appropriate personal protective equipment, such as gloves and eye protection, should be worn when handling this compound. It should be stored in a tightly sealed container under an inert atmosphere to prevent oxidation.