What Is Iodobenzene?
Iodobenzene is an organic compound with the chemical formula C6H5I, classified as an organic halide.
This compound is synthesized by the reaction of benzene with iodine or sulfur iodide and nitric acid under heating conditions.
It is recognized as a flammable liquid, acutely toxic (oral), and an eye irritant under the Globally Harmonized System (GHS). Additionally, iodobenzene falls under hazardous and toxic substances in the Industrial Safety and Health Law and is designated as Hazardous Substance Class 4 and Petroleum No. 3 in the Fire Service Law. It is commercially available for various applications.
Uses of Iodobenzene
Iodobenzene serves as a crucial synthetic intermediate in organic chemistry, particularly useful in reactions involving the phenyl group—a structure prevalent in many natural and synthetic compounds.
It is employed as a substrate in palladium-catalyzed cross-coupling reactions and in the formation of Grignard reagents through its reaction with magnesium.
Properties of Iodobenzene
With a melting point of -29°C and a boiling point of 188°C, iodobenzene appears as a clear, colorless to reddish-brown liquid, possessing a volatile, distinct odor and becomes reddish over time. It is soluble in organic solvents but insoluble in water.
Upon exposure, iodine is released, and iodobenzene can react with metallic sodium to synthesize biphenyl or with sodium hydroxide to form phenol. Its carbon-iodine bond is weaker than those in chlorobenzene and bromobenzene, making it highly reactive for introducing phenyl groups into target molecules.
Structure of Iodobenzene
Iodobenzene features a benzene ring where one hydrogen atom is substituted with an iodine atom. It has a molar mass of 204.01 g/mol and a density of 1.831 g/cm3.
Other Information on Iodobenzene
1. Synthesis of Iodobenzene
Apart from the primary method, iodobenzene can also be synthesized through the Sandmeyer reaction, which involves diazotizing aniline and then adding potassium iodide with copper salts as catalysts. This process starts with the formation of diazonium salts from aromatic amines and sodium nitrite in a hydrochloric acid solution under cold conditions. The subsequent exchange with potassium iodide and temperature increase leads to nitrogen gas release and iodobenzene formation. Purification involves base neutralization of excess nitrite, followed by acidification and steam distillation of the iodobenzene.
2. Iodobenzene as a Synthetic Intermediate
Reacting iodobenzene with magnesium produces phenylmagnesium iodide, a Grignard reagent acting as a synthetic phenyl anion. This makes phenylmagnesium iodide interchangeable with phenylmagnesium bromide in synthetic applications.
3. Coupling Reaction of Iodobenzene
Iodobenzene is a preferred substrate for palladium-catalyzed cross-coupling reactions, including the Sonogashira coupling and the Heck reaction. The Sonogashira coupling, which synthesizes alkynylated aryl compounds from an aryl halide and a terminal alkyne, utilizes a palladium catalyst, a copper catalyst, and a base. The Heck reaction, also known as the Mizoroki-Heck reaction, involves the substitution of an alkene’s hydrogen atom with an aryl or alkenyl halide in the presence of a palladium catalyst and a base.