Introduction
Iodobenzene is one Iodine substitution of benzene and its molecular formula is C6H5I. It Is a colorless liquid with special odor, insoluble in water, soluble in trichloromethane, ether and ethanol. It is Photosensitive and gradually turns yellow in case of light. Because the bond energy of C-I is lower than that of C-Cl and C-Br, its reactivity is much stronger. It can react with magnesium to generate grignard reagent Phenylmagnesium Iodide (PhMgI), which can be used as equivalent of phenyl anion in organic synthesis. Iodobenzene can be used as the raw material in Sonogashira coupling reaction, Heck reaction and Other metals catalyzed coupling reaction.
Chemical Properties
Colorless liquid, melting point-31.27℃, boiling point 188.3℃, 63-64℃（1.07kPa）, Flash point 74 ℃,density 1.8308（20/4℃）, refractive index1.6200（18.5℃）
Usage
A general reagent for organic synthesis and used as a standard liquid refractive index
Preparation
Iodobenzene is obtained through the diazotization and replacement reaction of Aniline.
Hydrochloric acid( 30%) and aniline were added to Water, stirred and cooled to 2 ℃. Then, sodium nitrite solution was added dropwise to the above solution and the temperature was controlled to be no more than 12℃. When the last part of sodium nitrite solution was added, potassium iodide starch paper was used to determine the blue reaction endpoint.
Then, diazotization liquid was obtained. Potassium iodide solution was added to the diazotization solution in several batches until no nitrogen was released. After cooling, the upper aqueous solution was separated from the above system. Sodium hydroxide solution (10%) was added until the pH value was 14. A distillation process was carried out and aqueous layer was separated from the distillate. The atmospheric fractionation process was arried out after drying and the fraction at184-188 ℃ was collected, which is iodobenzene with a yield of 77%.
Chemical Properties
CLEAR YELLOW LIQUID
Uses
Iodobenzene is used to prepare biphenyl and stilbene. It reacts with magnesium to form the Grignard reagent, a phenylmagnesium iodide used in organic synthesis. It finds application as a solid chlorine source by reacting with chlorine to form a complex, iodobenzene dichloride. It serves as a substrate in Sonogashira reaction which is used to form a carbon-carbon bond between a terminal alkyne and an aryl halide.
Purification Methods
Wash it with dilute aqueous Na2S2O3, then water. Dry it with CaCl2 or CaSO4, decolourise with charcoal and distil it under reduced pressure then store it with mercury or silver powder to stabilise it. [Beilstein 5 IV 688.]
