Methyl Iodide

Methyl iodide is also called Iodo methane having Molecular formula CH₃I, Mol. Wt. 141.94 g/mol. It is an important halo alkane derivative of Methane, in which one atom of hydrogen in Methane is replaced by one atom of Iodine. It is an Organo iodine Compound that contains one Carbon – Iodine bond. Methyl iodide contains Methyl group, with formula CH₃ (also called Me). In Methyl Iodide it exists as Methylium cation ( CH₃+) which is obtained by protonation of Methanol. Methyl iodide is highly reactive, the Methylium cation acts as a strong electrophillic Methylating agent, while the Iodide ion is a powerful nucleophile and is a good leaving group . Methyl iodide is a dense, colorless, volatile liquid turns brown on exposure to light due to liberation of Iodine. It has a very low boiling point (B.P. 41-43 °c), Sp. Gr. at 20 °c: 2.27 – 2.28gm/cc. It is slightly soluble in water, miscible with Alcohol, Ether. Being an organo iodide compound, it is sensitive to light and therefore needs to be stored in dark amber colored bottles to prevent its degradation by light. It is stabilized by Copper or Silver wire.
Methyl iodide is prepared by any one of the following methods :
(i) By the reaction of Iodine on Mixture of Methanol and Red phosphorous.
(ii) By the reaction of Dimethyl Sulphate with Potassium Iodide
(iii) By the reaction of Methanol with Potassium iodide catalyzed by Acid.
It finds its main applications :
(i) In the Organic synthesis as a Methylating agent for Methylation of Carboxylic acids ,Phenols.
(ii) It is used in the preparation of Tetra Methyl Ammonium Hydroxide
(iii)It is used in the preparation of Methyl Magnessium Iodide (Grignard reagent).
(Iv) as a pesticide(v) For Preplant soil treatment in the fields of strawberries , peppers, tomatoes.