Iodoform
Chemical compound
Iodoform (also known as triiodomethane) is the organoiodine compound with the chemical formula C H I3. It is a pale yellow, crystalline, volatile substance, with a penetrating and distinctive sweetish and chloroform-like odor (in older chemistry texts, the smell is sometimes referred to as that of hospitals, where the compound is still commonly used) and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant.
01Naming and structure
The name iodoform originates with the "formyle radical," an archaic term for the HC moiety, and is retained for historical consistency. A full, modern name is triiodomethane.
The molecule adopts a tetrahedral geometry with C3v symmetry.
02Synthesis and reactions
The synthesis of iodoform was first described by Georges-Simon Serullas in 1822, by reactions of iodine vapour with steam over red-hot coals, and also by reaction of potassium with ethanolic iodine in the presence of water; and at much the same time independently by John Thomas Cooper. It is synthesized in the haloform reaction by the reaction of iodine and sodium hydroxide with any one of these four kinds of organic compounds: a methyl ketone (CH3COR), acetaldehyde (CH3CHO), ethanol (CH3CH2OH), and certain secondary alcohols (CH3CHROH, where R is an alkyl or aryl group).
The reaction of iodine and base with methyl ketones is so reliable that the iodoform test (the appearance of a yellow precipitate) is used to probe the presence of a methyl ketone. This is also the case when testing for specific secondary alcohols containing at least one methyl group in alpha-position.
Some reagents (e.g. hydrogen iodide) convert iodoform to diiodomethane. Conversion to carbon dioxide is also possible. Iodoform reacts with aqueous silver nitrate to produce carbon monoxide. When treated with powdered elemental silver the iodoform is reduced, producing acetylene. Upon heating iodoform decomposes to produce diatomic iodine, hydrogen iodide gas, and carbon.
Natural occurrence
The angel's bonnet mushroom contains iodoform, and shows its characteristic odor.
03Applications
The compound finds small-scale use as a disinfectant. Around the beginning of the 20th century, it was used in medicine as a healing and antiseptic dressing for wounds and sores and, although this use is now largely superseded by safer antiseptics, it is still used in otolaryngology in the form of bismuth subnitrate iodoform paraffin paste (BIPP) as an antiseptic packing for cavities. It is the active ingredient in many ear powders for dogs and cats, along with zinc oxide and boric acid, which are used to prevent infection and facilitate removal of ear hair.
Sources and credits
This article is adapted from the Wikipedia article “Iodoform”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Iodoform in a test tube.jpg by Eugene.negrobov, CC BY-SA 4.0
- Iodoform.jpg by GOKLuLe 盧樂, CC BY-SA 3.0
Fathomly is not affiliated with or endorsed by the Wikimedia Foundation. Spotted a problem? Tell us.
