Iodoform

Synthesis 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 induces its characteristic odor.

Applications

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it was used in medicine as a healing and antiseptic dressing for wounds and sores and, although this use is now largely superseded by safer antiseptics, it is still used in otolaryngology in the form of bismuth subnitrate iodoform paraffin paste (BIPP) as an antiseptic packing for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.