Iodoform

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Iodoform
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Template:Longitem 1697010
ChEBI Template:Unbulleted list
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MeSH iodoform
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Template:Longitem Template:Chembox Elements/molecular formula
Molar mass Template:Chem molar mass
Appearance Pale, light yellow, opaque crystals
Odor Saffron-like[1]
Density 4.008 g/cm3[1]
Melting point Template:Chembox CalcTemperatures
Boiling point Template:Chembox CalcTemperatures
Solubility in diethyl ether 136 g/L
Solubility in acetone 120 g/L
Solubility in ethanol 78 g/L
log P 3.118
Template:Longitem 3.4 μmol·Pa−1·kg−1
Template:Longitem −117.1·10−6 cm3/mol
Template:Longitem Hexagonal
Template:Longitem Tetrahedral at C
Template:Longitem 157.5 J/(K·mol)
Template:Longitem 180.1 – 182.1 kJ/mol
Template:Longitem −716.9 – −718.1 kJ/mol
Template:Longitem D09AA13 (WHO)
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File:Iodoform.jpg
Iodoform stored in an ampoule

Iodoform (also known as triiodomethane) is the organoiodine compound with the chemical formula Template:Chem2. It is a pale yellow, crystalline, volatile substance, with a penetrating and distinctive 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.

Naming

The name iodoform originates with the "formyle radical," an archaic term for the HC moiety,Script error: No such module "Unsubst". and is retained for historical consistency. A full, modern name is triiodomethane. Another possible name is "carbon hydride triiodide". The "hydride" in the latter is sometimes omitted,[3] though the IUPAC recommends against doing so, as "carbon triiodide" could also mean Template:Chem2 (hexaiodoethane, a highly unstable compound).

Structure

The molecule adopts a tetrahedral geometry with C3v symmetry.

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;[4] and at much the same time independently by John Thomas Cooper.[5] 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 (Template:Chem2), acetaldehyde (Template:Chem2), ethanol (Template:Chem2), and certain secondary alcohols (Template:Chem2, where R is an alkyl or aryl group).

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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.[6] 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.

Applications

The compound finds small-scale use as a disinfectant.[7][8] 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 superior antiseptics, it is still used in otolaryngology in the form of bismuth subnitrate iodoform paraffin paste (BIPP) as an antiseptic packing for cavities.[9] It is the active ingredient in many ear powders for dogs and cats, along with zinc oxide and propionic acid, which are used to prevent infection and facilitate removal of ear hair.Script error: No such module "Unsubst".

See also

References

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  1. ↑ a b c Record in the GESTIS Substance Database of the Institute for Occupational Safety and HealthScript error: No such module "TemplatePar". Script error: No such module "TemplatePar".
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  4. ↑ Script error: No such module "citation/CS1".
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  8. ↑ Script error: No such module "citation/CS1".
  9. ↑ Script error: No such module "Citation/CS1".

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External links

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