Iodoform

Overview
The compound iodoform is CHI3. A pale yellow, crystalline, volatile substance, it has a penetrating odor (in older chemistry texts, the smell is sometimes referred to as the smell of hospitals) and, analogous to chloroform, sweetish taste. It is slightly soluble in glycerol, petroleum ether or alcohol (78 g/l at 25 °C), averagely soluble in chloroform, acetic acid and ether (136 g/l at 25 °C) and easily soluble in benzene and acetone (120 g/l at 25 °C).

Physical properties
Its entalphy of sublimation is 69.9 kJ.mol-1 at range of temperatures 35 - 92 °C.

Iodoform molecule parameters are: d(C-I) = 2.12 ± 0.04 Å, d(I-I) = 3.535 ± 0.01 Å and I-C-I = 113°. Dipole moment is 1 D. Its space group is P63 and lattice constants are a = 6.83 Å, c = 7.52 Å.

It has critical point at 584.85 °C, 5.63 MPa. Refractive index is 1.786 (D, 20 °C).

Synthesis
It was first prepared by Georges Serrulas in 1822 and its molecular formula was identified by Jean-Baptiste Dumas in 1834.

Iodoform can be 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, where R is an organic side chain.
 * acetaldehyde: CH3CHO
 * ethanol: CH3CH2OH
 * secondary alcohols: CH3CHROH, where R is an alkyl or aryl group.



These reactions are so reliable that it is called the iodoform test, signalled by the precipitation of pale yellow crystals.

Reactions
Some reagents (e.g. hydroiodic acid) can convert iodoform to diiodomethane.

Also conversion to carbon dioxide is possible. Iodoform reacts with silver nitrate producing carbon monoxide, which is oxidized by mixture of sulfuric acid and iodine pentaoxide.

Uses
It was used in medicine as a healing and antiseptic dressing for wounds and sores around the beginning of the 20th century, though this use is now superseded by better antiseptics.