Iodoform

The term 'iodoform' was also used in World War II to refer to group keys sent to agents in Europe by the Special Operations Executive: this usage is unrelated to the chemical.

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).

Additional recommended knowledge

Essential Laboratory Skills Guide

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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.

For this reason iodoform was traditionally used as a test for methyl ketone; if a methyl ketone is present in the solution, a yellow precipitate will form. This is known as the iodoform test.

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a healing and antiseptic dressing for wounds and sores around the beginning of the 20th century, though this use is now superseded by better antiseptics.

References

• Merck Index, 12 Edition, 5054.

See also

• Haloalkane
• Halomethane
• Trihalomethane
• Iodomethane
• Diiodomethane
• Carbon tetraiodide (Tetraiodomethane)
• Fluoroform
• Chloroform
• Bromoform

• Iodoform reaction