iodoform

 

(īō'dəfôrm') , CHI₃, yellow crystalline solid that has a penetrating odor. It melts at 119°C and is insoluble in water but soluble in ether or ethanol. Iodoform was formerly used as an antiseptic. It is produced when a methyl ketone, acetaldehyde, or an alcohol with the formula RCHOHCH₃ (where R is hydrogen or an alkyl or aryl group) is treated with sodium hydroxide and iodine.

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.

Iodoform
IUPAC name	Iodoform
Other names	Triiodomethane, Methyl triiodide, Carbon triiodide, TIM
Identifiers
CAS number	75-47-8
PubChem	6374
EINECS number	200-874-5
KEGG	D01910
ChEBI	37758
RTECS number	PB7000000
SMILES	C(I)(I)I
InChI	InChI=1/CHI3/c2-1(3)4/h1H
Properties
Molecular formula	CHI3
Molar mass	393.73 g/mol
Appearance	Yellowish crystalls
Density	4.008 g/cm3
Melting point	123 °C
Boiling point	217 °C (expl.)
Solubility in water	0.1 g/l at 20 °C
log P	3.83
kH	0.34 mol.kg-1.bar-1
Structure
Crystal structure	Hexagonal
Molecular shape	Tetrahedral
Hazards
EU classification	Harmful (Xn), Dangerous for the environment (N)
NFPA 704	0 2 1
R-phrases	R20/21/22, R36/37/38
S-phrases	S22, S26, S36/37/39
Flash point	204 °C
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

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.

References

• Merck Index, 12 Edition, 5054.

See also

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

• Iodoform reaction

External links

• NIOSH Pocket Guide to Chemical Hazards 0343
• MSDS at Oxford University
• MSDS at Science Lab
• A Method for the Specific Conversion of Iodoform to Carbon Dioxide
• Article at 1911 Encyclopaedia Britannica
• Preparation

Medicated dressings (D09)
Framycetin - Fusidic acid - Nitrofural - Phenylmercuric nitrate - Benzododecinium - Triclosan - Cetylpyridinium - Aluminium chlorohydrate - Povidone-iodine - Clioquinol - Benzalkonium - Chlorhexidine - Iodoform

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