Iodoform

Iodoform (also known as triiodomethane) is the organoiodine compound with the chemical formula CHI₃. 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.

Iodoform

Names
Preferred IUPAC name Triiodomethane
Other names Iodoform Carbon hydride triiodide Carbon triiodide
Identifiers
CAS Number	75-47-8^Y
3D model (JSmol)	Interactive image
Beilstein Reference	1697010
ChEBI	CHEBI:37758^Y
ChEMBL	ChEMBL1451116^N
ChemSpider	6134^Y
ECHA InfoCard	100.000.795
EC Number	200-874-5
KEGG	D01910^Y
MeSH	iodoform
PubChem CID	6374
RTECS number	PB7000000
UNII	KXI2J76489^Y
CompTox Dashboard (EPA)	DTXSID4020743
InChI InChI=1S/CHI3/c2-1(3)4/h1H^Y Key: OKJPEAGHQZHRQV-UHFFFAOYSA-N^Y
SMILES IC(I)I
Properties
Chemical formula	CHI3
Molar mass	393.732 g·mol^−1
Appearance	Pale, light yellow, opaque crystals
Odor	Saffron-like
Density	4.008 g/cm^3
Melting point	119 °C (246 °F; 392 K)
Boiling point	218 °C (424 °F; 491 K)
Solubility in water	100 mg/L
Solubility in diethyl ether	136 g/L
Solubility in acetone	120 g/L
Solubility in ethanol	78 g/L
log P	3.118
Henry's law constant (kH)	3.4 μmol·Pa^−1·kg^−1
Magnetic susceptibility (χ)	−117.1·10^−6 cm^3/mol
Structure
Crystal structure	Hexagonal
Molecular shape	Tetrahedral at C
Thermochemistry
Heat capacity (C)	157.5 J/(K·mol)
Std enthalpy of formation (ΔfH^⦵298)	180.1 – 182.1 kJ/mol
Std enthalpy of combustion (ΔcH^⦵298)	−716.9 – −718.1 kJ/mol
Pharmacology
ATC code	D09AA13 (WHO)
Hazards
GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H315, H319, H335
Precautionary statements	P261, P280, P305+P351+P338
NFPA 704 (fire diamond)	2 1 1
Flash point	204 °C (399 °F; 477 K)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	355 mg/kg (oral, rat) 1180 mg/kg (dermal, rat) 1.6 mmol/kg(s.c., mouse)
NIOSH (US health exposure limits):
PEL (Permissible)	none
REL (Recommended)	0.6 ppm (10 mg/m^3)
IDLH (Immediate danger)	N.D.
Related compounds
Related compounds	Methyl iodide Diiodomethane Carbon tetraiodide Fluoroform Chloroform Bromoform
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references

Naming

The name iodoform originates with the "formyle radical," an archaic term for the HC moiety,^{[citation needed]} 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, though the IUPAC recommends against doing so, as "carbon triiodide" could also mean C₂I₆ (hexaiodoethane, a highly unstable compound).

Structure

The molecule adopts a tetrahedral geometry with C_3v 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; 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 shows 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 superior 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 propionic acid, which are used to prevent infection and facilitate removal of ear hair.^{[citation needed]}

See also

• Fluoroform
• Chloroform
• Bromoform