Iodoform
Stereo, skeletal formula of iodoform with the explicit hydrogen added
Ball and stick model of iodoform
Ball and stick model of iodoform
Freshly made iodoform from an iodine tincture.
Names
Preferred IUPAC name
Triiodomethane
Other names
  • Iodoform[1]
  • Carbon hydride triiodide
  • Carbon triiodide[2]
Identifiers
3D model (JSmol)
1697010
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.795 Edit this at Wikidata
EC Number
  • 200-874-5
KEGG
MeSH iodoform
RTECS number
  • PB7000000
UNII
  • InChI=1S/CHI3/c2-1(3)4/h1H checkY
    Key: OKJPEAGHQZHRQV-UHFFFAOYSA-N checkY
  • IC(I)I
Properties
CHI3
Molar mass 393.732 g·mol−1
Appearance Pale, light yellow, opaque crystals
Odor Saffron-like[3]
Density 4.008 g/cm3[3]
Melting point 119 °C (246 °F; 392 K)[3]
Boiling point 218 °C (424 °F; 491 K)[3]
100 mg/L[3]
Solubility in diethyl ether 136 g/L
Solubility in acetone 120 g/L
Solubility in ethanol 78 g/L
log P 3.118
3.4 μmol·Pa−1·kg−1
−117.1·10−6 cm3/mol
Structure
Hexagonal
Tetrahedral at C
Thermochemistry
157.5 J/(K·mol)
180.1 – 182.1 kJ/mol
−716.9 – −718.1 kJ/mol
Pharmacology
D09AA13 (WHO)
Hazards
GHS labelling:
GHS07: Exclamation mark
Warning
H315, H319, H335
P261, P280, P305+P351+P338
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
2
1
1
Flash point 204 °C (399 °F; 477 K)
Lethal dose or concentration (LD, LC):
  • 355 mg/kg (oral, rat)[3]
  • 1180 mg/kg (dermal, rat)[3]
  • 1.6 mmol/kg(s.c., mouse)[5]
NIOSH (US health exposure limits):
PEL (Permissible)
none[4]
REL (Recommended)
0.6 ppm (10 mg/m3)[4]
IDLH (Immediate danger)
N.D.[4]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Iodoform stored in an ampoule

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.

Naming

The name iodoform originates with the "formyle radical," an archaic term for the HC moiety, and is retained for historical consistency. A full, modern name is triiodomethane. The "hydride" in the latter is sometimes omitted,[2] but 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 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;[6] and at much the same time independently by John Thomas Cooper.[7] 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. Also conversion to carbon dioxide is 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.[5][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. 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

References

Randhawa GK, Graham R, Matharu KS, Bismuth Iodoform Paraffin Paste: History and uses. British Journal of Oral and Maxillofacial Surgery. 2019;67:E53-E54.

  1. ^ "Front Matter". Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. p. 661. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4. The retained names 'bromoform' for HCBr3, 'chloroform' for HCCl3, and 'iodoform' for HCI3 are acceptable in general nomenclature. Preferred IUPAC names are substitutive names.
  2. ^ a b "Iodoform".
  3. ^ a b c d e f g Record in the GESTIS Substance Database of the Institute for Occupational Safety and Health
  4. ^ a b c NIOSH Pocket Guide to Chemical Hazards. "#0343". National Institute for Occupational Safety and Health (NIOSH).
  5. ^ a b Merck Index, 12 Edition, 5054
  6. ^ Surellas, Georges-Simon (1822), Notes sur l'Hydriodate de potasse et l'Acide hydriodique. -- Hydriodure de carbone; moyen d'obtenir, à l'instant, ce composé triple [Notes on the hydroiodide of potassium and on hydroiodic acid -- hydroiodide of carbon; means of obtaining instantly this compound of three elements] (in French), Metz, France: Antoine, pp. 17–20, 28–29
  7. ^ James, Frank A. J. L. (2004). "Cooper, John Thomas". Oxford Dictionary of National Biography (online ed.). Oxford University Press. doi:10.1093/ref:odnb/39361. Retrieved 26 January 2012. (Subscription or UK public library membership required.)
  8. ^ Lyday, Phyllis A. (2005), "Iodine and Iodine Compounds", Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, pp. 1–13, doi:10.1002/14356007.a14_381.pub2, ISBN 9783527306732