Iodoform (also known as triiodomethane and, inaccurately, as carbon triiodide) is the organoiodine compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

C H I₃. A pale yellow, crystalline, volatile substance, it has 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 Chloroform, or trichloromethane, is an organic compound with formula C H Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to PTFE. It is also a precursor to various ...

, sweetish taste. It is occasionally used as a

disinfectant A disinfectant is a chemical substance or compound used to inactivate or destroy microorganisms on inert surfaces. Disinfection does not necessarily kill all microorganisms, especially resistant bacterial spores; it is less effective than s ...

Structure

The molecule adopts

tetrahedral molecular geometry In a tetrahedral molecular geometry, a central atom is located at the center with four substituents that are located at the corners of a tetrahedron. The bond angles are cos−1(−) = 109.4712206...° ≈ 109.5° when all four substituents a ...

with C_3v

symmetry Symmetry (from grc, συμμετρία "agreement in dimensions, due proportion, arrangement") in everyday language refers to a sense of harmonious and beautiful proportion and balance. In mathematics, "symmetry" has a more precise definiti ...

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 John Thomas Cooper (1790–1854) was an English chemist notable as a lecturer, chemical supplier and chemical analyst, at a time when interest was burgeoning in chemistry as a discipline of study and application. Biography Cooper was born in Gre ...

. 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 In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double b ...

(CH₃COR),

acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the ...

(CH₃CHO),

ethanol Ethanol (abbr. EtOH; also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound. It is an alcohol with the chemical formula . Its formula can be also written as or (an ethyl group linked to a ...

(CH₃CH₂OH), and certain secondary

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s (CH₃CHROH, where R is an alkyl or aryl group). : The reaction of iodine and base with

methyl In organic chemistry, a methyl group is an alkyl derived from methane, containing one carbon atom bonded to three hydrogen atoms, having chemical formula . In formulas, the group is often abbreviated as Me. This hydrocarbon group occurs in ...

s 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

group in alpha-position. Some reagents (e.g.

hydrogen iodide Hydrogen iodide () is a diatomic molecule and hydrogen halide. Aqueous solutions of HI are known as hydroiodic acid or hydriodic acid, a strong acid. Hydrogen iodide and hydroiodic acid are, however, different in that the former is a gas under ...

) convert iodoform to diiodomethane. Also conversion to

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...

is possible: Iodoform reacts with aqueous

silver nitrate Silver nitrate is an inorganic compound with chemical formula . It is a versatile precursor to many other silver compounds, such as those used in photography. It is far less sensitive to light than the halides. It was once called ''lunar causti ...

to produce

carbon monoxide Carbon monoxide ( chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simpl ...

. When treated with powdered elemental silver the iodoform is reduced, producing

acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...

. 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, although this use is now superseded by superior

antiseptic An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...

s. It is the active ingredient in many ear powders for dogs and

cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is commonly referred to as the domestic cat or house cat to distinguish it from the wild members of ...

s, along with

zinc oxide Zinc oxide is an inorganic compound with the formula . It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement ...

and

propionic acid Propionic acid (, from the Greek words πρῶτος : ''prōtos'', meaning "first", and πίων : ''píōn'', meaning "fat"; also known as propanoic acid) is a naturally occurring carboxylic acid with chemical formula CH3CH2CO2H. It is a li ...

, which are used to prevent infection and facilitate removal of ear hair.

References

External links

*
MSDS at JT BakerA Method for the Specific Conversion of Iodoform to Carbon DioxidePreparation
* {{Use dmy dates, date=April 2017 Iodoalkanes Halomethanes Antiseptics Iodine-containing natural products