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The triiodomethane (iodoform) reaction is used to detect the presence of a CH3CO group in aldehydes and ketones . This reaction can be carried out with two reagent mixes that appear to be fairly different. Chemically, they are interchangeable.
Using a solution of iodine and sodium hydroxide
Chemically, this is the more obvious technique. A small amount of aldehyde or ketone is added to an iodine solution, which is then removed with just enough sodium hydroxide solution to eliminate the iodine’s colour. If nothing happens in the cold, the combination may need to be gently warmed. The development of a very pale yellow precipitate of triiodomethane (formerly known as iodoform) – CHI3 – indicates a favourable result. Aside from its colour, this is distinguished by a vaguely “medical” odour. It’s an antibacterial that’s found in sticky plasters used to treat minor cuts, for example.
Using Solution of potassium iodide and sodium chlorate(I)
Sodium hypochlorite is another name for sodium chlorate(I). A little amount of aldehyde or ketone is mixed with potassium iodide solution, then sodium chlorate(I) solution. If no precipitate forms when the mixture is cold, it may be required to carefully warm the mixture. The favourable outcome is the same pale yellow precipitate that was previously observed.
The triiodomethane (iodoform) reaction
An aldehyde or ketone bearing the grouping: gives a positive result – the pale yellow precipitate of triiodomethane (iodoform).
A hydrogen atom or a hydrocarbon group can be used as “R.” (for example, an alkyl group). If “R” is hydrogen, the aldehyde ethanal, CH3CHO, is formed.
The triiodomethane (iodoform) reaction can only be produced by ethanal.
You have a ketone if “R” is a hydrocarbon group. This reaction is triggered by a methyl group on one side of the carbon-oxygen double bond, which is present in many ketones. They are known as methyl ketones.
Equation For Iodoform Reaction
The triiodomethane (iodoform) reaction equations
We’ll use iodine and sodium hydroxide solution as our reagents. The first stage includes iodine atoms replacing all three hydrogens in the methyl group. The presence of hydroxide ions is necessary for the reaction to take place because they are involved in the process.
The connection between the CI3 and the rest of the molecule is broken in the second stage, yielding triiodomethane (iodoform) and an acid salt.
When you add it all up, you obtain the following response equation:
What Does the Iodoform Reaction Indicate?
The development of a pale yellow precipitate of triiodomethane (iodoform) – a positive result – is provided by an alcohol containing the grouping:
A hydrogen atom or a hydrocarbon group can be used as “R.” (for example, an alkyl group). If “R” is hydrogen, you get CH3CH2OH, which is the primary alcohol.
The triiodomethane (iodoform) reaction occurs only with ethanol as the primary alcohol.
We may have a secondary alcohol if “R” is a hydrocarbon group. This reaction occurs in a variety of secondary alcohols, but those that do all have a methyl group attached to the carbon with the -OH group.
Because no tertiary alcohols can have a hydrogen atom attached to the carbon with the -OH group, no tertiary alcohols can contain this group. The triiodomethane (iodoform) reaction does not occur with any tertiary alcohols.
Iodoform’s physical properties
The iodoform has the following significant physical characteristics:
1. It has a melting point of 121 degrees celsius and is a yellow crystalline solid.
2. It has an odour that is distinct and nasty.
3. It is water insoluble, although soluble in ethyl alcohol and ether .
Iodoform’s Chemical Properties
The chemical behaviour of iodoform is almost identical to that of chloroform. Chloroform, on the other hand, is less stable. The following are some of Iodoform’s most important chemical properties:
Raction Of carbylamine Reaction : When Iodoform is burned with a primary (1) amine (aromatic or aliphatic) and alcoholic caustic potash, a comparable isocyanide or carbylamine is produced.
Reduction: When reduced with red phosphorus and hydroiodic acid, it produces methylene iodide.
Hydrolysis : When heated with alcoholic potassium hydroxide, it undergoes a hydrolysis reaction, releasing formic acid, which interacts with KOH to produce potassium formate.
Dehalogenation : When heated with silver powder, it undergoes a dehalogenation reaction and yields acetylene.
Reaction with silver nitrate : Iodoform produces a yellow-colored silver iodide precipitate when heated with alcoholic silver nitrate. In this reaction, it behaves differently from chloroform, which does not precipitate with silver nitrate.
Stability : When heated, iodoform decomposes into iodine vapour. When it comes into touch with air, moisture, or light, it decomposes. Due to the liberation of free iodine, it has an antimicrobial effect.
Conclusion
Iodoform is a highly flammable crystalline pale yellow substance. It is water insoluble, although ethyl alcohol and ether are. The chemical behaviour of iodoform is almost identical to that of chloroform. The presence of an aldehyde or ketone in which a methyl group is one of the groups immediately connected to the carbonyl carbon is detected by the iodoform test. It’s also employed as an antiseptic and in pharmaceutical manufacturing, among other things. Iodoform tests can also be used to distinguish between multiple pairs of chemicals.
