Iodoform was invented in 1822. Electrolysis of aqueous solutions containing acetone, inorganic iodides, and sodium carbonate is used to make it. Iodoform is a pale yellow, crystalline, volatile substance. It has long been used in general medicine as external disinfection and wound dressing. However, it is no longer employed for specific reasons.

Iodoform is an antiseptic component used in medications to treat minor skin diseases; its antiseptic properties were discovered in 1880. Let’s get detailed information on Iodoform, its definition, iodoform tests, uses, etc. Scroll down to learn more!

What is Iodoform?

Iodoform is an organic iodine chemical with the formula \({\text{CH}}{{\text{l}}_3}\) and is a member of the organic halogen family. It is a crystalline pale-yellow material that is highly flammable. Iodoform is also known as triiodomethane. In addition, it is commonly known as the triiodo derivative of methane.

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Structure of Iodoform

Iodoform has a tetrahedral molecular geometry. The iodoform molecule contains \(4\) bonds, of which \(3\) are \({\text{C}} – {\text{I}}\) bonds, and one is a \({\text{C}} – {\text{H}}\) bond.

Preparation of Iodoform

Iodoform is prepared by heating ethanol or propanone with alkali and iodine. This reaction is known as the haloform (Iodoform) reaction.

a) From Ethanol

Iodoform is produced by heating ethanol with iodine in the presence of alkali (\({\text{NaOH}}\) or \({\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}\)) at about \(60\) degrees Celsius. When \({\text{NaOH}}\) is used as an alkali, the reaction proceeds as follows.

I. \({\text{NaOH}}\) reacts with iodine to form sodium hypoiodite.
\(2{\text{NaOH}} + {{\text{I}}_2} \to \underset{{{\text{ Sod}}{\text{. hypoiodite }}}}{\mathop {{\text{NaOI}}}} + {\text{NaI}} + {{\text{H}}_2}{\text{O}}\)

II. Sodium hypoiodite oxidises ethanol to ethanal.
\(\mathop {{\rm{C}}{{\rm{H}}_3}{\rm{C}}{{\rm{H}}_2}{\rm{OH}} + {\rm{NaOI}}}\limits_{{\rm{ Ethanol }}}  \to \mathop {{\rm{C}}{{\rm{H}}_3}{\rm{CHO}}}\limits_{\begin{array}{*{20}{c}}{{\rm{ Ethanal }}}\\{{\rm{ (actaldelyede) }}}\end{array}}  + {\rm{NaI}} + {{\rm{H}}_2}{\rm{O}}\)

III. Ethanal undergoes iodination to form \(2,2,2\)-triiodoethanal.
\(\mathop {\mathop {{\rm{C}}{{\rm{H}}_3}{\rm{CHO}}}\limits_{{\rm{Ethanal}}} }\limits_{\left( {{\rm{acetakdehyde}}} \right)} {\rm{ + }}\,{\rm{3NaOI}}\, \to \,\mathop {\mathop {{{\rm{I}}_3}{\rm{CCHO}}}\limits_{2,2,2\,{\rm{triiodoethanal}}} }\limits_{\left( {{\rm{triodo}}{\mkern 1mu} {\rm{acetaldehyde}}} \right)}  + 3{\rm{NaOH}}\)

IV. Triiodoethanal undergoes hydrolysis to give Iodoform.
\({{\text{I}}_3}{\text{CCHO}} + {\text{NaOH}} \to \underset{{{\text{ Iodoform }}}}{\mathop {{\text{CH}}{{\text{I}}_3}}} + \underset{{{\text{ Sod}}{\text{.fomate }}}}{\mathop {{\text{HCOONa}}}} \)

b) From Propanone (Acetone)

Propanone can also be heated with iodine in the presence of an alkali (\({\text{NaOH}}\) or \({\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}\)) to make Iodoform. The reaction is carried out in the following steps when sodium hydroxide is used.

I. \({\text{NaOH}}\) reacts with iodine to form sodium hypoiodite.
\(2{\text{NaOH}} + {{\text{I}}_2} \to \underset{{{\text{ Sod}}{\text{. hyppoiodite }}}}{\mathop {{\text{NaOI}}}} + {\text{NaI}} + {{\text{H}}_2}{\text{O}}\)

II. Acetone undergoes iodisation to form triiodoacetione.

III.Triiodoacetone undergoes hydrolysis to yield Iodoform.

Physical Properties of Iodoform

The following are the important physical features of the Iodoform:

1. It is a yellow crystalline solid with a melting point of \(121\) degrees Celsius.
2. It has a distinct and unpleasant odour.
3. It is insoluble in water but soluble in ethyl alcohol and ether.

Chemical Properties of Iodoform

Iodoform has a chemical behaviour that is nearly identical to that of chloroform. The only difference is, chloroform is less stable. The significant chemical properties of Iodoform are listed below:

1. Carbylamine reaction: A similar isocyanide or carbylamine is generated when Iodoform is heated with a primary \(\left({{1^ \circ }} \right)\) amine (aromatic or aliphatic) and alcoholic caustic potash. For example,

2. Reduction: It produces methylene iodide when reduced with red phosphorus and hydroiodic acid.

3. Hydrolysis: It undergoes hydrolysis reaction when heated with alcoholic potassium hydroxide, yielding formic acid, which reacts with \({\text{KOH}}\) to generate potassium formate.

4. Dehalogenation: It undergoes a dehalogenation reaction and yields acetylene when heated with silver powder.

5. Reaction with silver nitrate: When Iodoform is heated with alcoholic silver nitrate, it produces a yellow-coloured silver iodide precipitate. It behaves differently in this reaction than chloroform, which does not form a precipitate with silver nitrate.

6. Stability: Iodoform decomposes into iodine vapour when heated. It decomposes when it comes into contact with air, moisture, or light. It has an antibacterial effect due to the liberation of iodine.

Iodoform Reaction (Haloform Reaction)

The haloform reaction occurs when a methyl ketone reacts with iodine in the presence of hydroxide ions, producing a carboxylate ion and a haloform. Acetaldehyde is the only aldehyde that undergoes the haloform reaction.

For example,

Iodoform Test

The iodine test is an important test used to detect the presence of acyl group in a compound. The test is given by all those compounds in which a methyl group is directly attached to a carbonyl group (acyl) or by the compounds which can produce an acyl group upon oxidation, i.e., by the compounds containing group.

Iodoform test is given by following compounds:

1. Ethanol
2. Propan\( – 2 – {\text{ol}}\)
3. Lactic acid
4. Acetaldehyde
5. Methyl ketones

Iodoform Test Mechanism

First, acidic alpha hydrogen is removed by the Hydroxide ion. An enolate ion is formed as a result of this reaction. After that, the enolate anion displaces an iodide ion from the iodine molecule. \({\text{R}} – {\text{CO}} – {\text{C}}{{\text{l}}_3}\) is obtained by repeating this method thrice. A hydroxide ion is now bonded to the carbonyl carbon. The carbonyl group is reformed, and the \({\text{C}}{{\text{I}}_3}^ – \) anion is eliminated as a result. There is also the formation of an \({\text{R}} – {\text{COOH}}\) group. The basic \({\text{C}}{{\text{I}}_3}^ – \) ion and the carboxylic acid group neutralise each other out. The reaction mechanism is as follows:

Iodoform Test for Alcohols

When a chemical compound having a \({\text{C}}{{\text{H}}_3}{\text{CO}} – \) or \({\text{C}}{{\text{H}}_3}{\text{CHOH}} – \) group is heated with iodine and an aqueous solution of sodium carbonate (or sodium hydroxide), a yellow-coloured iodoform precipitate forms. The process involves oxidation, iodination, and hydrolysis (cleavage of the \({\text{C}} – {\text{C}}\) bond) and has already been thoroughly described (see, preparation of Iodoform from ethanol and propanone). The complete reactions for ethanol, propan-\(2\)-one and propan\( – 2 – {\text{ol}}\) are as follows:

1.

or

2.

or

3.

However, methanol does not have \(\begin{array}{*{20}{c}}{{\rm{OH}}}\\{\rm{|}}\\{{\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{CH – }}}\end{array}\) group and therefore, does not give an iodoform test.

Applications of Iodoform Test

The applications of the Iodoform test is as follows:

1. Iodoform test is used as the for detection of \({\text{C}}{{\text{H}}_3}{\text{CO}} – \) or \({\text{C}}{{\text{H}}_3}{\text{CHOH}} – \) in an organic compound.
2. Iodoform test can be used to distinguish several pairs of compounds.

Iodoform Test is used to distinguish between the following compounds:

S. No.	Pair of Compounds	Compounds that gives positive iodoform test
1	Methanol (Methyl alcohol) and Ethanol (Ethyl alcohol)	Ethanol (Ethyl alcohol)
2	Ethanol (Ethyl alcohol) and propan\( – 1 – {\text{ol}}\) (n-propyl alcohol)	Ethanol (Ethyl alcohol)
3	Propan\( – 1 – {\text{ol}}\) (n propyl alcohol) and propan\( – 2 – {\text{ol}}\) (isopropyl alcohol)	Propan\( – 2 – {\text{ol}}\)(isopropyl alcohol)
4	Butan\( – 1 – {\text{ol}}\) (n-butyl alcohol) and butan\( – 2 – {\text{ol}}\) (sec-butyl alcohol)	Butan\( – 2 – {\text{ol}}\) (sec-butyl alcohol)
5	\(2 – \)methylpropan\( – 1 – {\text{ol}}\)(isobutyl alcohol) and butan\( – 2 – {\text{ol}}\) (sec-butyl alcohol)	Butan\( – 2 – {\text{ol}}\) (sec-butyl alcohol)
6	Methanal (formaldehyde) and Ethanal (Acetaldehyde)	Ethanal (acetaldehyde)
7	Ethanal (acetaldehyde) and propanal (propanaldehyde)	Ethanal (acetaldehyde)
8	Pentan\( – 2 – \)one (methyl propyl ketone) and pentan\( – 3 – \)one (diethyl ketone)	Pentan\( – 2 – \)one (methyl propyl ketone)

Iodoform Uses

The uses of Iodoform are as follows:

I. It is used as an antiseptic. This nature of Iodoform is due to iodine that it liberates and not due to Iodoform itself. However, its very unpleasant smell has now been replaced by other formulations containing iodine.
II. It is used in the manufacture of pharmaceuticals.

Summary

Iodoform is a crystalline pale-yellow material that is highly flammable. It is insoluble in water but soluble in ethyl alcohol and ether. Iodoform has a chemical behaviour that is nearly identical to that of chloroform. The iodoform test detects the presence of an aldehyde or ketone in which a methyl group is one of the groups immediately linked to the carbonyl carbon. It is also used as an antiseptic and in the manufacture of pharmaceuticals, among other uses. The Iodoform tests can also be used to identify several pairs of compounds.

FAQs on Iodoform

Q.1. Is Iodoform the same as iodine?
Ans: Iodoform is not the same as iodine. Iodoform is an organoiodine compound with the formula \({\text{CH}}{{\text{I}}_3}\) and has a tetrahedral molecular geometry. Iodine, on the other hand, is a simple molecule. 

Q.2. Which compounds give the iodoform test?
Ans: Following compounds give the Iodoform test;
a. Ethanol
b. Propan\( – 2 – {\text{ol}}\)
c. Lactic acid
d. Acetaldehyde
e. Methyl ketones

Q.3. Why does Iodoform show antiseptic properties?
Ans: Iodoform shows antiseptic properties due to the iodine that Iodoform liberates. 

Q.4. What is the iodoform packing strip used for?
Ans: Iodoform packing strips are used for sterile drainage open and infected wounds.

Q.5. Describe the structure of Iodoform.
Ans: The iodoform molecule contains \(4\) bonds, of which \(3\) are \({\text{C}} – {\text{I}}\) bonds, and one is a \({\text{C}} – {\text{H}}\) bond.

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