Dhristi JEE 2022-24

What is Iodoform?

Iodoform is a yellow, crystalline solid belonging to the family of organic halogen compounds. It is also known as triiodomethane. What is a halogen, you may ask? Any of the six nonmetallic elements that comprise Group 17 of the periodic table are halogens. Thus, the halogen elements are fluorine, chlorine, bromine, iodine, astatine and Tennessee. Iodoform is an organoiodine compound with the formula – CHl3. It is a pale yellow, crystalline, volatile substance with a penetrating and distinctive odour. The use of iodoform is typical as a disinfectant. 


History of Iodoform

George Simon Serullas first described the preparation of iodoform in the year 1822. The synthesis's display was due to iodine vapour's reactions with steam over red hot coals and potassium response with ethanolic iodine in water. You can prepare Iodoform by electrolysis of aqueous solutions containing acetone, inorganic iodides, and sodium carbonate. Several reagents convert iodoform to methylene iodide – a dense liquid, colourless when pure but usually discoloured by iodine traces – used as a heavy medium in gravity separation processes. The world first discovered iodoform's antiseptic properties in 1880, whence it became an essential medicinal tool. But, currently, it has been replaced by more effective substances.


Characteristics of Iodoform

Let us now understand some characteristics of iodoform.

  • The electrolysis of an aqueous solution containing acetone, inorganic iodides, and sodium carbonate leads to iodoform manufacture.

  • Iodoform is also known as tri-iodomethane. The alternate name is due to the presence of three iodine molecules in the compound.

  • It is an organic iodine chemical and a member of the organic halogen family.

  • Its chemical formula is CHI₃.

  • It is highly inflammable.

  • It is a pale-yellow crystalline substance.

  • It is volatile.

  • Iodoform is used in dressing wounds and causes a burning sensation when applied to wounds.

  • The molecular weight of iodoform is 393.73 g/mol. Its melting point is 121 degrees C.

  • It is a highly pure substance and has a purity percentage of 98 per cent. This value is much higher than most other chemical substances.

  • The salient features of iodoform lie in its balanced composition, high purity and effectiveness.

  • Iodoform is a skin-friendly chemical as it does not cause any itching except when applied to open wounds.


Chemical Structure of Iodoform

The chemical structure refers to the arrangement of atoms and the chemical bond that holds the atoms together. Let us try to analyze the chemical structure of iodoform. Iodoform possesses a tetrahedral molecular geometry in which there are 4 bonds present in the iodoform molecule. Out of these 4 bonds, one is the C-I bond and the other is the C-H bond. At the centre of the four substituents that are situated at the tetrahedron’s corners, there is a central atom present in the tetrahedral molecular geometry.


The iodoform molecule contains a total of four bonds. There are three non-H bonds. The 2D chemical structure image of iodoform is also known as the skeletal formula, which is the standard notation for organic molecules. The carbon atoms in the iodoform's chemical structure are located at the corners, and there is no representation of hydrogen atoms attached to the carbon atoms. You can consider that each carbon atom is associated with enough hydrogen atoms to provide the carbon atom with four bonds. 


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The 3D chemical structure of the iodoform is based on the ball and stick model that displays both the atoms' three-dimensional portions and the bonds between them. Therefore, the spheres' radius is smaller than the rod lengths to provide a lucid view of the atoms and bonds within the structural model of the iodoform.


Uses of Iodoform 

There are numerous uses of iodoform, and we have compiled a list for you.

  1. Iodophors is most typically used in the hospitals and it has many other uses as well which are listed below-

  • It is used as an antiseptic to treat minor skin conditions.

  • It is used in a variety of disinfectant products.

  • It is used in products that are used for cleaning polarized films such as LCDs and LEDs.

  • It possesses antiseptic properties and is therefore medically important. 

  1. On a small scale, iodoform's use is that of a disinfectant. During the 20th century, the use of iodoform as a medicine component for healing and dressing wounds and sores was widespread.

  2. Sterilization of surgical instruments was done by using an iodoform.

  3. It is an active ingredient for making cat and dog powders and zinc and propanoic acid to prevent infection.

  4. Iodoform also helps in removing ear hair for dogs and cats.

  5. The angel’s bonnet mushroom contains natural iodoform and displays its characteristic odour. 

Owing to specific side effects, there has been an avoidance of using iodoform as an antiseptic, and advanced alternatives are now available.


The Iodoform Reaction 

So far, we have grasped the concept of iodoform, its structure and its properties. But, now the question is what an iodoform reaction is? Let us try to get the answers. 


An iodoform reaction is a chemical reaction wherein methyl ketone is oxidized to a carboxylate by reaction with aqueous hydroxide and iodide. The iodoform reaction identifies a CH2CH2 (OH) group in alcohols. When you add iodine and sodium hydroxide to a compound that contains either a methyl ketone or secondary alcohol with a methyl group in the alpha position, there is the formation of a pale yellow precipitate of iodoform. You can use it to identify a CH3CH=0 group. Specific compounds that give positive iodoform tests are – Acetaldehyde, Methyl Ketones, Ethanol, etc.


Iodoform Test- Reaction

The iodoform reaction occurs when methyl ketone is reacted in the presence of hydroxide ions with iodine resulting in a carboxylate ion and a haloform. This reaction can be used for the identification of aldehydes and ketones. The only aldehyde that undergoes the haloform reaction is acetaldehyde as it is the only aldehyde with a CH₃C=O group.


Iodoform Reagent

In chemistry, a reagent is a substance added to a system to get a chemical reaction or added to test if a reaction has occurred. There exist two iodoform reagents to check the iodoform reaction.

  1.  Iodine and Sodium Hydroxide Solution 

The iodine solution is added to a small amount of alcohol, accompanied by just enough sodium hydroxide solution to remove the colour of the iodine. The appearance of a very pale yellow residual of iodoform indicates a positive result. You can also recognize the correct deposition by its colour and ‘medical’ smell.

  1.  Potassium Iodide and Sodium Chlorate (I) Solutions 

There is an addition of potassium iodide solution to a small amount of alcohol, followed by sodium chlorate (I). If there is no precipitation, it may be necessary to warm the mixture gently. The positive result is a pale yellow precipitate.


Conclusion

Learning about iodoform is an integral part of chemistry. It is a substance with numerous everyday usages. Hence, the knowledge of iodoform, the reaction of iodoform, etc., has immense academic and practical value.

FAQs on Iodoform

1. What are some of the applications of the iodoform test?

Some of the applications of the iodoform term are listed below-

  • It is used to detect the presence of CH3CO- or CH3CHOH- in organic compounds.

  • It can also be used to distinguish several pairs of compounds such as methanol and ethanol, ethanol and propane-1-ol, propane-1-ol and propane-2-ol, butan-1-ol and butan-2-ol, 2-methyl propane-1-ol and butan-2-ol, methanol and ethanol, ethanal and propanal, pentane-2-one and pentane-3-one.

2. What is the mechanism for the iodoform test?

The removal of the acidic alpha hydrogen is done in the iodoform test by the hydroxide ion. After this, there is a formation of the enolate ion. Then the enolate anion is displaced from the iodine molecule as an iodide ion. This method is repeated thrice to obtain R-CO-Cl3. To the carbonyl carbon, a hydroxide ion is bonded. The Cl3- anion is eliminated and the carbonyl group is reformed as a result. The R-COOH group is also formed and the carboxylic acid group and the Cl3- ion cancel each other out.


To learn more about the mechanism in detail students can visit Vedantu.

3. How is Iodoform prepared?

When ethanol and propanone are heated with alkali and iodine, the compound formed is referred to as iodoform, and the reaction by which it is formed is known as the haloform reaction. 

  • When ethanol is heated in the presence of alkali NaOH and Na2CO3 with iodine at about 60°, iodoform is produced.

  • When propanone is heated in the presence of alkali NaOH and Na2CO3 with iodine, iodoform is produced.

4. How is the Iodoform test performed and what are its indications?

To perform an iodoform test, three drops of the compound that is to be tested are added into 3 ml of water along with 10 drops of KI/I₂ solution. The KI/I2 is a dark purple-brown solution in which 10% NaOH solution is added dropwise till the colour of the solution fades from dark to yellow. Then the solution is heated at a temperature of 60° C and in case the solution becomes colourless more KI/I2 solution is added. If yellow precipitates are formed or there is a suspension of iodoform, it indicates a positive test.

5. What are some of the compounds that give positive iodoform tests?

Some of the compounds that give an iodoform positive test are listed below-

  • Ethanol

  • Methyl Ketones

  • Acetaldehyde

  • Secondary Alcohols in which Methyl Groups are present in the Alpha position.

6. Is the Concept of Iodoform Complicated to Understand?

Nothing is too complicated with perseverance and dedication. With the right kind of preparation, grasping the concept of iodoform becomes reasonably manageable. A thorough understanding of what iodoform is, its structure, along the chemical reaction is crucial. Regular revision and solving past question papers are of tremendous help, as well.


Furthermore, you can also take the aid of Vedantu’s concept pages that are, indeed, a granary of knowledge. The exciting part is that you can read them from the comfort of your home. Moreover, watching educational videos is another way to learn about the iodoform concept quickly.

7. What is the Use of the Iodoform Test, and How is it Done?

The primary use of the iodoform reaction is to test the presence of methyl ketone. You can do the iodoform test by taking ten drops of Kl/IW solution for every 3 ml of water. Three drops of the evaluated compound are also applied. Until the dark brown colour of the solution gives way to a pink colour, 10 percent NaOH solution is used dropwise.

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