General Characteristics of Iodoform

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Introduction to Iodoform

Iodoform is an organoiodine compound having a chemical formula CHI3 and belongs to the organic halogen compound family. It is a substance, a crystalline pale yellow that is volatile in nature. It has a distinctive and penetrating odour with a sweetish smell, which is analogous to chloroform. It was used widely in the hospitals and described as the hospital's smell because of its distinctive odour. Commonly, iodoform is used as an antiseptic component of some medications and as a disinfectant due to its nonirritant action.

Preparation and Properties of Iodoform

Iodoform can be manufactured using the electrolysis of an aqueous solution that contains inorganic iodides, carbonate'>sodium carbonate, and acetone. Iodoform is also referred to as carbon tri-iodide, methyl tri-iodide, and tri-iodomethane. These names are such due to the presence of 3 iodine molecules in the compound. This dressing wound chemical causes a burning sensation when applied to open wounds. Moreover, this compound's molecular weight is given as 393.73 g/mol and a melting point of 121°C. This is a highly pure substance with a purity percentage of 98%, where this value is much higher than most of the other substances. The key features of this compound are given as high purity, effectiveness, balanced composition. It is a very skin-friendly chemical because it does not cause any irritation or itching except that it causes a burning sensation on the open wounds.

Synthesis and Reactions

The synthesis of iodoform compound was first described in 1822 by Georges-Simon Serullas, by the reactions of iodine vapour with the steam over red-hot coals, including the reaction of potassium with the ethanolic iodine compound in the presence of water; and independently by John Thomas Cooper, as well. It can be synthesized using the haloform reaction with sodium hydroxide and iodine reaction with any of these 4 kinds of organic compounds:

  • acetaldehyde (CH3CHO)

  • a methyl ketone (CH3COR)

  • certain secondary alcohols (CH3CHROH, R is either an aryl or alkyl group)

  • ethanol (CH3CH2OH)

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The iodine and base reaction with the combination of methyl ketones is more reliable compared to the iodoform test (which is in yellow precipitate appearance) can be used to probe a methyl ketone presence. This also falls under the case when testing particular secondary alcohols containing at least one methyl group in the alpha position.

A few of the reagents (for example, hydrogen iodide) converts the iodoform to diiodomethane. Besides, converting into carbon dioxide makes it possible when Iodoform reacts with aqueous silver-nitrate'>silver nitrate to form carbon monoxide. When treated with the powdered elemental silver, the iodoform gets reduced, forming acetylene. Moreover, the iodoform compound decomposes to form hydrogen iodide gas, diatomic iodine, and carbon upon heating.

Uses of Iodoform

On a small scale, iodoform can be used as a disinfectant. It was also used as a component in the 20th century in medicines for healing and antiseptic dressing of sores and wounds. It was used for sterilizing the instruments that are used for surgery. There exist many side effects associated with iodoform, and hence its use has now been suppressed with the evolution and adaption of new antiseptics. It is said as an active ingredient for making dog and cat powders along with propanoic acid and zinc oxide, which are used to prevent infection. It can also be used to facilitate the removal of ear hair.

Acetone vs. Methanol

Let us distinguish between the elements Methanol and Acetone in brief.

Acetone produces crystals with NaI (sodium iodide): Add NaI solution, Boil until dissolution, then cool it to -5°C. If we get orange crystals, it is identified as acetone. Also, we need to check the book by Armarego and Perrin on laboratory chemicals purification for the proportions. This is one of the methods to result in water-free acetone.

It is also possible that a few metal salts will provide us with differently coloured complexes, such as cobalt bromide (CoBr2), blue in acetone, and pink in methanol. There is also the fact that ethanol and CoBr2 results in a pink solution, so we can expect methanol to be the same, but it might not be the same case. Probably, CoCl2 can be used as well. It is better to use the dry salts (blue for CoCl2, green for CoBr2), but it might work with the hydrated salts (pink - in both cases).

Iodoform Test for Ketones

Iodoform test is the one that is used to detect ketones and aldehydes that have an alpha-methyl group. Alpha means that it is attached to the carbon, including the functional group. The reagents used here are given as sodium hydroxide (NaOH) and iodine.

The compounds that result in a positive iodoform test are Ethanal (Acetaldehyde), Alpha Methyl groups, and Methyl ketones.

Ethanal is given as the only aldehyde that produces a positive iodoform test. Therefore, aldehyde and ketone with structure -COCH3 also exhibit positive results.

FAQ (Frequently Asked Questions)

Q1. List the Applications of Iodoform?

Ans. The iodoform compound finds small-scale disinfectant use. Nearly at the beginning of the 20th century, this compound was used in medicine as an antiseptic dressing and healing for sores and wounds. However, now this use is superseded by superior antiseptics. It is also described as an active ingredient in several ear powders for both cats and dogs, along with the compounds such as propionic acid and zinc oxide, which are used for infection prevention and facilitate removal of ear hair.

Q2. Distinguish Between Acetone and Ethanol Using an Iodoform Reaction?

Ans. We cannot distinguish acetone and ethanol using an iodoform reaction. Because both these compounds can react with I₂, NaOH and forms a yellow precipitate of CHI₃. This is due to acetone contain CH₃CO⁻ group and ethanol contain the CH₃CH(OH) Group. Therefore, they will result in a positive response to the iodoform test.

We have to react both with a 2, 4- di nitrophenylhydrazine (which is called Brady's reagent). And, acetone will react and form orange precipitate/colour. Whereas ethanol will not react or does not give any precipitate colour with the same Brady's reagent.

Q3. Explain the Iodoform Test?

Ans. Iodoform is described as the organoiodine compound having the formula CHI₃. It is a crystalline, pale yellow, and volatile substance with a distinctive odour and penetrating, which is analogous to chloroform with a sweetish taste.

Q4. Can Alcohol Represent an Iodoform Reaction?

Ans. Yes, alcohol represents an iodoform reaction. It is when alcohol is in such a structure that it undergoes base-catalyzed oxidation to produce ketone.