General Characteristics of Iodoform

Dhristi JEE 2022-24

Introduction

The organic iodine substance iodoform (also known as triiodomethane and, incorrectly, carbon triiodide) has the formula \[CHI_{3}\]. It is a pale yellow, crystalline, volatile chemical with a deep and characteristic odour (the scent is frequently referred to as that of hospitals, where the compound is still commonly employed) and a sweetish taste, similar to chloroform. It's sometimes used as a disinfectant.


Applications of Iodoform

The chemical is used as a disinfectant on a modest basis. It was employed in medicine as a healing and antiseptic treatment for wounds and sores around the turn of the twentieth century, but superior antiseptics have since supplanted it. Along with zinc oxide and propionic acid, it is the active ingredient in many ear powders for dogs and cats, which intend to prevent infection as it makes hair removal easier.


Background of Iodoform

Iodoform is a tetrahedral molecular geometry organoidine molecule with the formula \[CHI_{3}\]. It's a yellow solid that's generally insoluble in water and chemically reactive in free-radical processes. Minimal quantities of iodoform may be found in disinfectants due to its antibacterial effects upon topical treatment, and it is mostly utilized for veterinary purposes. Due to its radiopacity, iodoform has also been detected in dental paste and root canal filling materials in combination with other intracanal drugs. Iodoform has been used as a healing and antiseptic dressing or powder for wounds and sores since the turn of the twentieth century, although the clinical application has been limited to this point. When it is in touch with secretions or endodontic infections, iodoform is soluble in fatty acids and decomposes, releasing iodine in its initial stage.


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.


FAQs on General Characteristics of Iodoform

1. List the applications of Iodoform?

The iodoform compound finds small-scale disinfectant use. Near 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. 

2. Distinguish between acetone and ethanol using an Iodoform reaction?

We cannot distinguish acetone and ethanol using an iodoform reaction. Because both these compounds can react with \[I_{2}\], NaOH and form a yellow precipitate of \[CHI_{3}\]. This is due to acetone containing \[CH_{3}CO^{-}\] group and ethanol-containing the \[CH_{3}CH(OH)\] Group. Therefore, they will result in a positive response to the iodoform test.


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


Hence its use has now been suppressed with the evolution and adaptation of new antiseptics. It is said to be 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.

3. What are the synthesis and reactions of Iodoform?

Georges-Simon Serullas initially detailed the synthesis of iodoform in 1822, using interactions of iodine vapor with steam over red-hot coals, as well as a reaction of potassium with ethanolic iodine in the presence of water; and John Thomas Cooper did so almost simultaneously. It's made by reacting iodine and sodium hydroxide with any of these four chemical compounds: methyl ketone (\[CH_{3}COR\]), acetaldehyde (\[CH_{3}CHO\]), ethanol (\[CH_{3}CH_{2}OH\]), and some secondary alcohols in the haloform reaction.


The iodine and base reaction with methyl ketones is so reliable that the iodoform test (a yellow precipitate) is used to check for the presence of a methyl ketone. When looking for certain secondary alcohols with at least one methyl group in the alpha position, this is also true.


Iodoform is converted to diiodomethane by some chemicals (for example, hydrogen iodide). Iodoform can also be converted to carbon dioxide when it combines with aqueous silver nitrate to produce carbon monoxide. Iodoform is reduced and acetylene is produced when it is treated with powdered elemental silver. Iodoform decomposes into hydrogen iodide gas, diatomic iodine, and carbon when heated.

4. What are the toxicity levels of Iodoform?

In rats, the oral LD50, dermal LD50, and inhalation LC50 are 355 mg/kg, 1184 mg/kg, and 165 ppm/7h, according to MSDS. In humans, a fatal dose of iodoform is believed to be 2g. Excess absorption through wounds and abscesses, or ingestion of large quantities, can cause systemic intoxication and severe poisoning, which is characterized by dermatitis, headache, somnolence, delirium, hallucinations, consciousness disturbances, vomiting, coma, tachycardia, CNS depression, and rapid feeble pulse.  Although there is no known antidote for iodoform poisoning, supportive and symptomatic care is strongly advised. 


Iodoform poisoning has been linked to hepatocellular damage, with the development of fatty liver and necrosis, as well as lesions of liver membrane cellular components. Iodoform, like carbon tetrachloride, causes hepatocellular damage and hepatic lesions, with cellular membranes possibly being the principal sites of action.

5. What is the mechanism of action in Iodoform?

While the exact mechanism of action of iodoform is unknown, it is thought that it releases iodine, which then oxidizes to denature bacterial proteins. Iodoform may also play a role in chemical debridement to heal necrotic wounds successfully and repair tissue damage via collagen fibrinolysis; iodoform reduces the size of macromolecules containing collagen I in wound surface proteins after treatment in necrotic tissue. High quantities of iodoform were found to inhibit the survival of macrophages and epithelial cells in human gingival fibroblasts in vitro, as well as the secretion of P. gingivalis-induced TNF. P. gingivalis is an anaerobic bacteria that can be found in anaerobic oral environments such as the periapical sites and periodontal pockets. The Vedantu app and website contain free study materials.

6. Explain the Iodoform Test?

Iodoform is described as the organoiodine compound having the formula \[CHI_{3}\]. It is a crystalline, pale yellow, and volatile substance with a distinctive odour and penetrating, which is analogous to chloroform with a sweetish taste.

7. Can Alcohol Represent an Iodoform Reaction?

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

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