Acetaldehyde - C₂H₄O

What is Acetaldehyde (CH3CHO)?

C₂H₄O is an organic chemical compound with the chemical name Acetaldehyde.

Acetaldehyde is also called MeCHO. It is miscible with napthalene, gasoline, xylene, ether, turpentine, alcohol and benzene. It has no colour and is a flammable liquid. It has a suffocating smell. It is non-corrosive to many metals but when It has a narcotic action and can cause mucous irritation.

Table of Contents

• Acetaldehyde Structure
• Acetaldehyde Formula
• Properties of Acetaldehyde
• Preparations of Acetaldehyde
• Chemical Properties of Acetaldehyde
• Acetaldehyde (C2H4O) Uses
• Acetaldehyde Toxicity
• Frequently Asked Questions – FAQs

Acetaldehyde is widely used in the manufacturing of perfumes, drugs, acetic acid, flavouring agent, dyes, etc. When acetaldehyde is applied externally for prolonged periods it is toxic. Acetaldehyde was first observed in the year 1774 by the Swedish pharmacist/chemist Carl Wilhelm Scheele.

Acetaldehyde Structure (C₂H₄O Structure)

Acetaldehyde Formula

The formula for Acetaldehyde CH₃CHO or C₂H₄O.

Properties of Acetaldehyde – C₂H₄O

Preparation of Acetaldehyde – CH₃CHO

1. Oxidation of Ethyl alcohol

Ethyl alcohol (CH₃CH₂OH) undergoes oxidation in the presence of acidified K₂Cr₂O₇ or aqueous/alkaline KMnO₄ produces acetaldehyde.

\(\begin{array}{l} CH_{3}CH_{2}OH + [O] \overset{oxidation}{\rightarrow} CH_{3}CHO + H_{2}O\end{array} \)

2. Catalytic Dehydrogenation of ethyl alcohol.

Ethyl alcohol undergoes catalytic dehydrogenation in presence of a copper catalyst at 573 K and produces acetaldehyde.

\(\begin{array}{l}CH_{3}CH_{2}OH \overset{Cu/573K}{\rightarrow} CH_{3}CHO + H_{2}\end{array} \)

3. Rosenmund’s Reduction.

Acetaldehyde can be prepared by the reduction of acetyl chloride with H₂ in the presence of palladium deposited over barium sulphate along with a small amount of salt of sulphur or quinoline. This mixture is known as Lindlar’s catalyst. This reaction is called Rosenmund’s Reduction.

\(\begin{array}{l} CH_{3}COCl \xrightarrow[S/quinoline]{Pd/BaSO_{4}}CH_{3}CHO + HCl\end{array} \)

4. By Wacker Process

Ethene can be converted to acetaldehyde by reacting with an aqueous solution containing Palladium chloride and cupric chloride.

\(\begin{array}{l}CH_{2}= CH_{2} + PdCl_{2} + H_{2}O \overset{CuCl_{2}}{\rightarrow}CH_{3}CHO + Pd + 2HCl\end{array} \)

In this reaction, CuCl₂ Converted Pd back into PdCl₂.

2CuCl₂ + Pd → PdCl₂ + 2CuCl

Cuprous chloride is reoxidised to CuCl₂ by atmospheric oxygen in the presence of HCl.

4CuCl + 4HCl +O₂ → 4CuCl₂ + 2H₂O

5. Preparation from Acetylene:

Acetylene gets hydrated in the presence of a mixture of diluted H₂SO₄ and mercuric acid to vinyl alcohol which tautomerises to a more stable compound of acetaldehyde.

CH≡CH + H₂O → CH₂=CHOH → CH₃CHO

Chemical Properties of Acetaldehyde – CH3CHO

1. Acetaldehyde reacts with Hydrazine

The nitrogen atom of phenylhydrazine acts as a nucleophile which attacks the electrophilic carbon of acetaldehyde and removes water to give acetaldehyde phenylhydrazone.

2. Acetaldehyde reacts with HCN

Hydrogen cyanide is added across the carbon-oxygen double bond in aldehydes and ketones to produce compounds known as hydroxynitriles. For example, with ethanal (an aldehyde) you get 2-hydroxypropanenitrile.

3. Acetaldehyde reacts with NaOH

Acetaldehyde (A) reacts when NaOH undergoes aldol condensation forming beta-hydroxyacetaldehyde on heating giving alpha-beta-unsaturated aldehyde.

Acetaldehyde (C₂H₄O) Uses

• It was used as a precursor to acetic acid.
• It is used as a precursor to pyridine derivatives, crotonaldehyde, and pentaerythritol.
• Used in the manufacturing of resin.
• It is used to produce polyvinyl acetate.
• It is used in the manufacturing of disinfectants, perfumes, and drugs
• It is used in the production of chemicals such as acetic acid.

Acetaldehyde Toxicity

Acetaldehyde is a significantly more potent toxin than ethanol, and its first metabolite, acetaldehyde, is responsible for at least a portion of ethanol toxicity. Some of the acetaldehyde gets into your bloodstream, causing damage to your membranes and possibly scar tissue. It also causes a hangover, as well as a racing heart, a headache, and an upset stomach. Acetaldehyde intoxication has the greatest impact on the brain. It impairs memory and causes issues with brain activity.

Based on insufficient human cancer research and animal studies that showed nasal cancers in rats and laryngeal tumours in hamsters, acetaldehyde is classified as a potential human carcinogen. One of the main culprits mediating the fibrogenic and mutagenic effects of alcohol in the liver is acetaldehyde, a significant toxic metabolite. Acetaldehyde stimulates the development of adducts, which causes functional impairments in essential proteins, such as enzymes, as well as DNA damage, which promotes mutagenesis.

Learn more about the Structure, physical and chemical properties of Acetaldehyde from the experts at BYJU’S.

Other related links: