What Is Acetaldehyde? Key Characteristics and Important Uses
It is an organic chemical compound with the chemical name Acetaldehyde. Acetaldehyde is also called MeCHO. It is a colourless organic liquid having a molecular formula C2H4O, also known as CH3CHO. IUPAC name of Acetaldehyde is ethanal. It has a pungent odor.
It is soluble in water and has a suffocating smell. It is non-corrosive to many metals but when it has a narcotic action and can cause mucous irritation. It can damage our liver. When we drink alcohol it breaks and forms Acetaldehyde. It is completely soluble in water.
Acetaldehyde is usually used as an intermediate in the production of acetic acid, also it is used in the manufacturing of perfumes, drugs, flavouring agents, dyes, etc. When Acetaldehyde is applied externally for prolonged periods it is toxic.
Properties of Acetaldehyde- C2H4O or CH3CHO
Molecular weight: 44.05 g/mol
Density: 0.784 g/cm3
Boiling point: 20.2 °C
Melting point: -123.5 °C
Colour: Colourless
Odor: Pungent odor
Solubility: It is soluble in water, ethanol, benzene, acetone, and slightly soluble in Chloroform.
Acetaldehyde Structure(C2H4O-Structure)
C- Carbon, H- Hydrogen, O- Oxygen
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Acetaldehyde (C2H4O OR CH3CHO) Occurrence
Acetaldehyde can be found in many plants and ripe fruits. Also, it is an intermediate in the ethanol metabolism, through the action of enzymes alcohol dehydrogenase that changes ethanol to acetaldehyde.
Uses of Acetaldehyde(C2H4O or CH3CHO)
Acetaldehyde is primarily used to produce other chemicals.
It is used to produce acetic acid.
It is used to manufacture resin.
It is used to manufacture disinfectants, drugs, and perfumes.
It is used to produce polyvinyl acetate.
It is used as a precursor to pyridine derivatives, crotonaldehyde, and pentaerythritol.
Acetaldehyde is also used as a preservative for fruit and fish in the manufacture of vinegar, yeast, etc.
It is used as a solvent in some industrial processes such as the manufacturing of paper, tanning, and rubber.
Also, we use it in the production of n-butyraldehyde.
It is used in leather tanning, as a denaturant for alcohol, in fuel mixtures, as a hardener for gelatin fibres, in glue and casein products.
Solved Examples
1. How to prepare acetaldehyde by dehydrogenation of ethanol?
Solution: Acetaldehyde can be prepared acetaldehyde from the dehydrogenation of ethanol by using copper as a catalyst in this reaction. At 260-28000C, the ethanol reacts over the catalyst to form acetaldehyde:
CH3CH2OH + ½ O2 → CH3CHO + H2O
2. How to prepare Acetaldehyde?
One of the methods of preparation of Acetaldehyde is the hydration of acetylene or ethylene by the Wacker process in which copper or palladium is the catalyst:
2CH2=CH2 + O2 → 2CH3CHO
Acetaldehyde was produced by the hydration of acetylene in which mercury (II) salts serve as a catalyst Before the Wacker process,
C2H2+ H2O + Hg2 → CH3CHO + Hg
Temperature maintained during the reaction is 90-950C, and the formed acetaldehyde is separated from water and mercury and cooled to 25-300C
Oxidation of ethanol is another method where partial dehydrogenation of ethanol produces acetaldehyde in the presence of copper as a catalyst:
CH3CH2OH → CH3CHO + H2
Ethanol vapour is passed at a temperature of 260-2900C in this process.
Fun Facts
Acetaldehyde is a clear liquid that burns easily. Acetaldehyde has a strong fruity odour that in high concentration can make breathing difficult.
If acetaldehyde can be in contact with your eyes, flush them with large amounts of water for at least 15 minutes. Lift the lower and upper lids from time to time. Get medical attention. If acetaldehyde can be in contact with your skin, gently wash the skin with soap and water for 15 minutes. If this does not help, get medical attention.
Acetaldehyde can hurt our heart and blood vessels. Other studies on animals show that breathing acetaldehyde can severely damage the lungs and cause cancer. Repeated exposure to acetaldehyde in the air may cause cancer in humans. When we drink alcohol, our liver transforms acetaldehyde into an acid. It can damage our liver.
It is very interesting that Acetaldehyde is completely soluble in water and tends to form a long chain.
FAQs on Acetaldehyde: Properties, Structure, and Applications
1. What is acetaldehyde and what is its IUPAC name?
Acetaldehyde is an organic chemical compound with the formula CH₃CHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. According to the IUPAC nomenclature system, its official name is ethanal, derived from the two-carbon alkane 'ethane' with the '-al' suffix indicating an aldehyde functional group.
2. What are the key physical and chemical properties of acetaldehyde?
Acetaldehyde exhibits several distinct properties that are important for students to understand. These include:
- Physical Properties: It is a colorless, volatile liquid with a pungent, fruity odor. It is miscible with water, alcohol, and ether in all proportions. Its boiling point is relatively low (20.2 °C), meaning it can be a gas at room temperature.
- Chemical Properties: As an aldehyde, it is highly reactive. It readily undergoes nucleophilic addition reactions, oxidation to form acetic acid (e.g., with Tollen's reagent), and reduction to form ethanol. It also participates in aldol condensation because it possesses alpha-hydrogens.
3. How is the structure of acetaldehyde related to its chemical reactivity?
The structure of acetaldehyde (CH₃CHO) is key to its reactivity. It features a carbonyl group (C=O) where the carbon atom is bonded to a hydrogen atom and a methyl group. The high electronegativity of the oxygen atom polarizes the C=O bond, making the carbonyl carbon electron-deficient (electrophilic) and the oxygen electron-rich. This polarity makes the carbon atom highly susceptible to attack by nucleophiles, which is the characteristic reaction of aldehydes and ketones.
4. What are some of the most important industrial uses and applications of acetaldehyde?
Acetaldehyde is a crucial intermediate in the chemical industry. Its primary application is as a precursor to other chemicals. Important uses include:
- The production of acetic acid through oxidation.
- Synthesis of other organic compounds like ethyl acetate, pyridine derivatives, and pentaerythritol.
- Manufacture of resins, dyes, and perfumes.
- Use as a flavouring agent in foods and as a solvent in industries like rubber and paper.
5. Why is acetaldehyde generally more reactive than ketones like acetone in nucleophilic addition reactions?
Acetaldehyde is more reactive than acetone towards nucleophiles for two main reasons, both rooted in their structure:
- Steric Hindrance: In acetaldehyde (CH₃CHO), the carbonyl carbon is attached to a small hydrogen atom and a methyl group. In acetone (CH₃COCH₃), it is attached to two bulkier methyl groups. These larger groups create more steric hindrance, making it physically more difficult for a nucleophile to approach and attack the carbonyl carbon.
- Electronic Effects: Alkyl groups (like the methyl group, CH₃) are electron-donating. Acetone has two such groups pushing electron density towards the carbonyl carbon, which reduces its positive charge (electrophilicity). Acetaldehyde has only one electron-donating group, making its carbonyl carbon more electrophilic and thus more reactive to nucleophiles.
6. What chemical tests can be used to distinguish between acetaldehyde and formaldehyde?
The most common test to distinguish between acetaldehyde (ethanal) and formaldehyde (methanal) is the Iodoform Test. Acetaldehyde has a methyl group attached to the carbonyl carbon (a methyl ketone structure after oxidation, or simply a CH₃CO- group precursor), which is a requirement for this test. When warmed with iodine and an alkali (like NaOH), acetaldehyde gives a yellow precipitate of iodoform (CHI₃). Formaldehyde, lacking this specific methyl group structure, does not give a positive Iodoform test. Both, however, will give a positive result with Tollen's reagent (silver mirror test).
7. What is the role of acetaldehyde in the human body, particularly after alcohol consumption?
In the human body, acetaldehyde is the primary metabolic byproduct of ethanol (drinking alcohol). The enzyme alcohol dehydrogenase in the liver converts ethanol into acetaldehyde. This compound is highly toxic and carcinogenic, and it is largely responsible for many of the negative effects of alcohol consumption, including hangovers and facial flushing. It is subsequently broken down into less harmful acetate by another enzyme. The buildup of acetaldehyde before it can be processed is what causes cellular damage.
8. Explain why acetaldehyde gives a positive Tollen's test while ketones do not.
Acetaldehyde gives a positive Tollen's test because it is an aldehyde, which can be easily oxidised. The test involves Tollen's reagent, which is an alkaline solution of ammoniacal silver nitrate [Ag(NH₃)₂]⁺. The aldehyde group (-CHO) in acetaldehyde is oxidised to a carboxylate ion (CH₃COO⁻). In this redox reaction, the silver ions (Ag⁺) in the reagent are reduced to metallic silver (Ag), which deposits on the inside of the test tube, forming a characteristic 'silver mirror'. Ketones, like acetone, lack the hydrogen atom directly attached to the carbonyl group and are resistant to oxidation under these mild conditions, hence they do not give a positive Tollen's test.
