Acetaldehyde
Acetaldehyde frequently referred to as ethanal is an organic chemical compound. In addition, it is one of the most crucial aldehydes that occurs in nature widely and is produced by industries on a large scale. Naturally, plants produce acetaldehyde and they occur in coffee, bread, and ripe fruit. Typically, we use it in perfumes and food as a flavoring agent.
Acetaldehyde was among the earlier natural compounds to be discovered when the Swedish chemist Carl Wilhelm Scheele discovered it in 1774, the same year that he first produced chlorine. A variety of other chemists examined its properties before the German Justus von Liebig decided on the name aldehyde in 1835, which would be changed to acetaldehyde by the 1860s. Von Liebig created the name from ‘alcohol dehydrogenated’, al-de-hyd, reflecting the close relationship between acetaldehyde and ethanol (alcohol).
Prior to people realizing that methanol was a more efficient beginning point, the principal commercial use of acetaldehyde was in the production of acetic acid. Even without this, over a million tons a year of acetaldehyde is still produced as a reagent for making polyvinyl acetate (or PVA), in a version of urea-formaldehyde – the resin utilized in MDF and for adhesives and space-filling insulating foam, and as a beginning point for other resins, varnishes, and even food preservatives.
Structure of Acetaldehyde
The acetaldehyde chemical formula is CH3CHO. Its molar mass is 44.053 g mL-1. The acetaldehyde molecule has the normal functional group of an aldehyde H-C =O bound to a methyl group (- CH3) so acetaldehyde is the 2nd most basic aldehyde after the formaldehyde. The C atom from the aldehyde has a hybridization sp2, but the methyl group has a sp3, hence the particle has a planar-trigonal together with tetrahedral geometry. Its chemical structure is as follows.
Preparation of Acetaldehyde
(i) Laboratory technique
Acetaldehyde is prepared in the laboratory by the oxidation of ethyl alcohol with an acidified sodium dichromate solution.
A mixture of ethyl alcohol and sodium dichromate solution is run into boiling dilute sulphuric acid. Instantly an energetic reaction happens and the acetaldehyde formed in the liquid state is instantly distilled off. This avoids the oxidation of acetaldehyde to acetic acid. Ethyl alcohol stays in the solution until it is oxidized. Pure acetaldehyde is obtained by redistillation. Acetaldehyde can likewise be prepared by the dry distillation of a mixture of calcium salts of formic acid and acetic acid.
(ii) Industrial Method
Acetaldehyde is prepared industrially by air oxidation of ethylene utilizing palladium chloride catalyst with a cupric chloride promoter.
Physical Properties
Acetaldehyde is a colorless, with pungent odor liquid. It’s melting and boiling point is -123 ºC and 20.2 ºC and its density are 0.784 g mL-1. Acetaldehyde is soluble and is miscible in water, ethanol, benzene, acetone, and toluene. It is a little soluble in chloroform.
Chemical Properties
Acetaldehyde, similar to formaldehyde, is an important precursor in organic synthesis, particularly as an electrophile. It can s use condensation responses to obtain intermediates such as the pentaerythritol (intermediate in the explosive manufacture) that can be utilized in organic synthesis.
It is utilized to produce hydroxyethyl derivatives through a response with a Grignard reagent. Furthermore, acetaldehyde is an essential building block really utilized in the synthesis of heterocycles, such as pyridines and imines.
Uses of Acetaldehyde
- It is used in the production of acetic acid, acetic anhydride, n-butanol, ethanol, 2-ethyl-1-hexanol, vinyl acetate, paraldehyde, ethyl acetate, etc.
- It is utilized to make acetaldehyde ammonia utilized as a rubber-accelerator.
- It is used to make chloral hydrate, ethanol trimer, and tetramer. Chloral hydrate and ethanol trimer are both utilized as hypnotic drugs whereas ethanol tetramer is used as a slug poison.
- It is utilized as an antibacterial inhalant in nasal infections.
- It is used in the silvering of mirrors.
- It is used to make phenolic resins and synthetic drugs.
Multiple Choice Questions (MCQs) with Answers
- What is the chemical formula for acetaldehyde?
- A) CH4
- B) CH3OH
- C) CH3CHO
- D) C2H5OH
Answer: C) CH3CHO
- Who discovered acetaldehyde in 1774?
- A) Justus von Liebig
- B) Carl Wilhelm Scheele
- C) Antoine Lavoisier
- D) Robert Boyle
Answer: B) Carl Wilhelm Scheele
- What is the principal commercial use of acetaldehyde historically?
- A) Production of polyvinyl acetate
- B) Synthesis of phenolic resins
- C) Manufacture of acetic acid
- D) Formation of hydroxyethyl derivatives
Answer: C) Manufacture of acetic acid
- Which functional group does acetaldehyde belong to?
- A) Ketone
- B) Alcohol
- C) Aldehyde
- D) Ester
Answer: C) Aldehyde
- What is the hybridization of the carbon atom in acetaldehyde’s aldehyde group?
- A) sp
- B) sp2
- C) sp3
- D) dsp3
Answer: B) sp2
- How is acetaldehyde prepared in the laboratory?
- A) Reduction of ethyl alcohol
- B) Oxidation of ethyl alcohol with acidified sodium dichromate
- C) Condensation of acetic acid and formic acid salts
- D) Dehydration of ethanol
Answer: B) Oxidation of ethyl alcohol with acidified sodium dichromate
- Which industrial method is used for the preparation of acetaldehyde?
- A) Oxidation of ethylene with palladium chloride catalyst
- B) Reduction of ethylene with platinum catalyst
- C) Dehydration of ethanol
- D) Oxidation of methanol
Answer: A) Oxidation of ethylene with palladium chloride catalyst
- What is the boiling point of acetaldehyde?
- A) -78 ºC
- B) 0 ºC
- C) 20.2 ºC
- D) 78 ºC
Answer: C) 20.2 ºC
- In which category of solvents is acetaldehyde slightly soluble?
- A) Non-polar solvents
- B) Aromatic solvents
- C) Polar protic solvents
- D) Polar aprotic solvents
Answer: C) Polar protic solvents
- What is acetaldehyde’s role in organic synthesis?
- A) Catalyst
- B) Reducing agent
- C) Electrophile
- D) Nucleophile
Answer: C) Electrophile
- Which compound is NOT produced using acetaldehyde?
- A) Acetic acid
- B) Ethanol
- C) Vinyl acetate
- D) Hydrochloric acid
Answer: D) Hydrochloric acid
- What is acetaldehyde ammonia used for?
- A) Flavoring agent
- B) Rubber accelerator
- C) Hypnotic drug
- D) Antibacterial inhalant
Answer: B) Rubber accelerator
- In which year did Justus von Liebig decide on the name “aldehyde” for the compound, later changed to acetaldehyde?
- A) 1774
- B) 1835
- C) 1860s
- D) 1900
Answer: B) 1835
- What is the molar mass of acetaldehyde?
- A) 32.04 g/mol
- B) 44.053 g/mol
- C) 58.08 g/mol
- D) 72.06 g/mol
Answer: B) 44.053 g/mol
- What type of geometry does the acetaldehyde molecule have?
- A) Linear
- B) Trigonal pyramidal
- C) Tetrahedral
- D) Planar-trigonal and tetrahedral
Answer: D) Planar-trigonal and tetrahedral
- How is pure acetaldehyde obtained in the laboratory after oxidation?
- A) Filtration
- B) Sublimation
- C) Redistillation
- D) Precipitation
Answer: C) Redistillation
- Which of the following is NOT a physical property of acetaldehyde?
- A) Pungent odor
- B) Solubility in water
- C) Boiling point of 20.2 ºC
- D) Formation of hydroxyethyl derivatives
Answer: D) Formation of hydroxyethyl derivatives
- What is the industrial catalyst used in the air oxidation of ethylene to produce acetaldehyde?
- A) Platinum
- B) Palladium chloride
- C) Rhodium
- D) Nickel
Answer: B) Palladium chloride
- What role does acetaldehyde play in the silvering of mirrors?
- A) Reducing agent
- B) Catalyst
- C) Solvent
- D) Precipitating agent
Answer: A) Reducing agent
- Which drug is NOT derived from acetaldehyde?
- A) Chloral hydrate
- B) Ethanol trimer
- C) Aspirin
- D) Ethanol tetramer
Answer: C) Aspirin
- What is the primary use of acetaldehyde in the production of polyvinyl acetate (PVA)?
- A) Food flavoring
- B) Space-filling insulating foam
- C) Perfumes
- D) Adhesives
Answer: D) Adhesives
Summary: Acetaldehyde – Structure, Preparation, and Uses
Acetaldehyde, also known as ethanal, is a vital organic compound found in nature and widely produced by industries. Discovered in 1774 by Carl Wilhelm Scheele, it gained its name “aldehyde” in 1835 by Justus von Liebig, later changed to acetaldehyde. Historically used in acetic acid production, it remains crucial for various applications, producing over a million tons annually.
Structure: With a chemical formula CH3CHO and a molar mass of 44.053 g/mol, acetaldehyde exhibits a planar-trigonal and tetrahedral geometry.
Preparation:
- Laboratory Technique: Ethyl alcohol oxidation with acidified sodium dichromate results in an energetic reaction, producing acetaldehyde.
- Industrial Method: Industrially prepared by air oxidizing ethylene using palladium chloride catalyst with a cupric chloride promoter.
Physical Properties: Acetaldehyde, a colorless liquid with a pungent odor, has a melting point of -123 ºC, boiling point of 20.2 ºC, and density of 0.784 g/mL. It’s soluble in various solvents, including water, ethanol, benzene, acetone, and toluene.
Chemical Properties: Serving as an important precursor in organic synthesis, acetaldehyde participates in condensation reactions and is crucial for the synthesis of heterocycles such as pyridines and imines.
Uses:
- Production: Utilized in the production of acetic acid, acetic anhydride, n-butanol, ethanol, vinyl acetate, paraldehyde, ethyl acetate, and more.
- Rubber-Accelerator: Used in the production of acetaldehyde ammonia, a rubber accelerator.
- Medical Applications: Used in the production of hypnotic drugs like chloral hydrate and ethanol trimer. Ethanol tetramer serves as a slug poison.
- Antibacterial Inhalant: Applied as an antibacterial inhalant in nasal infections.
- Mirrors: Employed in the silvering process of mirrors.
- Chemical Synthesis: Used in the synthesis of phenolic resins and synthetic drugs.
Acetaldehyde’s versatility makes it a fundamental compound with wide-ranging applications in various industries.