Acetaldehyde commonly known as ethanal is an organic chemical compound. In addition, it is one of the most important aldehydes that occur in nature widely and produced by industries on a large scale. Naturally, plants produce acetaldehyde and they occur in coffee, bread, and ripe fruit. Commonly, we use it in perfumes and in food as a flavoring agent. Learn Acetaldehyde Formula here.
Acetaldehyde Formula and Structure
The chemical formula of acetaldehyde is CH3CHO or C2H40. The molar mass is 44.053 g mL-1. Also, the acetaldehyde molecule has the usual functional group of an aldehyde H-C=O bound to a methyl group (-CH3), so the acetaldehyde is the second most simple aldehyde after the formaldehyde.
Furthermore, the C atom from the aldehyde has a hybridization sp2, but the methyl group has sp3, thus the molecule has a planar-trigonal together with tetrahedral geometry. Besides, the chemical structure is shown below:
We can find acetaldehyde 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.
Preparation of Acetaldehyde
One of the other method today is the hydration of acetylene or ethylene by the Wacker process in which copper or palladium is the catalyst:
2CH2=CH2 + O2 → 2CH3CHO
Before the Wacker process, acetaldehyde was produced by the hydration of acetylene in which mercury (II) salts serve as a catalyst:
C2H2 + Hg2+ + H2O → CH3CHO + Hg
The reaction is conducted at a temperature of 90-95oC, and the formed acetaldehyde is separated from water and mercury and cooled to 25-30oC.
Another method is the oxidation of ethanol, where partial dehydrogenation of ethanol produces acetaldehyde in the presence of copper as a catalyst:
CH3CH2OH → CH3CHO + H2
In this process, ethanol vapor is passed at a temperature of 260-290oC.
Acetaldehyde Physical Properties
Acetaldehyde appears colorless and has a strong odor liquid. In addition, its boiling point is 20.20C and the melting point is -123oC. the density is 0.784 g mL-1. However, acetaldehyde is soluble in miscible water, ethanol, benzene, acetone, and toluene. Also, it is slightly soluble in chloroform.
Chemical Properties of Acetaldehyde
Its properties are similar to formaldehyde, is an important precursor in organic synthesis, especially as an electrophile. Furthermore, by a condensation reaction, we can gain intermediates such as pentaerythritol (intermediate in explosive manufacture) that we can use in organic synthesis.
Also, we use it to produce hydroxyethyl derivatives through a reaction with a Grignard reagent. Apart from that, acetaldehyde is an important building block that we use in the synthesis of heterocycles, such as imines and pyridines.
Uses of Acetaldehyde
In the chemical industry, it has a variety of applications. Largely we use it in the production of dyes, perfumes, acetic acid and as a flavoring agent. Also, we use it in fuel composition and as a solvent in some industrial processes such as the manufacturing of paper, tanning, and rubber.
A useful resin produces when acetaldehyde combines with urea. Acetaldehyde and acetic anhydride react to produce ethylidene diacetate, a predecessor to vinyl acetate that we use to produce polyvinyl acetate. Also, we use it in the production of n-butyraldehyde. But now they use propylene to generate it.
Safety Hazards and Effects on Health
It is a very toxic liquid. Also, it irritates the mucous membrane. Furthermore, large doses can be fatal can cause respiratory paralysis. In addition, it is highly flammable and can form peroxides. Lastly, acetaldehyde is a carcinogen suspected compound.
Solved Example for You
Question: How to prepare acetaldehyde by dehydrogenation of ethanol?
We can prepare acetaldehyde from the dehydrogenation of ethanol by using copper as a catalyst in this reaction. At 260-2800C, the ethanol reacts over the catalyst to form acetaldehyde:
CH3CH2OH + ½ O2 → CH3CHO + H2O