Acetaldehyde: Structure, Synthesis & Chemical Formula

Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

Did you know that the compound acetaldehyde can be found in the environment and the things that we use in our everyday lives? This lesson will introduce you to acetaldehyde, including its structure and chemical formula, as well as how it is synthesized with other chemicals.

What is Acetaldehyde?

Acetaldehyde belongs to the aldehyde family of chemicals; it is also known as ethanal. As a chemical intermediary, acetaldehyde is used to flavor or preserve foods (such as fish or fruit), roast coffee and produce dyes and perfumes. Levels of acetaldehyde can also be found in the body as the liver works to break down alcohol that has been consumed. The structure of this compound consists of an alkyl chain bonded to an oxygen molecule (Diagram 1). The chemical formula for acetaldehyde is CH3CHO, but it can also be expressed as MeCHO, where the Me refers to the methyl group (CH3).

Diagram 1: Chemical Structure of Acetaldehyde
Acetaldehyde Structure

Synthesis of Acetaldehyde

The synthesis of an organic chemical simply refers to the process or steps involved in making a chemical compound. These steps require the use of organic chemical reactions that drive the process of producing a desired substance. Depending on the starting organic chemical, different reactions and catalysts can be used to synthesize acetaldehyde.

Using ethylene as an example, the Wacker-Hoechst reaction aids in the conversion of this compound to form acetaldehyde, while the catalyst, an aqueous metal solution, drives the reaction. This method is commonly used when larger volumes of acetaldehyde are necessary. For smaller quantities, laboratories rely on the oxidation reaction to produce acetaldehyde. We will focus on the latter and use a primary alcohol functional group to synthesize acetaldehyde (Diagram 2).

Diagram 2: Using an oxidation reaction, a primary alcohol can be used to synthesize acetaldehyde
Acetaldehyde Synthesis

Using ethanol as the building block to form acetaldehyde (a), a catalyst containing oxygen must be present to oxidize this primary alcohol. This catalyst (labeled as O) is called the oxidizing agent (b), which means it contains an oxygen atom that seeks to remove hydrogen molecules and gain electrons from another compound. By doing this, the by-product of water is formed (Diagram 3).

For acetaldehyde synthesis, the chemical that assumes the honorary title 'oxidizing agent' of a primary alcohol is a sodium dichromate/sulfuric acid solution (Na2Cr2O7/H2SO4). The oxygen atom used to react with ethanol (b) comes from sodium dichromate (Na2Cr2O7). Sulfuric Acid (H2SO4) is used to ensure that synthesis stops where you want it to stop; that is, at the point where the end product acetaldehyde is made.

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