What is the Difference Between Glacial Acetic Acid and Acetic Anhydride

The key difference between glacial acetic acid and acetic anhydride is that glacial acetic acid is the most concentrated form of acetic acid, whereas acetic anhydride is the dehydrated form of acetic acid.

Acetic acid is an organic compound that is very useful in different organic synthesis reactions. It can be found in its concentrated or pure form, which is named glacial acetic acid. It can also be found in its dehydrated form as acetic anhydride.

CONTENTS

1. Overview and Key Difference
2. What is Glacial Acetic Acid  
3. What is Acetic Anhydride
4. Glacial Acetic Acid vs Acetic Anhydride in Tabular Form
5. Summary – Glacial Acetic Acid vs Acetic Anhydride 

What is Glacial Acetic Acid?

Glacial acetic acid is the concentrated form of acetic acid. Acetic acid is an organic compound having the chemical formula CH3COOH. The molar mass of this compound is 60 g/mol, while the IUPAC name of this compound is Ethanoic acid. Furthermore, at room temperature, glacial acetic acid is a colourless liquid having a sour taste. We can name glacial acetic acid as a carboxylic acid because of the presence of a carboxylic acid group (-COOH).

Moreover, glacial acetic acid has a pungent odour, which is similar to the odour of vinegar and has a characteristic sour taste. It is also a weak acid because it dissociates partially in an aqueous solution, releasing acetate anion and a proton. Generally, acetic acid has one dissociable proton per molecule. However, glacial acid is an irritant that is highly corrosive.

Glacial acetic acid is a simple carboxylic acid; in fact, it is the second simplest carboxylic acid. In the solid-state of this substance, the molecules form chains of molecules via hydrogen bonding. However, in the vapour phase of this compound, it forms dimers (two molecules connected to each other via hydrogen bonds). Since liquid glacial acetic acid is a polar protic solvent, it is miscible with many polar and nonpolar solvents.

What is Acetic Anhydride?

Acetic anhydride is an organic compound having the chemical formula (CH3CO)2O. It is also known as ethanoic anhydride. We can abbreviate it as ac2O. Acetic anhydride is the simplest isolable anhydride compound of a carboxylic acid.

This substance is widely used as a reagent for organic synthesis processes. It occurs as a colourless liquid having a strong acetic acid odour. This strong odour forms due to the reaction between acetic anhydride and moisture in the air.

Similar to most other acid anhydride compounds, acetic anhydride is a flexible compound having a nonplanar structure. It has a pi system linkage that forms through the central oxygen atom, which offers a very weak resonance stabilization than the dipole-dipole repulsion between the two carbonyl oxygen atoms.

We can produce acetic anhydride by heating potassium acetate with benzoyl chloride. Industrially, it is produced by carbonylation of methyl acetate. However, due to its low cost, laboratories usually do not prepare acetic anhydride for research uses; instead, they purchase it from other suppliers.

What is the Difference Between Glacial Acetic Acid and Acetic Anhydride?

We can find acetic acid in its concentrated or pure form, which is known as glacial acetic acid. We can also find it in its dehydrated form as acetic anhydride. The key difference between glacial acetic acid and acetic anhydride is that glacial acetic acid is the most concentrated form of acetic acid, whereas acetic anhydride is the dehydrated form of acetic acid.

The below infographic lists the differences between glacial acetic acid and acetic anhydride in tabular form for side by side comparison

Summary – Glacial Acetic Acid vs Acetic Anhydride

Acetic acid is an organic compound that is very useful in different organic synthesis reactions. The key difference between glacial acetic acid and acetic anhydride is that glacial acetic acid is the most concentrated form of acetic acid, whereas acetic anhydride is the dehydrated form of acetic acid.

Reference:

1. “Acetic Anhydride.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine.

Image Courtesy:

1. “Acetic acid” By W. Oelen – (CC BY-SA 3.0) via Commons Wikimedia
2. “Acetic anhydride2DACS” By Fuse809 – Own work (Public Domain) via Commons Wikimedia