What is the Difference Between Acetic Acid and Acetic Anhydride

The key difference between acetic acid and acetic anhydride is that acetic acid is a simple carboxylic acid, whereas acetic anhydride is the dehydration product of acetic acid.

Acetic acid is an organic compound having the chemical formula CH3COOH, while acetic anhydride is an organic compound having the chemical formula (CH3CO)2O. We can use acetic acid to produce acetic anhydride.

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

What is Acetic Acid?

Acetic acid is an organic compound having the chemical formula CH3COOH. It is the second simplest carboxylic acid. This acid occurs as a colourless liquid having a pungent, vinegar-like odour. Furthermore, acetic acid has a distinctive sour taste as well. This compound has a methyl group attached to a carboxylic acid. It is a weak acid because it dissociates partially in an aqueous solution. The molar mass of acetic acid is 60.05 g/mol. The conjugate base of this acid is an acetate ion. Moreover, the systemic IUPAC name of acetic acid is ethanoic acid.

Acetic Acid and Acetic Anhydride - Side by Side Comparison

Figure 01: Skeletal Formula of Acetic Acid

In its solid form, acetic acid forms chains by interconnecting the molecules through hydrogen bonds. In its vapour phase, there are dimers of acetic acid. Furthermore, in its liquid state, it is a hydrophilic protic solvent. At physiological pH conditions, this compound exists in a fully ionized form as acetate. We can produce acetic acid in both synthetic and bacterial fermentation routes. In addition to these, in the synthetic route, acetic acid is produced via methanol carbonylation.

We can produce acetic acid industrially in synthetic routes or via biological routes. For example, we can produce acetic acid through the carbonylation of methanol, and we can produce this acid via fermentation of seeds such as apple cider, using potato mash, rice, etc.

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.

Acetic Acid vs Acetic Anhydride in Tabular Form

Figure 02: Acetic Acid Condensation

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 are the Similarities Between Acetic Acid and Acetic Anhydride?

Acetic acid and acetic anhydride are acidic compounds.
They contain carbonyl carbon atoms.
Both are nonplanar compounds.
They exist as colorless liquids having pungent odor.

What is the Difference Between Acetic Acid and Acetic Anhydride?

Acetic acid is an organic compound having the chemical formula CH3COOH, while acetic anhydride is an organic compound having the chemical formula (CH3CO)2O. The key difference between acetic acid and acetic anhydride is that acetic acid is a simple carboxylic acid, whereas acetic anhydride is the dehydration product of acetic acid.

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

Summary – Acetic Acid vs Acetic Anhydride

Acetic acid and acetic anhydride are important compounds in industries. We can use acetic acid to produce acetic anhydride. The key difference between acetic acid and acetic anhydride is that acetic acid is a simple carboxylic acid, whereas acetic anhydride is the dehydration product of acetic acid.