What are the two methods of preparation of acetic acid?

What is Acetic Acid?

Acetic acid is an organic compound with the formula CH3COOH. It is a carboxylic acid consisting of a methyl group that is attached to a carboxyl functional group. The systematic IUPAC name of acetic acid is ethanoic acid and its chemical formula can also be written as C2H4O2. Vinegar is a solution of acetic acid in water and contains between 5% to 20% ethanoic acid by volume. The pungent smell and the sour taste is characteristic of the acetic acid present in it.

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An undiluted solution of acetic acid is commonly referred to as glacial acetic acid. It forms crystals which appear like ice at temperatures below 16.6oC. It has a wide range of applications as a polar, protic solvent. In the field of analytical chemistry, glacial acetic acid is widely used in order to estimate substances that are weakly alkaline.

Preparation of  Acetic acid-CH3COOH

Acetic acid is produced industrially via the carbonylation of methanol. The chemical equations for the three steps involved in this process are provided below.

• CH3OH (methanol) + HI (hydrogen iodide) ' CH3I (methyl iodide intermediate) + H2O
• CH3I + CO (carbon monoxide) ' CH3COI (acetyl iodide)
• CH3COI + H2O ' CH3COOH (acetic acid) + HI

Here, a methyl iodide intermediate is generated from the reaction between methanol and hydrogen iodide. This intermediate is then reacted with carbon monoxide and the resulting compound is treated with water to afford the acetic acid product. It is important to note that a metal carbonyl complex must be used as a catalyst for step 2 of this process.

Other Methods of Preparing Acetic Acid

Some naphthalene salts of cobalt, chromium, and manganese can be employed as metal catalysts in the oxidation of acetaldehyde. The chemical equation for this reaction can be written as:

O2 + 2CH3CHO ' 2CH3COOH

Ethylene (C2H4) can be oxidized into acetic acid with the help of a palladium catalyst and a heteropoly acid, as described by the following chemical reaction.

O2 + C2H4 ' CH3COOH

Some anaerobic bacteria have the ability to directly convert sugar into acetic acid.

C6H12O6 ' 3CH3COOH

It can be noted that no ethanol intermediates are formed in the anaerobic fermentation of sugar by these bacteria.

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