Esters of which acid are used in the perfume industry?

Benzoic acid

The correct answer is option 2. Benzoic acid.

Here is a detailed explanation of why esters of benzoic acid are commonly used in the perfume industry, compared to the other options:

1. Propanoic Acid

Propanoic acid \((CH_3CH_2COOH)\) is a small carboxylic acid. Esters of propanoic acid, such as propyl propanoate, tend to have fruity odors.

Usage: These esters are more commonly used in flavorings rather than perfumes. They do not have the complex aromatic properties desirable in high-quality perfumes.

2. Benzoic Acid

Benzoic acid \((C_6H_5COOH)\) is an aromatic carboxylic acid. Esters such as benzyl benzoate and methyl benzoate.

Benzyl Benzoate: Has a mild, sweet balsamic scent and is used as a fixative in perfumes. Fixatives help to stabilize the volatile components of the fragrance, making it last longer.

Methyl Benzoate: Has a pleasant, sweet, floral scent and is often used in floral perfumes.

Reason for Use:

Aromatic Nature: The benzene ring in benzoic acid gives its esters complex and desirable aromatic properties.

Fixative Properties: Benzyl benzoate, in particular, helps prolong the scent of the perfume by slowing down the evaporation of the more volatile fragrance components.

3. Phthalic Acid

Phthalic acid \((C_6H_4(CO_2H_2))\) is an aromatic dicarboxylic acid. Esters such as phthalates are used primarily as plasticizers.

Usage: Phthalates are more commonly used to make plastics flexible and are generally not used in perfumes due to potential health concerns and their primary application in industrial settings.

4. Formic Acid

Formic acid \((HCOOH)\) is the simplest carboxylic acid.

Esters: Esters such as methyl formate have a somewhat fruity odor.

Usage: These esters are more commonly used as industrial solvents and in flavorings, not in perfumes. Their simple structure does not provide the complex aromas needed for high-quality fragrances.

Conclusion

Esters of benzoic acid are preferred in the perfume industry because:

They have complex, pleasant aromatic properties due to the benzene ring.

Benzyl benzoate serves as an effective fixative, enhancing the longevity of the perfume.

Methyl benzoate adds sweet, floral notes to perfumes.

The other acids listed (propanoic acid, phthalic acid, and formic acid) do not produce esters with the same desirable aromatic properties and are not commonly used in the perfume industry.

Therefore, the correct answer is: Benzoic Acid.