ISOAMYL ACETATE: STRUCTURE, PROPERTIES, SYNTHESIS AND USES - CHEMISTRY - 2024

The isoamyl acetate is an ester whose molecular formula is CH ₃ COO (CH ₂) ₂ CH (CH ₃) ₂. At room temperature it consists of an oily, clear, colorless, flammable and volatile liquid. In fact, it is too volatile and fragrant an ester.

Its main characteristic is to give off an odor that contributes to the aroma of many fruits, especially those of the banana or plantain. Likewise, this last fruit constitutes one of its natural sources par excellence.

Bananas, whose characteristic aroma is due to isoamyl acetate. Source: Pixabay.

Hence the name of banana oil that is given to a solution of isoamyl acetate, or to a mixture of isomyl acetate with nitrocellulose. The compound is widely used as a flavoring for food, ice cream, and candy.

In addition, it is used in the production of fragrances with different uses. It is also a solvent used in the extraction of metals and organic compounds such as acetic acid.

Isoamyl acetate is the result of the esterification of isoamyl alcohol with acetic acid. In organic chemistry teaching laboratories, this synthesis represents an interesting experience to implement esterification, while flooding the laboratory with banana fragrance.

Structure of isoamyl acetate

Structure of isoamyl acetate. Source: Ben Mills

The upper image shows the molecular structure of isoamyl acetate using a spheres and bars model. The red spheres correspond to oxygen atoms, specifically those that identify this compound as an ester; its ether portion, ROR, and the carbonyl group, C = O, then having the structural formula R ^' COOR.

On the left, R ^', is the isopentyl alkyl radical, (CH ₃) ₂ CHCH ₂ CH ₂; and to the right, R, to the methyl group, to which the 'acetate' of the name of this ester is owed. It is a relatively small ester, capable of interacting with the chemical receptors of smell in our noses, causing signals that the brain interprets as fragrance.

Intermolecular interactions

The isoamyl acetate molecule itself is flexible; However, the isopentyl radical does not benefit intermolecular interactions because it is branched, sterically preventing the oxygen atoms from interacting efficiently through dipole-dipole forces.

Also, these two oxygen cannot accept hydrogen bonds; structurally the molecule has no way to donate them. Compared with interrupted dipoles, isoamyl acetate can interact intermolecularly by means of London dispersion forces; which are directly proportional to its molecular mass.

This being the case, it is the molecular mass of the ester that is responsible for its molecules forming a liquid with a high boiling point (141 ° C). Likewise, it is responsible for its solid melting at a temperature of -78 ° C.

Banana fragrance

Its intermolecular forces are so weak that the liquid is volatile enough to permeate its surroundings with banana odors. Interestingly, the sweet smell of this ester can change if the number of carbons is reduced or increased.

That is to say, if instead of having six aliphatic carbons it had five (with the isobutyl radical) its smell would resemble that of raspberries; if the radical were secbutyl, the odor would be loaded with traces of organic solvents; and if it had more than six carbons, the smell would start to turn soapy and metallic.

Properties

Chemical names

-Isoamyl acetate

-Isopentyl ethanoate

-3-methylbutyl acetate

-Isopentyl acetate

-Banana or plantain oil.

Molecular formula

C ₇ H ₁₄ O ₂ or CH ₃ COO (CH ₂) ₂ CH (CH ₃) ₂

Molecular weight

130.187 g / mol.

Physical description

It is an oily, clear and colorless liquid.

Odor

At room temperature it has an intense and pleasant banana smell.

Taste

It has a flavor similar to that of pear and apple.

Boiling point

124.5 ° C.

Melting point

-78.5 ° C.

ignition point

Closed cup 92ºF (33ºC); open cup 100ºF (38ºC).

Water solubility

2,000 mg / L at 25 ° C.

Solubility in organic solvents

Miscible with alcohol, ether, ethyl acetate, and amyl alcohol.

Density

0.876 g / cm ³.

Vapor density

4.49 (in relation to air = 1).

Vapor pressure

5.6 mmHg at 25 ° C.

Auto ignition temperature

680 ° F (360 ° C).

Viscosity

-1.03 cPoise at 8.97 ºC

-0.872 cPoise at 19.91 ° ​​C.

Heat of combustion

8,000 cal / g.

Odor threshold

Air = 0.025 µL / L

Water = 0.017 mg / L.

Refractive index

1,400 at 20 ° C.

Relative evaporation rate

0.42 (relative to butyl acetate = 1).

Dielectric constant

4.72 at 20 ° C.

Storage

Isoamyl Acetate is a flammable and volatile compound. Therefore, it should be stored cold in completely airtight containers, away from combustible substances.

Synthesis

It is produced by the esterification of isoamyl alcohol with glacial acetic acid, in a process known as Fisher's esterification. Sulfuric acid is commonly used as a catalyst, but also p-toluenesulfonic acid catalyzes the reaction:

(CH ₃) ₂ CH-CH ₂ -CH ₂ CH ₂ OH + CH ₃ COOH => CH ₃ COOCH ₂ -CH ₂ -CH ₂ -CH (CH ₃) ₂

Applications

Food and beverage flavoring

It is used to impart a pear flavor in water and in syrups. It is used in China to prepare fruit flavors, such as strawberry, blackberry, pineapple, pear, apple, grape, and banana. The doses used are: 190 mg / kg in confectionery; 120 mg / kg in pastry; 56 mg / kg in ice cream; and 28 mg / kg in soft drinks.

Solvent and thinner

It is a solvent for:

-Nitrocellulose and celluloid

-Water proof varnishes

-Ester gum

-Vinyl resin

-Coumarone resin and castor oil.

It is used as a solvent for the determination of chromium and is used as an extraction agent for iron, cobalt and nickel. It is also used as a thinner for oil paints and old lacquers. In addition, it is used in the manufacture of nail polish.

This ester is used as a diluent in the production of acetic acid. Petroleum is used as a raw material in an oxidation process that produces an aqueous solution of acetic acid and other compounds, such as formic acid and propionic acid.

As a solvent and carrier for other substances, it was used in the early days of the aeronautical industry to protect the fabrics of aircraft wings.

Fragrances

-It is used as an air freshener to cover up bad smells.

-It is used as a perfume in the lacquer of the shoes.

-To test the efficiency of gas masks, since isoamyl acetate has a very low odor threshold and is not very toxic.

-It is used in the elaboration of fragrances such as Cyprus; the soft-scented osmanthus; the hyacinth; and the strong oriental flavor, being used in low doses, less than 1%.

Others

It is used in the manufacture of silk and artificial pearls, photographic films, waterproof varnishes and bronzers. It is also used in the textile industry in dyeing and finishing. It is used in the dry cleaning of clothing articles and cloth furniture.

In addition, isoamyl acetate is used in the production of rayon, a synthetic fabric; in the extraction of penicillin, and as a standard substance in chromatography.

Risks

Isoamyl Acetate can irritate the skin and eyes on physical contact. Inhalation can cause irritation to the nose, throat and lungs. Meanwhile, exposure to high concentrations can cause headache, drowsiness, vertigo, dizziness, fatigue and fainting.

Prolonged contact with the skin can cause it to become dry and cracked.

References

1. Bilbrey Jenna. (July 30, 2014). Isoamyl acetate. Chemistry World by The Royal Society of Chemistry. Recovered from: chemistryworld.com
2. National Center for Biotechnology Information. (2019). Isoamyl acetate. PubChem Database. Recovered from: pubchem.ncbi.nlm.nih.gov
3. Wikipedia. (2019). Isoamyl acetate. Recovered from: en.wikipedia.org
4. Royal Society of Chemistry. (2015). Isoamyl acetate. Chemspider. Recovered from: chemspider.com
5. New Jersey Department of Health and Senior Services. (2005). Isoamyl acetate.. Recovered from: nj.gov
6. Chemical Book. (2017). Isoamyl acetate. Recovered from: chemicalbook.com