Esterification Reaction In Fragrance Synthesis

Esterification, the reaction in fragrance synthesis, involves the reaction of carboxylic acids/anhydrides with alcohols (or phenols) under catalysis to produce ester fragrances. The aroma of the ester is determined by the structure of the acid and alcohol, and it is a central reaction for natural fragrance substitution and the creation of novel fragrances.

Typical Applications and Representative Fragrances

Fruitful Fragrances: Isoamyl acetate (acetic acid + isoamyl alcohol, banana/pear scent), ethyl butyrate (butyric acid + ethanol, pineapple scent), ethyl hexanoate (hexanoic acid + ethanol, apple/strawberry scent).

Floral Fragrances: Benzyl benzoate (benzoic acid + benzyl alcohol, jasmine/gardenia scent, also has a fixative effect), ethyl cinnamate (cinnamic acid + ethanol, rose/cinnamon scent).

Special Fragrance Types: Ethyl lactate (lactic acid + ethanol, creamy/fruity scent), methyl salicylate (salicylic acid + methanol, wintergreen/mint scent, commonly used in refreshing fragrances).

Synthesis Points

1. Catalyst: Toluenesulfonic acid (mild with fewer side reactions) is preferred over traditional concentrated sulfuric acid to avoid impurities such as alcohol dehydration. Industrially, acid anhydrides (such as acetic anhydride) are also commonly used to improve reaction efficiency, eliminating the need for additional dehydration.

2. Process: "Reflux separation" is often used to remove generated water, shifting the equilibrium to the right and increasing yield. The product is washed and purified by distillation to ensure fragrance and aroma purity.

Taking isoamyl acetate (banana flavor, 500 tons per year) as an example, the equipment parameters and process for industrial mass production are provided, suitable for non-corrosive systems, balancing efficiency and aroma purity:

Equipment List

Esterification Reactor

Fracturing Column

Washing Tank

Plate Distillation Column Vacuum Dryer

Processes (DCS Automatic Control)

1. Feeding: Add acetic acid (1600 kg), isoamyl alcohol (2200 kg), and p-toluenesulfonic acid (30 kg, catalyst) to the reactor, and start stirring;

2. Esterification: Heat to 90-100℃, reflux for 4 hours, separate the generated water (approximately 300 kg) in a fractionation column, and recover the isoamyl alcohol for recycling;

3. Post-treatment: Transfer the reaction solution to a water washing tank, wash twice with deionized water (800 kg each time) to neutralize residual acid;

4. Purification: After water washing, send the material to a distillation column for vacuum distillation, collect the fraction at 85-90℃ to obtain the pure product;

5. Finished Product: After drying, analyze by gas chromatography (purity ≥ 99.2%), and meter and bottle.