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Perfume Chemistry
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 Perfumes, fragrances, or scents are al part of our daily lives, often without us even knowing it. Shampoos, soaps, detergents, and food all have scents associated with them. The sense of smell is very important as it helps us enjoy many experiences. For instance, without the sense of smell, eating would be very bland because the taste buds on the tongue can only detect four tastes: salt, sweet, bitter, and sour. The nose can detect seven primary odours: camphorous, musky, floral, pepperminty, ethereal, pungent, and putrid and thus, adds to the taste of the meal. These fragrances are a result of volatile molecules which are given off and detected by the seven types of olfactory receptors in the nose that correspond to each of the primary odours.
Many of the fragrances made into perfumes originate from plants. The fragrance does not just come from the flower as in roses but can also come from other parts such as seeds (cardamon), roots (angelica), wood (sandalwood), bark (cinnamon), and peels (orange). The fragrances are extracted from the plant in the form of essential oils. Methods used for the extraction are often labour intensive, and as yields are low, they have to be repeated many times to obtain large quantities.
Consequently, the natural products are usually in short supply thereby forcing the perfumers (makers of perfumes) to develop synthetic substitutes.
The essential oils contain a variety of molecules often in complicated mixtures. These molecules can have different structures comprising of functional groups. These functional groups classify the molecules as alcohols, ethers, aidehydes, ketones, esters, lactones, castor oil products, terpenes, paraffins, and heterocycles. Of these functional groups, aromatic aldehydes, ketones, heterocycles, and terpenes are considered to be the most important. For many essential oils the fragrance is caused by a six membered ring; however, many essential oils don't have the ring and are still fragrant.
A group of acyclic molecules that are common to many essential oils are the terpenes. Terpenes are molecules that are composed of two units of isoprene. Isoprene is the monomer of natural rubber. Two well known terpenes are citral and menthol. Citral is responsible for the odour of lemons, oranges, limes, and lemon grass whereas menthol is present in the oil of peppermint. Not all of the essential oils are pleasantly fragrant when by themselves. An example is indole which has a foul odour, but is often used to add an interesting character to the perfume as many pleasant smelling oils can make a perfume too sweet.
Once the essential oils are obtained, the perfume artist makes the perfume. The combination is carefully made and studied at various temperatures and pH's to make sure that the desired scent will not change.
Since a change in conditions such as temperature and pH must be taken into account. A change in temperature or pH could alter the molecules in the oil which might change the perfume scent from pleasing to foul. Once the perfume oil is made it is dissolved in a solvent (most commonly ethanol). The percentage of essential oils in the mixture determines whether it is a perfume (20-30% essential oil), cologne (8-15% essential oil) or aftershave (1-3% essential oil).
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