The Chemistry of Perfumes: From Discovery to Synthesis
Literature Seminar Lensey Hill April 18th, 2006
Introduction: One of the most interesting aspects of fragrance chemistry is its ability to incorporate several different areas of chemistry in its investigations.1 Most perfumists can be considered artists in the preparation of fragrances, combining an almost fantastical creativity with the knowledge found in areas such as analytical, synthetic, and physical chemistry. With the advent of new technologies, the fragrance industry has developed in the last 100 years towards a highly synthetic area of industrial chemistry.2 With interruptions of extraction natural products including weather, disease, politics, and economics, synthetic products in industry are much more favorable.3 A comprehensive review of this subject could in fact fill volumes of books and a large portion of this information will not be presented. The purpose of the paper is to explore the mechanism for sensing fragrant molecules in the body, the use of gas chromatography and mass spectrometry in determining fragrant components, and several examples of synthesizing popular fragrant molecules. Historical Significance: One of the most prolific discoveries in the antiquity era that led to what today is known as fragrance chemistry, was the burning of natural salves and oils to produce incense. This act was preformed as a token of esteem to gods through out many years from the Egyptian to Greek periods.2 The use of natural products to produce aro
mas has escalated from worship practices to a booming industry still in use today. The transformation of incense has evolved as the knowledge from alchemists to chemists has evolved. From the antiquity era to the renaissance era, perfumes were composed strictly of uncharacterized aromatic compounds of flowers and barks of trees. The first synthetic fragrant compounds were developed in the mid 1800’s.2 When chemists discovered that compounds could be synthesized in the lab, the art of perfumery took
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on a whole new perspective. In the mid to late 20th century, the use of gas chromatography and mass spectrometry led to the structural characterization of many fragrant components. With this technology, chemists could synthesize the products which would eliminate natural product extraction and reduce cost for certain fragrant components.2 Recently an interesting focus has been placed upon the mechanism by which odorant molecules are recognized in the brain. Scientists hope that by understanding this biological process, new advances in the fragrance industry can be brought about.2 It wasn’t until the last several decades that the actual mechanism for the sense of smells in the human body began to be investigated.4 Though still not completely understood, the olfactory system has led to the resolution of many new biological compounds and their functions in many mammalian species. T
he Olfactory System: The olfactory system is located in the nose of humans on the roof of the two nasal cavities and is responsible for the recognition of over a thousand different odorant molecules.4 The purpose of this system is to bind odorant molecules to receptor sites that upon bonding release information that is ultimately carried to the brain to trigger the sense of smell. Odorant molecules must exhibit several properties for this process to occur. They must exhibit high vapor pressure, low polarity, surface activity, water solubility, and lipophilicity.4 The strength of this system allows for many odorants to be detected and distinguished at relatively low concentrations. The size of the olfactory region in humans is approximately 2.5 cm2 and encompasses roughly 50 million primary sensory receptor cells. Figures 1 and 2 represent the locations and composition of the olfactory system, respectively.
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Figure 1: Location of the Olfactory System in the Human Brain : Picture taken from reference 4.
Figure 2: The Olfactory System: Picture taken from reference 4. The mechanism by which the odorant molecules activate the recognition to the brain is still currently under investigation. The suggested pathway will be discussed in the seminar to follow. Now that the olfactory system has been introduced, several types of fragrant molecules and their synthesis can be discussed. 4,5
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Common Types of Fragrant Molecules: Since the structural discovery of fragrant compounds, several classes of molecules have emerged. Ironically, not all compounds making up perfumes are pleasant smelling. Often times the molecules have wood and musk-like odors, but when combined with other fragrant components a pleasant fragrant perfume is developed. The compounds are divided into roughly twenty categories of aromas.2 Listed in Table 1 are just are several classes of molecules used in perfume synthesis.1 The volatility of many of the components are used to create the fragrance by way of layers or notes.2 Most perfumes consist of three notes; the top, heart, and base. Top notes are essentially responsible for the initial smell of perfumes and are typically the most volatile compounds. The heart note contains the common components that have some volatility and are responsible for the main aroma of the fragrance, generally lasting several hours. Base notes contain the least volatile compounds and have aromas lasting most of the day.6 Table 1 Odorant Example 1 O Amber H (-) -Ambrox Example 2
reaction schemeO O Karanal
OH
Woody
O Side Product of Iso E Super
Timberol
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