Perfume Ingredient Volatility

The term volatility is usually taken to refer to the speed at which a material evaporates. It is not an exactly defined property, and no universally accepted standards are laid down within the scientific literature. As implied above, the dry-down or evaporation behaviour of even an unsophisticated perfume on a simple solid substrate, such as a paper smelling strip, is complex. Some materials are so volatile that they are lost much more rapidly than other components (within minutes), while materials at the opposite end of the volatility spectrum may remain for a considerable time (weeks or months). However, there 

Let us examine the relationship between boiling point and molecular size more closely. Table 11.1 comprises physicochemical information on a number of materials that are or have been used in the fragrance industry. The data were drawn from a number of sources, and some of the parameters e.g. log P and sp which are described later) were calculated from specific mathematical models, so that slightly different 

RMM = relative molecular mass boiling point is at ca. 760mmHg unless otherwise stated log P = common logarithm of estimated octanol/water partition coefficient (Rekker, 1977) sp = Hildebrand solubility parameter as calculated according to Hoy (Barton, 1985) vapour pressure is at 25 °C Lilial = 2-methyl-3-(4 -r-butylphenyl)pro-panal Cervolide = 12-oxacyclohexadecanolide. 

Perhaps a more direct way to assess volatility is to look at the saturated vapour pressure of an ingredient. Saturated vapour pressure refers to the equilibrium pressure exerted by a substance in a closed system at a specified temperature (the volume of the system must, of course, be greater than that of the substance). Table 11.1 again gives representative values. Consider, for example, the volatile material 1,8-cineole (3), which is utilized in many fresh perfumes and is also commonly found in toothpaste flavours. This material has a vapour pressure of ca. 2mmHg at 25 °C (similar to that of limonene), which in the context of the perfumery world is very high. Most musks have vapour pressures that are three to five orders of magnitude smaller than that of cineole. Vapour pressure is directly related to the mass present in the gas phase, so the fact that musks are perceivable at all to the 

Equation (1) is a useful route to calculating headspace concentrations above a pure substance from vapour pressures c is the gas phase concentration in g 1 1, p° is the saturated vapour pressure in mmHg, and T is the temperature in Kelvin. Equation (2) is the same equation restated in terms of concentration m in mol 1 1 at a temperature of 25 °C for cases where the molecular mass is unknown. These equations derive directly from the ideal gas equation. 

Let us examine the relationship between boiling point and molecular size more closely. Table 11.1 comprises of physicochemical information on a number of materials that are, or have been, used in the fragrance 

Ingredient RMM Boiling point (°C) Vapour pressure (mmHg) sp (MPam) LogP 

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Concretes are prepared by extracting fresh plant material with nonpolar solvents (e.g., toluene, hexane, petroleum ether). On evaporation, the resulting residue contains not only volatile fragrance materials, but also a large proportion of nonvolatile substances including waxy compounds. For this reason, concretes (like pomades) are not completely soluble in alcohol and, thus, find limited use as perfume ingredients. However, they can be employed in the scenting of soaps. 

For the preparation of creams, heat the aqueous phase containing all of the water soluble ingredients to about 70°C, and add this phase to the oil phase which has been similarly heated to 70°C. Mix the two liquids at high temperatures for a few minutes, and cool while stirring. If some volatile ingredients or perfumes are to be added, wait until the cream has cooled to at least 37°C. 

The aromatic, warm, and sweetish odor and taste of the seed, leaves, and stem arises from the presence of a volatile oil that contains anethole p-propenyl phenylmethyl ether, C3H5C6H4OCH3), the derivatives of which (anisole and anisaldehyde) are used in food flavoring, particularly bakery, liqueur, and candy products, as well as ingredients for perfumes. For commercial production of anise oil, the seeds and the dried, ripe fruit of the plant are used. Anise oil. a colorless to pale-yellow, strongly refractive liquid of characteristic odor and taste, is prepared by steam distillation of the seed and fruit. The oil contains choline, which finds use in medicine as a carminative and expectorant. 

A characteristic of organic sulfur compounds, especially volatile (low molecular mass) thiols, is their disagreeable odors. For example, 3-methyl-1-butanethiol and 2-butene-1-thiol are ingredients of a skunk s perfume, and methanethiol or ethanethiol is usually added, in small amounts, to natural gas, which is odorless by itself, so that leaks can be readily detected. The chemical properties of thiols and sulfides differ from those of alcohols and ethers in that thiols are somewhat stronger acids than alcohols and the sulfur atoms of these compounds are considerably more nucleophilic than the oxygen of their analogs. They are excellent nucleophiles in substitution reactions. 

Top notes The most volatile ingredients of an essential oil or perfume. The first smells perceived by the olfactory apparatus. 

The perception of a perfume depends, in the first place, upon the presence of odorant molecules in the air, and upon their nature and concentration. Most perfume starts off life as a liquid comprising a wide variety of molecules and of a known composition. In general, perfumers do not have a corresponding knowledge of the composition of volatiles in the air above such a mixture, except on those occasions where headspace analysis has provided hard analytical data (see Chapter 12). Perfumers therefore have to build up knowledge bases that summarize the olfactory behaviour of hundreds of ingredients under many different circumstances ... 

In summary, the volatility and headspace behaviour of perfume components is broadly comprehensible in terms of molecular interactions, both within products such as shampoos and colognes, and on or within substrates such as cloth or hair. However, the extreme complexity of the interactions, and the number of components invariably present, renders it difficult to predict a priori the headspace compositions in any given situation. Similar comments also apply to the related phenomena of ingredient or perfume fixation and substantivity. Nevertheless, it is possible to ... 

Perfumers divide these various notes into top, middle and bottom or, more in keeping with the industry image, into head, heart and base. These classifications are based on a combination of volatility and impact of ingredients. The head notes are those which are most obvious on opening a bottle of perfume and the citrus notes, for example, fall into this category. The heart are the medium volatility notes which are responsible for the basic character of the perfume and the base notes are the least volatile notes which help to hold the others back and blend them together. The base notes become more obvious after the rest of the perfume has evaporated. A well balanced fragrance will typically have about 25% head, 50% heart and 25% base. Apart from the fruits, all the... 

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