Perfume chemical stability

The chemical stability of any perfume material in any base depends upon its chemical structure and the composition of the base. General observations about the chemical stability of perfume materials as related to their chemical structure are to be found in Chapter 16. 

Heat is a form of energy that affects the rate at which chemical reactions take place. The shelf life of a product can therefore be considerably reduced by exposure to elevated temperatures. Odor deterioration and discoloration will develop much faster under these conditions, and this is exploited in the accelerated testing of perfumes for stability in final products. Some products are manufactured at quite high temperatures, and perfumers have to keep this in mind in the formulation of their fragrances. 

A perfume needs to fulfill certain technical requirements, such as chemical stability in use. 

In detergent perfumes, the stability of vanillin is not always certain. It depends on the association made with other raw materials, eg, with patchouli, frankincense, cloves, most of the animal notes, and such chemicals as amyl salicylate, methyl ionones, heliotropin, gamma undecalactone, linalool, methyl anthranilate, benzyl acetate, phenyl ethyl alcohol, cedar wood derivatives, oak mosses, coumarin, benzoin, Pem balsam, and cistus derivatives. In some... 

It is known that as soon as a perfume is incorporated into a product matrix, pronounced effects occur on some ingredients, those for which the microenvironmental interactions have changed significantly. Physicochemical interaction is a consideration no matter what the base, whereas chemical interactions only become really important in consumer products possessing a reactive challenge for fragrance, for example products with low or high pH (e.g. below 4, above 9), or redox power (e.g. cold wave hair products or laundry bleaches). (Chemical stability issues are elaborated in Chapter 9.)... 

The two primary aspects of odour are character and intensity. Perfumers are also interested in properties such as tenacity and performance but these are derivative properties combining intensity with physical and chemical properties such as volatility, surface recognition/adhesion, chemical stability in the perfumed medium, Raoult s law deviations and so on. In order to study any phenomenon, it is important to be able to measure it. Unfortunately, both odour character and intensity are very difficult to measure. Odour is a phenomenon that exists only in the higher brain and must therefore be measured using psychological techniques. Moreover, it is highly subjective, even to the point where it would appear that each of us has a unique odour perception of the world around us, as will be explained later. 

Cyclodextrin inclusion compounds have found application in pharmacology, the food industry, and cosmetics. Typical examples are the solubilization of insulin and steroids, the removal of cholesterol from egg yolk, and the conservation of basis notes in perfumes by slow release rates of rose oil and similar ingredients. Chemical stabilization of oxygen-sensitive compounds, e.g., the sulfides of onions and garlic flavor, and of vitamins is also achieved by cyclodexteins. 

Further progress can be easily envisaged. For example, attempts to create perfumes based on suspended capsules go back to the early 1970s. Now formulation in water of sol-gel-entrapped perfumes of tunable scent to avoid skin irritation becomes possible. Stabilized natural fragrances replacing toxic synthetic musks are also forecasted herein. In particular, sol-gel microencapsulated essential oils will replace nonbiodegradable musks as a consequence of the chemical and physical stabilization of nice fragrances that thus far could not be widely commercialized due to weU-known poor chemical stability. 

As a pharmaceutical, methyl salicylate is used in liniments and ointments for the relief of pain and for rheumatic conditions. As a flavor and fragrance agent, it is used in confectioneries, dentifrices, cosmetics, and perfumes. Other commercial applications for methyl salicylate are as a dye carrier, as a uv-light stabilizer in acrylic resins, and as a chemical intermediate. The May 1996 price was 5.50/kg (18). 

Nearly all of the benzal chloride produced is consumed in the manufacture of benzaldehyde. Benzaldehyde (qv) is used in the manufacture of perfume and flavor chemicals, dyes, and pharmaceuticals. The principal part of benzotrichloride production is used in the manufacture of benzoyl chloride (see Benzoic acid). Lesser amounts are consumed in the manufacture of benzotrifluoride, as a dyestuff intermediate, and in producing hydroxybenzophenone ultraviolet light stabilizers. Benzotrifluoride is an important intermediate in the manufacture of herbicides, pharmaceuticals, antimicrobial agents, and the lampreycide, 4-nitro-3-(trifluorometh5l)phenol [88-30-2]. 

The cross-dimerization reaction is very commonly employed for the manufacture of intermediates for synthetic musks, which have become an important class of perfumery chemicals. Synthetic musks have been the target of extensive research over the years due to a conservation order placed on the musk deer. Nitro musks are being steadily replaced by non-nitro polycyclic musks becau.se of technical drawbacks and health aspects of the former, which are explosive, sensitive, and virtually nonbiodegradable. Non-nitro musks, on the other hand exhibit better stability to light and alkali, and more nearly duplicate the odour of the macrocyclic musks occurring in nature. Indian musk odorants are easily soluble in alcohol and perfume compositions. They have the added advantage of non-discoloration in soap and domestic products. In view of the low price, their future in the perfume industry appears very promising. 

Stannic chloride, SnCLp a fuming liquid, is used in the preparation of organic compounds and chemicals to weight silk and to stabilize perfumes and colors in soap. 

Approximately 50% is used as starting material for insecticides, 35-40% for perfumes and drugs and 10-15% for polymerization inhibitors and other chemicals. Catechol has also been used as an antiseptic, in photography, dyestuffs, electroplating, specialty inks, antioxidants and light stabilizers, and in organic synthesis (Hamamoto Umemura, 1991 Lewis, 1993). 

In this section we will consider in a general way some factors that affect the stability of perfume materials in products. Since most changes in odor during product storage are due to chemical interactions between perfume materials and components of the product base, we will look at these interactions first. Color changes will be covered in a separate subsection. Finally, we will look briefly at perfume changes caused by physical factors. 

The majority of the reactions leading to perfume instability are known and understood. Hence the degree of stability of a given perfume in a given medium is, in theory, predictable. In practice, however, a great deal of hard-to-foresee factors may intervene due to the chemical and physical complexity of perfumes and of product bases. Therefore consideration of the chemistry involved is helpful in pinpointing likely... 

Practical aging tests of the finished perfume in the finished product base must be conducted to ascertain perfume stability in each concrete case. These tests are normally conducted at elevated temperatures (40°-45°C), since chemical reactions take place more quickly at higher temperatures. 

The odor, volatility, strength, and stability of the materials used in perfumery are all determined by their chemical structure. It is useful therefore, and of interest, for the perfumer to have some knowledge of the various types of structures that occur, and of their naming and classification. For example, what is meant by the words "phenyl," "ethyl," and "alcohol," and how do these relate to the odor and other characteristics of the material known as "phenylethyl alcohol" ... 

The four main factors that affect the volume of use of a fragrance ingredient are its odour contribution to a fragrance, its stability and performance in the products to be perfumed, its safety in use and its cost. The first three factors are discussed in the chapters on perfumery, applications, safety and ingredient design (Chapters 7, 9, 10 and 15, respectively). The fourth factor, cost, depends on raw material availability and chemical process technology, which are discussed in this chapter. 

---