PERFUMES IN PRESSURIZED PRODUCTS 231 PERFUMES IN PRESSURIZED PRODUCTS j. PICKTHALL, F.R.I.C.* A paper delivered before the Society at the Symposium on Pressurized Packs, on 14th October 1958. The essential requirements of a perfume are discussed, together with the manner in which a perfume may be affected by different types of pressure packs. OUR TRaDITIONaL handkerchief perfume is simply an alcoholic solution of a number of odorous ingredients. Its pressure-packed equivalent exists as an alcoholic solution of odorous ingredients, together with a liquefied propellant, usually of the halogenated hydrocarbon type. To understand just how the different type of presentation (conventional or pressurized) might affect the odour and stability of a perfume, it is neces- sary to discuss the essential nature of a perfume. Blending Despite many recent papers on the subject, we are not much nearer to solving the mystery of olfaction. To a limited extent, a perfumery chemist can anticipate the odour which a pure chemical will possess. The odour which will result from a mixture of known chemicals is less easy to forecast. If two chemicals of identical vapour pressure are mixed and exposed to the atmosphere, one can in some cases perceive the two odours quite distinctly in other cases one is conscious of a new odour in which neither of the original constituents can be identified. In the first case, one is dealing with chemicals which possess little or no attraction for each other so that each retains its own particular type of odour. In the second case, one is undoubtedly dealing with complex formation due to the physical attraction between the different types of molecules. These forces of attraction will include hydrogen bonding, dipole attraction and van den Waals. In a perfume the concern is with mixtures which contain many separate chemicals, whether of natural origin or synthetically produced, and obviously this question of molecular attraction becomes extremely complicated the poor perfume remaining just a mixture and the good perfume achieving success as a "blend". The ultimate aim in perfumery is to blend together a number of odorous materials and to replace the individual odours by one pleasant impression. * Polak & Schwarz (England), Ltd., Enfield, Middlesex.

232 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS This aim is never reached, success coming only in degrees. Blending, as described above, occurs immediately the ingredients are homogeneously mixed. As the molecules leave the surface of the blend, so they become separated and blending effects diminish. Conditions of dispensation greatly affect the odour of the perfume as the nose receives it, concentration, surface and humidity all playing an important part. Ageing As is well known, the odour of a perfume changes with age. Regrettably, the changes are not always for the best, but this is due to faulty formulation. Blending is due to physical effects and occurs immediately the mixture is completed: ageing is the result of chemical changes and proceeds to equili- brium with time. With mixtures of alcohols, acids, esters, aldehydes, acetals, ketones, ethers, phenols, amines and terpenes, chemical action and inter- action will take place with resultant changes in odour. Ester formation, ester exchange, acetal or hemi-acetal formations, Schiff base formation, aldol condensation and a host of other reactions can be anticipated. In addition, chemical breakdown and oxidation must be considered. l•'ixation Fixation of a perfume is achieved by the selection of high-boiling sub- stances which have powers of attraction for the more volatile ingredients. The very blending of ingredients is in fact a form of fixation. To return to the main subject, namely, pressurized packs, let us consider typical spray perfumes to be packed in glass containers, adequately protected by a plastic coating. The type of spray employed will depend upon the use to which the product will eventually be put. Three important types are: Wet spray for the genuine Eau de Cologne. Semi-wet spray for the sophisticated toilet water. Dry spray for the true handkerchief perfume. The above spray characteristics are determined by the composition of the propellant, by the ratio of alcohol to propellant, by the water content and, finally, by the type of valve employed. A typical formula for a perfume spray is: Alcohol 90 per cent 60 Dichlorotetrafluoroethane 35 Dichlorodifluoromethane 5 Straight colognes may have between 3 and 5 per cent perfume, sophisti- cated colognes 4 to 8 per cent, and handkerchief perfumes between 8 and 15 per cent. This refers to the alcohohc solution, propellant absent. It xvill be noticed that these suggested amounts of perfume are higher than the