38 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS SOME ASPECTS OF PERFUMERY CHEMICALS A Lecture delivered to the Society on the 8th December, 1955. A. J. KRAJKEMAN, Dipl. Ing. Chem., A.R.I.C.* The di•erent kinds of impurities which occur in aromatics are discussed. The Chemist and the Per•umer have a different approach to the problem of purity of aromatics. [luestions connected with this difference of approach are discussed and an attempt is made to explain it. IT w^s indeed an honour to me when I was invited by our secretary to give a lecture during this session of the Society. However, it was not only an honour, but also quite a shock. What on earth was I going to talk about ? Some aspects of perfumery chemicals, all right. But which aspects of perfumery chemicals have not already been dealt with at length by people who are much better qualified than I am to say something interesting on this subject ? It is not easy to discuss chemicals without doing one of three things. One can read an original paper. Now this is out of the question in my case because my activity is confined to production. Then one could, of course, discuss production, but again this is not possible without touching certain points which are considered vital secrets, although they are, in fact, more or less open secrets, as those with a knowledge of the industry are well aware. Finally, one can dwell on generalities, but this has the danger of being utterly boring. Nevertheless, in spite of this danger, I have decided to discuss one general point one which is constantly in the minds of those who produce perfumery chemicals, namely, the degree of purity of aromatics. There are two different approaches to this question of purity of aromatics: the approach of the manufacturer who is an organic chemist, and the approach of the consumer who is a perfumer. That these two have quite a different approach can be well illustrated by an everyday occurrence. A chemical has been manufactured, perhaps three or four stages are involved in the process--chemically highly complicated stages. The chemist has done all he can to produce a satisfactory product. The yield is good, the analytical figures show that a pure product has been prepared, and a sample is proudly presented to the perfumer. The perfumer smells it and says in cold blood-- "it stinks." He does not care if this verdict of his means to the chemist another series of chemical reactions which may, and in fact in most cases does, upset production schedules. And he is quite right, too. He wants his per- fume ingredient to possess just the right note, as otherwise it will spoil his final composition. So it is left to the chemist to think of a method for further purification of the product, and when he has finally succeeded and the * S6flor Ltd., Wadsworth Rd., Perivale, Middlesex.

SOME ASPECTS OF PERFUMERY CHEMICALS perfumer has graciously approved of the odour, it is found that the price of the product is too high. Now impurities which influence the odour of an aromatic can be roughly classified into three categories: Firstly, traces of starting materials. Secondly, by-products and isomers produced as a result of side reactions during manufacture, and Thirdly, traces of decomposition products formed in the final material on storage. We are concerned here, of course, with proportions of impurities which hardly influence the physical constants of the products in which they occur, but appreciably change their odour. As an example of the first category, traces of starting materials, we may mention anisaldehyde or aubepine ex p-cresol. It is well known that the slight phenolic note due to traces of p-cresol is difficult to remove. Another example in this category is that of some esters, in the manufacture of which certain amines are used as catalysts, and it is quite often difficult to remove the last traces of such amines. The only means of producing materials with satisfactory odours in such cases is to use different starting materials. For example, anethole may be used instead of p-cresol for the production of anisaldehyde, and in the case of esters different catalysts have to be employed. As an example of the second category of impurities, the by-products and isomers produced as a result of side reactions, we may mention terpineol manufactured irom terpin hydrate. Four isomers are obtained in this process: alpha-terpineol, beta-terpineol, gamma-terpineol and terpinenol. The com- mercial grade is a mixture of alpha and beta terpineol, and a camphory note of certain qualities is due to the presence of traces of the other two isomers. Then there is the case of linalyl acetate. As you know, under certain conditions linalool is converted to terpineol by the action ot acetic anhydride. If such conditions are given during the manufacturing process of linalyl acetate, the traces of terpineol so formed are acetylated to terpinyl acetate which then causes that objectionable resinous note which is sometimes found in linalyl acetate. Once present, it is very difficult, if not almost impossible, to remove these traces of terpinyl acetate. The last category of impurities, you will remember, includes decomposi- tion products formed on storage. Here may be mentioned aldehydes which are oxydised to acids with pronounced odours. Also certain esters may be mentioned which hydrolyse on standing, such as butyrates which develop a note of butyric acid on storage. Now the chemist will always endeavour to produce chemicals in as pure a state as he possibly can. He is a scientist, his criterion is chemical analysis, and he has figures to guide him specific gravity, refractive index, percentage