SOME ASPECTS OF PERFUMERY CHEMICALS 43 fact, it was generally accepted that pure vanillin was a faintly yellow product. Later, the intricate chemistry of phenolic aldehydes became better known, and with this knowledge, and with the help of modem techniques and plant made from entirely new materials of construction, the manu- facturers were in the position of preparing vanillin in its pure, white form. But it took quite a number of years before flavour chemists and perfumers became used to white vanillin and realised that its odour was not inferior, but at least equal to, if not better than, that of the yellow material. Well then, the question which aromatics should be prepared in a pure state and which should be left to contain certain impurities can only be answered as follows: . . . purify as far as possible those products which the perfumer requires in the highest degree of purity do not attempt to separate reaction mixtures which are valued by the perfumer on account of the very fact that they are mixtures. But in actual fact the answer is not as simple as that: remember per- fumers are artists and, as I have said, the evaluation of certain products is a matter of personal preference. What one perfumer regards as a good quality aromatic because of the absence of any foreign note, another perfumer may regard as poor because of this very absence. What one perfumer regards as good ionone because of an excess of beta ionone, another may regard as poor because of this excess. This makes the industry of aromatics so different from the industry of other types of fine chemicals. Take, for example, pharmaceutical chemicals. The purer they are the higher they are valued, and their quality is determined by analysis alone. Not so in the industry of aromatics. It frequently happens that one customer will be delighted to have a certain quality of a certain product, and another customer will threaten to break off diplomatic relations if such a poor quality product is supplied to him again. What, then, is the manufacturer to do in order to satisfy all his customers?' The answer is that he has to offer more than one quality of one given aromatic. This has, of course, quite another aspect, too, which I have not mentioned so far, namely, the economic aspect. As you are well aware, there are many methods available for the purifica- tion of chemicals. A liquid product may be converted to a solid derivative which is repeatedly purified by crystallisation to remove all foreign materials. The liquid product is regenerated from the solid derivative, fractionated in vacuum, and possibly redistilled. A solid product may have to be crystallised from a number of solvents. Liquid-liquid extraction and a variety of other methods could be enumerated. But all these methods are costly, so that the further a product ha•, to be purified, the more expensive it becomes. I did say that the perfumer does not always consider the chemically pure material to be the most suitable for his purpose. And so quite often it is.

44 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS found that a cheaper grade of a given aromatic will appeal to the perfumer much more than the highly refined expensive grade. A hard-and-fast rule cannot be laid down, but one can safely say that a low price is not always an indication of a poor product, and a high price does not always mean an aromatic which is most suitable for your purpose. Let me then briefly summarise. The perfumer requires certain aromatics in the chemically pure state. These are mainly isolates, but also certain synthetics. He requires other aromatics in an impure state, speaking from the point of view of the chemist. Furthermore, one perfumer insists on a large proportion of impurity to be present, another perfumer demands the same aromatic with as little impurity as possible. But all perfumers agree on one aspect: to get the product they want for the lowest possible price. So the manufacturer, as I have already said, has to offer different grades of one given aromatic, different in odour quality and in price. But the number of grades he can afford to offer is naturally limited, and so he, too, has to come to the well-known conclusion that it is impossible to satisfy everybody, the reason in this particular case being the element of personal preference, both olfactory and economical preference, that is always present in the evaluation of certain aromatics. So, after having decided on the number of grades of a given aromatic and on the physical and chemical specifications with which they will have to comply, the manufacturer must adopt this principle: to produce his different grades of aromatics in a consistent olfactory quality. Only then will the perfumer be able to rely on a supply of perfumery chemicals which have a degree of purity that meets his requirements. DISCUSSION Mr. Pickthalt: Referring to the speaker's comments on trichlor phenyl methyl carbinyl acetate, I think it is well known that the typical rose odour develops on standing. Nevertheless, I believe that even the most highly purified laboratory sample still retains a definite odour. Author: In my opinion this may be a matter of personal judgement. It is a fact, however, that when the ester is crystallised the odoriferous "impurity" goes into the mother liquor and can be isolated. I have prepared an "odourless" sample of the ester. Mr. Pickthalt: On the subject of a perfumer's idiosyncrasy on impurities in a raw material, I should have thought the manufacturer would have had less trouble in producing relatively pure synthetics than would be the case with isolates. With the latter one is forced to use nature's starting material, and separation of the constituents by distillation is often extremely difficult. In synthetics the manufacturer can use his ingenuity to produce a chemical which, within the meaning of the word, is "pure."