SOME ASPECTS OF PERFUMERY CHEMICALS 41 A similar instance is that of peach aidehyde. The typical--shall we say-- "spicy note" of this aromatic is due to traces of dihydrojasmone produced as a by-product as a result of a side reaction. Peach aldehyde which has been so completely purified that the last traces of dihydrojasmone have been removed has a fatty, dull and uninteresting odour. In my opinion the coconut note in so-called coconut aidehyde is also produced by a trace of a by-product. When this is absent the lactone smells very similar to peach aldehyde from which the all-important trace of dihydrojasmone has been removed. Certain brands of coconut aldehyde have a peculiar plum-like note. This, too, is caused by a by-product, so that according to the method of working up or purification of the crude reaction mixture it is possible to obtain either a coconut-like, or a plum-like, or even an indifferent smelling aromatic. In the production of ionone the two isomers alpha and beta ionone are obtained. Both are used individually in perfumery, but their mixture, known in the trade as "Ionone 100 per cent," is an even more valuable aromatic. Alpha ionone is always predominant in this mixture, but the proportion of beta ionone depends entirely on the manufacturing process used for the preparation of the final product. This is the reason why 100 per cent ionones from different sources may have different odour characters. In some reactions even more than two isomers are formed. For example, four products are obtained in the manufacture of methyl ionone: alpha and beta methyl ionone and alpha and beta iso methyl ionone. The proportion in which these isomers are found in the final product will determine its final odour quality. Now let us turn to the last category, the chemicals which contain decom- position products formed during storage. The example which springs to mind here is alpha amylcinnarnic aidehyde. This aldehyde undergoes oxida- tion on standing, and the decomposition products are benzaldehyde and certain fatty acids. On one occasion I prepared a highly purified sample of amylcinnamic aldehyde which was stabilised to prevent oxidation. To me it smelled like pure jasmin. But when the sample was submitted to a highly competent perfumer his verdict was that it lacked in body. He was missing the familiar fatty almond note which is always present in amylcinnamic aldehyde together with the jasmin note. In his opinion I had produced a very nice product which, however, he considered to be a new aromatic and which he could not introduce into his compounds in place of the amylcinna- mic aldehyde he was used to. Why then does the perfumer use aromatics which are known to contain impurities and uses them because of the odour produced by the impurities ? In my opinion this is due to the fact that when these products were first introduced into perfumery they were not known to be impure. Most syn- thetics were introduced at a time when the technique of synthetic methods

42 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and organic analysis were still in their infancy. The chemistry of the products was not known sufficiently and so they were accepted for what they were: valuable perfumery ingredients. To-day, with modern methods of synthesis and analysis, we can produce these well-studied products free from impurities, but we must realise that by doing so we are in many cases introducing entirely new aromatics which cannot indiscriminately replace the older, impure versions. When a new chemical is made for the first time and is found to have outstanding qualities as a perfumery chemical it may be accepted by the perfumer long before its chemistry is sufficiently known. The original method used for its preparation may not be economical, because in developing a new perfumery chemical the chemist will concentrate in the first place on prepar- ing the chemical by hook or by crook rather than on obtaining it in a good yield. But when the demand for this aromatic is created he will have to try to find the most economical process for its preparation. Then it may well happen that he will finally devise a process which, although producing the desired compound in a good yield, will not produce at the same time a by- product formed in the original reaction used for the preparation of this aromatic in the first place. If the odour character of the aromatic in question was determined by this by-product formed in thi• original reaction, but not obtained in the more economical process, then the odour quality of the aromatic prepared by the latter will be different from that made by the first method. In view of what has been said so far one may well ask which aromatics should be produced in as pure a state as possible, and which of them should be left to contain certain impurities. As a rough guide one could say that most isolates should be as pure as one can make them. There will surely be no difference of opinion on samples of pure citral, pure citronellal, pure geraniol, pure eugenol, to name only a few isolates. Not so with synthetics. Of course, a large number of synthetics will not be acceptable unless they are free from impurities. Such products are probably those the chemistry of which was well known at the time when they were introduced into perfumery, and which consequently were intro- duced into perfumery in the pure state. Most esters can be named here fatty aldehydes, coumarin, beliotropin, to name only a few more. But the evaluation of other synthetics is, in many cases, a matter of personal preference. I have quoted the example of amylcinnamic aidehyde, and have already mentioned the different types of peach aldehyde and coconut aldehyde as well as the ionones and methyl ionones containing vary- ing proportions of the different isomers. As an additional example take the case of vanillin. Until not so many years ago vanillin was only acceptable when it had a faint yellow colour in