A Ionone

Citral reacts in an aldol condensation using excess acetone and a basic catalyst, usually sodium hydroxide. The excess acetone can be recovered for recycle. The resulting intermediate pseudoionone [141-10-6] (83) after cyclization with phosphoric acid gives predominantly a-ionone [127-41 -3] (84), which is the isomer commercially important in flavors and fragrances. A hydrocarbon solvent is generally necessary in order to get high yields. P-Ionone [14901-07-6] (85) is the predominant isomer if sulfuric acid is used as the catalyst but lower temperature than that for cyclization to a-ionone is required. y-Ionone [79-6-5] (86) is also produced. 

The production of a- and P-ionone ia the United States ia 1993 was about 120 t at an average price of 26.48/kg (67). a-Ionone is more valuable than P-ionone ia perfumery and sells for an average price of 30.41 /kg. P-Ionone is produced ia large volumes and production figures are not available. It is used mainly as an iatermediate for produciag Vitamin A. Production figures for methylionones are not available but they are much larger than the a- and P-ionones used for perfumery. 

This body is. now recognised to be a mixture of two isomeric ketones, known as a-ionone and j8-ionone. The commercial article, which is a mixture of the two ketones has approximately the following characters —... 

In conjunction with Bachofen, Chuit has devised a method for separating the isomeric ionones depending on the following facts. The method is based on the insolubility of the sodium salt of the hydrosul-phonic compound of a-ionone in the presence of sodium chloride, whilst the corresponding j8-compound remains in solution. If sodium chloride be added to a hot solution of the hydrosulphonic compounds, separation of the n-salt takes place slowly as the solution cools, and the salt crystallises in fine white scales, which can be recrystallised from hot water. The j8-compound remains in solution. 

The composition of the ordinary hydrosulphonic sodium compound of a-ionone is, according to Chuit,... 

From the point of view of practical perfumery, Chuit points out that the possession of the two pure isomers enables perfumers to produce numerous shades of violet perfume, with characteristic and distinct odours, a-ionone has a sweeter and more penetrating odour, rather resembling orris than violets, whilst 8-ionone is said to more closely resemble the true fresh violet flower. 

Lutz-Wahl S, P Fischer, C Schmidt-Dannert, W Wohlleben, B Hauer, RD Schmid (1998) Stereo- and regio-selective hydroxylation of a-ionone by Streptomyces strains. Appl Environ Microbiol 64 3878-3881. 

Fig. 6.32. El mass spectra of a- (a) and P-ionone (b). RDA reaction proceeds via loss of isobutene, causing the m/z 136 peak in case of a-ionone, whereas ethene loss is almost absent in the P-ionone spectrum. Spectra used by permission of NIST. NIST 2002.

Marshall, D. A. and Moulton, D. G. (1981). Olfactory sensitivity to a-ionone in humans and dogs. Chemical Senses 6,53-61. 

Both optical isomers of a-ionone are found in nature. Generally, ionones have a trans configuration, trans-a-lonone can be converted into the cis isomer by exposure to ultraviolet light. Under the same conditions, trans-(3- onone rearranges to the retro compound. 

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