Rhodinol

The last of these bodies announced as being alcoholic constituents of rose and geranium oils was reuniol, found in various geranium oils (BAunion, African, and Spanish) by A. Hesse. This had previously been announced as a probable chemical individual by Barbier, but he stated that he had not obtained it pure. Erdmann and Huth claimed that it was more or less pure rhodinol. 

Up till about three years ago, there appeared to be little reason to doubt that rhodinol was in fact an impure form of citronellol, the reduction product of citroneUal being dextro-citronellol, whilst the natural alcohol, which the French chemists had termed rhodinol was considered to be laevo-citronellol. 

There seems, however, to-day, to be overwhelming evidence that the French chemists were correct and that citronellol and rhodinol are two very similar, but chemically different, compounds, citronellol being represented by the formula (1) and rhodinol by formula (2). Considerable evidence of this is to be found in the work of Barbier and Locquin. Starting from the acetic esters of ordinary d-citronellol and rhodinol from oil of geranium or rose, they attached hydrogen chloride to the double bond, and obtained the same additive product according to the equations — ... 

The authors found that on elimination of the halogen acid from this compound, rhodinol, and not citronellol, is regenerated, dextro-rhodinol from dextro-citroneUol, and laevo-rhodinol from the laevo-rotatory alcohol from oil of rosesior geranium, the two bodies, in the latter case being identical. 

This ester loses hydrogen chloride by the action of sodium acetate giving ethyl rhodinate which when reduced by sodium and absolute alcohol yields rhodinol. 

Citronellal can thus be converted into rhodinol without being first reduced to citronellol. 

A third method of converting citronellol into rhodinol is by hydrating citronellol by means of 30 per cent, sulphuric acid. This yields the glycol 3-7-dimethyl octanediol-1-7, of the formula—... 

I The three optical varieties of rhodinol have thus been obtained, namely, laevo-rhodinol, the natural constituent of rose and geranium oils dextro-rhodinol by conversion of dextro-citroneUol obtained by reduction of citronellal, and inactive rhodinol by the reduction of synthetic ethyl rhodinate. 

Further evidence of the difference between rhodinol and citronellol is forthcoming, in that the former yields on oxidation an aldehyde, rhodinal, whose oxime does not yield citronellic acid nitrile when treated with acetic anhydride, nor citronellic acid when the nitrile is treated with alkalis, wheras citronellal, the aldehyde of citronellol, does yield the nitrile and citronellic acid. 

Harries and Comberg have also supplied much evidence, which, taken with the above-mentioned researches, places the chemical isomerism of citronellol and rhodinol practically beyond dispute. By ozonisation experiments decomposition products were obtained, which proved that natural citronellal, obtained from citronella oil, is a mixture of about... 

The physical characters, therefore, of the bodies which have hitherto been described as citronellol or rhodinol must therefore be understood to apply to the respective bodies in as pure a state as their separation has rendered possible. At all events, it is clear that the two alcohols are very similar in their general characters. These characters s.re approximately as follows —... 

Citronellol and rhodinol have faint but sweet rose odours. 

This alcohol, Ci(,H2oO, is, like bupleurol, isomeric with citronellol and rhodinol. It is present in the oil of water fennel Phellandrmni aqiiaticum),. and has an odour characteristic of the plant. It has the following characters —... 

No aldehyde or ketone has been obtained from it by oxidation. Its constitution is probably allied to those of citronellol and rhodinol, but, since it contains an asymmetric carbon atom, as shown by its optical activity, the three formulae given under bupleurol obviously cannot represent androl. 

These aldehydes, of the formula Cj E gO, are those corresponding to the alcohols citronellol and rhodinol (assuming, as is apparently true, that they are distinct compounds as indicated under citronellol. Their constitutions would therefore be as follows —... 

The odor quality and strength of the two citronellol enantiomers were found to be different.The (35)(—)-enantiomer (Rhodinol) possesses a much finer rose odor than the (3i )(+)-enantiomer. (35)(-)-Citronellol has a sweat, peach-like flavor, while (3i )(- -)-citronellol has a bitter taste. (35 )(—)-Citronellol has been found in a number of geranium and rose oils. (3i )(+)-Citronellol occurs in the oils of Ceylon and Java citronella, Cymhopogon winttrianusff Boronia citriodora. Eucalyptus citriodoraff geranium, Spanish verbena and others. Because of the... 

Citronellol isolated from natural sources is often named rhodinol. At present, the name rhodinol is also used for the isopropenyl isomer, a-citronellol therefore, exclusive use of the systematic name is better. 

Alcohols, such as linalool (licareol, coriandrol), geraniol (lemonol, rhodinol, r6uniol), citronellol (the rhodinol or rduniol of some authors), tcrpineol, bomeol and menthol. The alcohols occur in these oils both in the free state and also in combination with acids as esters (see later). 

While it is true that materials of identical chemical structure have the same odor qualities and are indistinguishable in their effect upon the skin irrespective of their origin, it is also true that very often synthetic and natural perfume materials that have the same name are not really identical in the chemical sense. Rhodinol from geranium oil consists of a different mixture of optical isomers than synthetic rhodinol. Eugenol from clove leaf oil is accompanied by different impurities than synthetic eugenol. Hence the natural and synthetic materials do differ in their odor quality, and they may differ in their effects upon the skin. 

Rhodinol [see Citronellol, Geraniol, and Nerol colorless liq/ s—most fixed oils, 1 mL in 1.2... 

SYNS a-CITRONELLOL 3,7-DIMETHYL-7-OCTEN-1-OL FEMA No. 2981 RHODINOL (FCQ... 

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