FIGURE 3.17: a) menthone; b) acetone (ketones)
These are easy to identify as they always end in ‘one’. (N.B. A false friend is asarone, which is a phenolic ether in carrot oil.) A common one, not occurring in essential oils, but known to most people, is acetone (nail polish remover). Fortunately, ketones are not present in the majority of essential oils – I say ‘fortunately’ because many of them are not ‘user friendly’ and have to be employed with knowledge and care, as several are neurotoxic. There is no scientific proof that all ketones are hazardous and generally (and fortunately) those which are known to be very much so occur in oils not used by aromatherapists, e.g. tansy, buchu, thuja, rue, etc.
Oils used in aromatherapy which contain significant amounts of ketones are aniseed, caraway, hyssop, pennyroyal and sage, and in France, only pharmacists may sell hyssop and sage oils. It is thought that the ketone in hyssop (pinocamphone) may provoke an epileptic fit in someone predisposed to them and that a few ketones, e.g. thujone and pulegone, if used in overdose, may provoke a miscarriage.
At the EOTA conference (June 1990) at Brunel University, Dr K. Tyman said that ‘there are 4 different thujones and a change in molecular shape means a change in effect’. Dr Tyman made what I feel to be a most important statement, which explains why sage, supposedly very hazardous because of its high thujone content, does not in practice appear to be so.
He explained that because the thujone molecule can arrange itself in four different ways (alpha-thujone, beta-thujone, etc.) it is feasible to expect all four to have different pharmacological effects; therefore it may be that not all thujone molecule shapes will necessarily present a hazard.
Carvone, for example, present in caraway and dill oils (the latter is an ingredient in gripe water for babies), is assumed to have the hazards of all ketones, yet there is no evidence to prove this. In fact, it is believed that some ketones (like carvone) may be completely harmless. There are two forms of carvone, laevo-carvone and dextro-carvone, which may, as with the thujones, have different pharmacological effects. The properties of the two forms of carvone are different and they certainly have different aromas. Having said that, until further information comes to light we should take care with all oils containing ketones in any appreciable amount, just to be on the safe side – and it pays to know your chemistry!
Provided caution is exercised and oils containing ketones are well diluted (1–2 per cent maximum) and not used too often or for too long, their effects are calming and sedative, they break down mucus and fat and encourage the healing of wounds by the formation of scar tissue. Certain ketones are digestive, others are analgesic, stimulant or expectorant.
Acids and Esters
Organic acids are nothing like inorganic acids, which are potentially dangerous e.g. sulphuric acid.
Inorganic acid + alkali = inorganic salt + water
Organic acid + alcohol = ester + water Acids and esters are based on the carboxyl group (see Figure 3.20b).
Acids in their free state are quite rare in essential oils and occur only in minute quantities. See Figure 3.18. As they have no known hazards there is no need to go into greater detail than to say they are anti-inflammatory. I mention them mainly so that you can follow the molecular progress to an ester.
FIGURE 3.18: a) benzoic acid; b) phenylacetic acid (neroli); c) acetic acid (found in aromatic waters)
Acids are mostly found in essential oils in a combined state with esters, which we shall be looking at next.
There is no ester group as such (like the hydroxyl or carboxyl groups mentioned earlier) because an ester is the result of the reaction between an organic acid and an alcohol to give an ester plus water. See Figure 3.20a.
FIGURE 3.19
The reverse can also happen; an acid plus alcohol is the result of the reaction between an ester and water. This is why I said above that acids are found ‘in a combined state’ in essential oils – it is possible that an interchange can be going on all the time. Perhaps this may be why esters are good balancers.
FIGURE 3.20: Formation of an ester
The last part of an ester’s name is nearly always ‘ate’, making it another component easy to recognize (in some cases, the name ester is used).
Esters are gentle in action and are free from hazard except for methyl salicylate in wintergreen and birch oils (over 90 per cent), which are not recommended for use by aromatherapists. Esters generally are anti-inflammatory and are effective on skin rashes and other skin problems. They can both calm and uplift, combining the calming properties of ketones with the tonic virtues of alcohols, so they are very balancing, especially to the nervous system.
Oxides
These are rare in essential oils with the exception of 1,8-cineole, also known as eucalyptol. Some oxides have the name ‘oxide’ at the end, making recognition easier.
FIGURE 3.21: 1,8-cineole, an oxide
1,8-cineole (eucalyptol) – see Figure 3.21 – is found in a number of oils and its major effect is due to its mucolytic property, useful in coughs, colds and any congestion in the respiratory tract. It can be a skin irritant and in this respect any oil containing a two-figure percentage needs to be used with restraint.
This group tends to be confusing, and it seems uncertain whether some oxides are in fact phenols or phenolic ethers – even experts have differing opinions or are not sure themselves. To be safe, give them the same consideration and prudent use as recommended for the phenols. 1,8-cineole may also be described as a bicyclic ether.13
Lactones
Lactones are easy to remember because they occur mostly in expressed oils, being too large to come over in distillation. Jasmine absolute has been found to contain a lactone, but as you will remember, this oil is not an essential oil, as it is not obtained by distillation and therefore larger molecules can pass into the solvent used for the extraction process.
As the percentage of lactones present in any oil is extremely low, they may generally be regarded as non-toxic. They have been found to be more effective than ketones for lowering temperatures and relieving catarrh, and are the components responsible for skin photosensitization.
Lactones are widely distributed in nature; the most important members of this class (or chemical family) occurring in essential oils are the coumarins and coumarin derivatives.
Coumarins and Furocoumarins
Coumarins are generally found to be sedative and calming yet at the same time uplifting and refreshing. They are also noted for their anticoagulating properties, which makes them good hypotensives. See Figure 3.22.
FIGURE 3.22: Bergaptene, a coumarin
Furocoumarins,