Читать книгу Aromatherapy Workbook - Shirley Price - Страница 46

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.