The Chemistry of Cloves

Cloves are a spice that you may well have stowed away somewhere in the kitchen; originally from the Maluku Islands in Indonesia, the spice itself comes from the flower buds of the clove tree. It is used to flavour food, imparting a sweet, aromatic flavour, and also one of the common spices used in the making of mulled wine. As well as this, the oil of cloves is commonly recommended as a traditional remedy for relieving toothache, amongst other conditions. So, what are the chemicals that make this use possible?

To start with, let’s consider the composition of clove oil. There are actually three types, depending on whether the oil is extracted from the buds, the leaves, or the stems of the clove tree; here, we’ll focus mainly on the bud oil. This is composed of three main compounds, as well as a myriad of minor constituents: eugenol, which accounts for around 70-85%, eugenyl acetate, which accounts for around 15%, and ß-caryophyllene, which accounts for 5-10%.

Eugenol is the major compound that allows clove oil to be used as a remedy for toothache. It has an impressively wide variety of properties: it’s an anaesthetic and antiseptic, and has anti-inflammatory, antifungal, antibacterial and insecticidal properties – quite the catalogue. In terms of toothache, we’re mainly concerned with the anaesthetic properties. These come about due to eugenol’s ability to affect nerves in areas to which the clove oil is applied. It inhibits the movement of sodium ions, lessening the nerves’ ability to communicate with the brain and transmit the sensation of pain.

Despite this, the FDA (US Food & Drug Administration) has stated that there isn’t currently enough evidence to rate eugenol as effective for the treatment of toothache. This isn’t to say it has no effect, and there are studies that have shown that it performs more effectively against toothache than a placebo, but that this effect has not been shown to be significant enough to be of major use.

Another odd use for cloves I came across during the research for this graphic was in a topical cream, in combination with some other ingredients, targeted at preventing premature ejaculation. Presumably this must also have something to do with eugenol’s effect on nerves. Slightly concerned about the spam emails & in-browser advertising I’m going to be getting after researching this effect…

Finally, the aroma of cloves is influenced by the presence of eugenol, but also by the presence of some minor compounds in the composition. One of these is methyl salicylate, an ester commonly referred to as oil of wintergreen; another is 2-heptanone, which has a fruity, spicy odour. 2-heptanone is particularly interesting; much like eugenol, it can act as an anaesthetic, and research has shown that it is also contained in the mandibles of honeybees. The compound is secreted when the honeybee bites intruders in its hive, paralysing the intruder and allowing it to be removed by the bee. This is a comparatively recent discovery, and the compound has been patented for potential use as an anaesthetic in humans in the future.

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References & Further Reading