Terpene aldehydes, functional groups

Spices impart aroma, colour and taste to food preparations and sometimes mask undesirable odours. Volatile oils give the aroma, and oleoresins impart the taste. Aroma compounds play a significant role in the production of flavourants, which are used in the food industry to flavour, improve and increase the appeal of their products. They are classified by functional groups, e.g. alcohols, aldehydes, amines, esters, ethers, ketones, terpenes, thiols and other miscellaneous compounds. In spices, the volatile oils constitute these components (Zachariah, 1995 Menon, 2000). 

Terpenoids Components of essential oils based on the hydrocarbon skeleton of terpene plus a functional group such as an aldehyde, alcohol or ketone. 

Many terpenes contain additional functional groups, especially carboxyl groups and hydroxyl groups. A terpene aldehyde, a terpene alcohol, a terpene ketone, and a ter-pene acid are shown next. 

Citral is an example of a very large group of natural products called terpenes. They are responsible for the characteristic odors of plants such as eucalyptus, pine, mint, peppermint, and lemon. The odors of camphor, menthol, lavender, rose, and hundreds of other fragrances are due to terpenes, which have ten carbon atoms with double bonds, and aldehyde, ketone, or alcohol functional groups. (See Fig. 2.)... 

The most widely occurring terpenes are the smallest molecules, that is, the monoterpenes, CioHjg, and their oxygenated derivatives such as ketones, aldehydes, alcohols, oxides, phenols, along with simple hydrocarbons. Their properties are determined by functional groups—oxygen-containing radicals attached to the carbon skeleton. 

Ketones are closely related to aldehydes. Consideration of the polarity of the functional group leads us to expect that their 1 /-values will lie in the same region as those of the aldehydes and consequently corresponding to the terpene esters (cf. Table 24). This is apparent from the published data of Nigam and co-workers [183], Severin [237a] and Schratz and Qedan [228]. 

PCC not only is selective for the oxidation of primary alcohols to aldehydes but also has little effect on carbon-carbon double bonds or other easily oxidized functional groups. In the following example, geraniol, a primary terpene alcohol, is oxidized to geranial without affecting either carbon-carbon double bond. 

Apart from certain carbohydrates, the most inexpensive source of chiral compounds is the terpenes. These are readily obtained from plant sources and encompass examples of many important functional groups These include alcohols such as (+)-menthol (22) and (-)-bomeol (23), ketones such as (+)-camphor (24), (+)-pulegone (25), (-)-menthone (26) and (-)-carvone (27), the aldehyde (+)-citronellal (28), (+)-camphor-10-sulphonic acid (29), and alkenes such as (+)-limonene (30) and (+)-a-pinene (31). (a)-Pinene provides a good illustration of the fact that naturally derived chiral compounds are not necessarily enantiomerically pure. Both enantiomers are readily available but the normal samples are only of around 90% e.e. Fortunately this is not a serious problem since procedures have been... 

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