Aldehydes citral

Doebner showed that certain aldehydes, citral, for example, form condensation products with pyruvic acid and )8-naphthylamine, known as naphthocinchoninic acids. The reaction takes place as follows —... 

Methyl-heptenone, CgH, 0, occurs in various essential oils, especially lemon-grass oil, in which it is associated with, and difi cult to separate from, the aldehyde citral. 

Among the acyclic terpene aldehydes, citral and citronellal hold key positions as fragrance and flavor chemicals, as well as starting materials for the synthesis of other terpenoids. Hydroxydihydrocitronellal is one of the most important fragrance materials. Derivatives of these aldehydes, particularly the lower acetals, are also used as fragrance materials. Acyclic sesquiterpene aldehydes are not very important as such, but they contribute to the characteristic fragrance and aroma of essential oils, for example, in the case of a- and /3-sinensal in sweet orange oil. 

The aldehyde citral displayed moderate activity [49-52]. Ketones such as pu-legone [53-56], fenchone [39, 57], a-thujone [58] and camphor [48-67] were reported to have antimicrobial activities. 

Many aldehydes are particularly fragrant. A number of flowers, for example, owe their pleasant odor to the presence of simple aldehydes. The smells of lemons, cinnamon, and almonds are due to the aldehydes citral, cinnamalde-hyde, and benzaldehyde, respectively. The structures of these three aldehydes are shown in Figure 12.21. The aldehyde vanillin, introduced at the beginning of this chapter, is the key flavoring molecule derived from the vanilla orchid. You may have noticed that vanilla seed pods and vanilla extract are fairly expensive. Imitation vanilla flavoring is less expensive because it is merely a solution of the compound vanillin, which is economically synthesized from the waste chemicals of the wood pulp industry. Imitation vanilla does not taste the same as natural vanilla extract, however, because in addition to vanillin many other flavorful molecules contribute to the complex taste of natural vanilla. Many books made in the days before acid-free paper smell of vanilla because of the vanillin formed and released as the paper ages, a process that is accelerated by the acids the paper contains. 

The isolated aldehyde citral can be a skin irritant or sensitizer and has been implicated in reproductive disorders. In Citrus Union (lemon oil) it makes up to 5% of the composition. It has been shown that the hazardous effects are markedly reduced by the presence of the terpenes d-limonene and a-pinene also present in the oil. 

Hall, M., Hauer, B., Stuermer, R., Kroutil, W., and Faber, K. 2006. Asymmetric whole-cell bioreduction of an oc,P-unsaturated aldehyde (citral) competing prim-alcohol dehydrogenase and C-C lyase activities. Tetrahedron Asymm., 17, 3058-3062. 

Examples of monoterpenes include the linear aldehyde citral, which is found in many essential oils, and the (cis) alcohol geraniol, a major component of oil of geranium. Cyclic monoterpenes include limonene, menthol, pinene, camphor, and carvone, major components of lemon oil, mint oil, turpentine, camphor oil, and caraway oil, respectively. Sesquiterpenes include farnesol, a component of rose oil, and bisabolene, a component of Bisabol myrrh. The diterpenes include phytol, a component of chlorophyll, and vita-... 

The flavour properties of the citrus oils are based on compounds like aldehydes, esters and alcohols. Aldehydes play the most important role in citrus flavours. Mainly the saturated C-8, C-10 and C-12 long-chain constituents as well as the terpenoid aldehydes citral (a mixture of neral and geranial) and citronellal form the basic notes of the fresh and pleasant citms flavour. Also sesquiterpene aldehydes and ketones, such as sinensal or nootkatone, are significant for citms flavours. The aldehyde content, therefore, is frequently used as a quality criterion for citms oils. Important citms alcohols are linalool, octanol, a-terpineol (especially in distilled lime oil) and ter-pinen-4-ol. Furthermore, esters contribute to the flavour properties of citms oils. Especially the acetates of geraniol and nerol and, to a lesser extent, citronellol are... 

For example, various ionic liquids (ILs), together with Pd-metal species, were immobilized on a high-surface area, of an active carbon support. The resulting SILCA catalysts were studied in the production of fine chemicals, and in particular in the hydrogenation of unsaturated aldehydes, citral and cinnamaldehyde (Figure 4.8). 

In another example, nanodustered Pt(0) catalysts based on cross-linked macro-molecular matrixes were evaluated in the hydrogenation of an a,(i-unsaturated aldehyde, citral. The monometallic catalysts exhibit remarkable selectivity for gera-niol/nerol when 2-3 nm, regularly shaped, spherical metal nanoclusters are deposited on the supports from solutions of solvated platinum atoms prepared by metal vapor synthesis (MVS). The immobilization in the polymer framework of ions of a second metal such as Fe(II), Co(II), or Zn(II) enhances the selectivity of the Pt catalysts by up to more than 90% [18],... 

The jS-cyclocitrylidene acetaldehyde synthesized in this way was recovered for the first time in crystalline form. The two aldehydes, citral and 0-ionylidene acetaldehyde, are of special value because they are intermediate products in the synthesis of Vitamin A and other caiotinoids. 

Citrus oil components were evaluated for attractive or repellent activity toward the red scale, Aonidiella aurantii. Most hydrocarbon terpenes were attractive, while the alcohols, including linalool, were repellent. One aldehyde, citral, was attractive, while the other, citronellal, was repellent (21). 

Quenching is a process used in the perfume industry to suppress contact sensitisation from cinnamic aldehyde, citral, and phenylacetaldehyde by the addition of another agent, usually an alcohol or terpene (Opdyke 1976). More recent studies, however, have not been able to confirm the initial promising findings (Basket-ter and Allenby 1991). 

IFRA and RIFM have forbidden the use of several essential oils and components, including costus root oil, dihydrocoumarin, musk ambrette, and balsam of Peru (Ford, 1991) a concentration limit is imposed on the use of isoeugenol, cold pressed lemon oil, bergamot oil, angelica root oil, cassia oU, cinnamic alcohol, hydroj citronellal, and oakmoss absolute. Cinnamic aldehyde, citral, and carvone oxide can only be used with a quenching agent. 

Lemon oil, prepared by expressing the peel of the nearly ripe fruit of Citrus limonum, and obtained almost entirely from Sicily and Southern Italy. Specific gravity at 15° C., 0 856-0 860 optical rotation, + 58° to + 63° refractive index at 20° C., 1 4730-1 4750 aldehydes (citral), 2 5 to 4 per cent. 

The aliphatic unsaturated aldehyde citral is one of the most frequently occurring compounds. Natural citral is always a mixture of geranial (8-40), also known as (E)-citral or citral a, and neral (8-40), which is known as (Z)-citral or citral b. The precursor of geranial and neral is geraniol. Citral occurs in the aheadymentioned citroneUa oU in concentrations of 11-13%. In the oU of the Litsea cubeba (Lauraceae) tree, native to Southeast Asia, citral is found in concentrations up to 75%. In much smaUer amounts, citral is... 

It contains cinnamic aldehyde, citral cineol, and linalol. Oil from the trunk wood contains cinnamic aldehyde and eugenol, and oil from the root bark contains cinnamic aldehyde, camphene, linalol, and cineol. Other cinnamon oils of less importance are as follows —... 

Lemon oil contains a considerable number of constituents, of which the principal is the aldehyde citral, which is present to the extent of from 4 to 5-5 per cent., rarely up to 6 per cent. Burgess and Page have isolated a hydrocarbon, which is interesting as being quite different frona the terpenes so generally found in the citrus oils. It has the following characters —... 

The so-called rose alcohols (geraniol, nerol, citronellol, and linalool) together with the corresponding aldehydes citral and citronellal, lie at the heart of the major production routes in terpenoid chemistry as shown in Fig. 8.7. In this figure, the basic feedstocks are contained in ellipses and it can be seen that there is a balance between natural (hence, renewable) and petrochemical feedstocks. 

Cinnamic aldehyde Citral Citronellal Cuminaldehyde Decylic aldehyde... 

Anisic aldehyde Benzaldehyde Benzyl acetate Benzyl alcohol, B.P. Benzyl benzoate, B.P. Bornyl acetate (wo) Bromstyrol Cinnamic aldehyde Citral Citronellal Citronellol Coumarin... 

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