Aldehydes, fragrant

Many esters occur naturally Those of low molecular weight are fairly volatile and many have pleasing odors Esters often form a significant fraction of the fragrant oil of fruits and flowers The aroma of oranges for example contains 30 different esters along with 10 carboxylic acids 34 alcohols 34 aldehydes and ketones and 36 hydrocarbons... 

Salicylic aldehyde is an almost colourless oil with a fragrant odour of meadowsweet. Its constitution is as follows —... 

Aldehydes occur naturally in essential oils and contribute to the flavors of fruits and the odors of plants. Benzaldehyde, C6H5CHO (8), contributes to the characteristic aroma of cherries and almonds. Cinnamaldehvde (9) is found in cinnamon, and vanilla extract contains vanillin (10), which is present in oil of vanilla. Ketones can also be fragrant. For example, carvone (Section 18.1) is the essential oil of spearmint. 

Trimethyl-9-undecenal is a richly fragrant substance that is used in flower compositions to obtain an aldehydic note. 

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. 

Ferul aldehyde Sassafras (Lauraceae), Ocimum, Oreganum (Lamiaceae), Myristica fragrant (Myristicaceae), Piper (Piperaceae), Rosa (Rosaceae) spp., Camellia sinensis (tea) (Theaceae) Widespread per reduction of TYR (77)... 

Citral, a fragrant terpene aldehyde made up of two isoprene units, is the main component of the steam-volatile fraction of lemon grass oil and is used in a commercial synthesis of vitamin A. 

The lower molar mass aldehydes have a sharp odor, though the odor becomes more fragrant as the molar mass increases. Thus, many aldehydes are used in perfumes and for food flavoring. 

When allylic alcohols are used as an alkene component in HR, elimination occurs from an oxygen-bearing carbon, and aldehydes or ketones are obtained, rather than jS-arylated allylic alcohols [68,69]. The reaction of methallyl alcohol (113) with a halobenzene is a good synthetic method for dihydro-2-methylcinnamaldehyde, an important fragrant compound 114. The allylic alcohol 115 is not formed. An intramolecular version of the aldehyde formation was applied to the preparation of the key intermediate 117 from 116 in the total synthesis of saponaceolide [70]. 

Several naturally occurring aldehydes and ketones have very fragrant odors and are used in flavorings (see I Figure 4.7 and I Table 4.3). 

Aldehydes and ketones are a large family of organic compounds that permeate our everyday lives. They are responsible for the fragrant odors of many fruits and fine perfumes. For example, cinnamaldehyde (an aldehyde) provides the smell we associate with cinnamon, and civetone (a ketone) is used to provide the musky odor of many perfumes. Formaldehyde is a component of many building materials we use to construct our houses. The ketones testosterone and estrone are known to many as hormones responsible for our sexual characteristics. And the chemistry of aldehydes and ketones plays a role in how we digest food and even in how we can see the words on this page (see A Word About... The Chemistry of Vision on pages 76-77). So what are aldehydes and ketones ... 

Many of the higher aldehydes and ketones have pleasant odors, and some of the aromatic aldehydes are used as flavors. An example is vanillin, the fragrant principle of the vanilla bean its structural formula is... 

Vanillin is seen to be a phenol and an aromatic ether as well as an aldehyde. An example of a strongly fragrant ketone is miiscone, which is... 

In this experiment we wHl isolate the principal component of the oil of cinnamon, another naturally occurring aldehyde, cinnamaldehyde.The oil is first extracted from the dried parts of the Cinnamomum plant by steam distillation. Although this aromatic aldehyde is a component of an essential oil, it is not formed from mevalonic acid and is not a terpene. Cinnamaldehyde is also not an acetogenin nor is it related to usnic add.The origin of this fragrant material is shikimic acid, which is part of the plant s primary metabolism. 

Also another /r-menthenic terpene, y-terpinene, was screened as a substrate to afford a mixture of characteristically smelling /rara-menthenic aldehydes with about 90% combined yields under relatively mild conditions (80 C, 80 atm) (Scheme 6.32) [119]. y-Terpinene is a naturally occurring compound. In a pure state, it is a colorless, pine-like fragrant oil, which is contained in many essential oils, especially citrus and spice. 

Hirano and Hayashi have introduced a novel fragrant fiber and yam based on chitosan. A bundle of two silk fibroin filaments was coated with a layer of N-modified chitosan using fragrant aldehydes such as cinnamaldehyde. A portion of chitosan fiber was suspended in methanol and a fragrant aldehyde was added. The mixture was kept at room temperature for 18 hours, washed with methanol, filtered, and air-dried. The fragrant derivatives, fibers, and yarns are suggested to be useful as a novel biomaterials in a wide field of applications, including air-filters, cosmetics, and textiles [52]. 

The perfume industry makes considerable use of naturally occurring substances such as those obtained from rose and jasmine extracts. In many cases, the quantities of fragrant oils available by natural product isolation are so small that it is necessary to synthesize them. Examples are the olfactory components of violets, which include fro s-2-cis-6-nonadien-l-ol and the corresponding aldehyde. An intermediate in their large-scale synthesis is cis-3-hexen- l-ol, whose industrial preparation is described as a closely guarded secret. Using the methods in this and the preceding sections, propose a synthesis from 1-butyne. 

The preceding survey of the recent developments in the synthesis of CICs and their application in small molecules and bioactive natural products reflects an active current interest in this highly versatile class of useful reagents. From a practical point of view, CICs have revolutionized the application of IMCRs, in particular that of U-4CR, due to their mild removal conditions that are compatible with many commonly used functional handles and their odorless, fragrant-like smell. Post-Ugi modification using CICs provides a method of transforming Af-terminal secondary amides into carboxylic acids, esters, thioesters, ketones, aldehydes, and alcohols for further chemical diversification and thus helped remedy the lack of commercial isocyanide inputs. 

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