Naturally Occurring Aldehydes and Ketones

Figure 21.6 Some naturally occurring aldehydes and ketones with strong odors citral...

The ketones are excellent solvents. Acetone is very useful because it dissolves most organic compounds yet is miscible with water. Acetone is widely used as a solvent in the manufacture of lacquers, paint removers, explosives, plastics, drugs, and disinfectants. Some ketones of high molecular weight are used extensively in blending perfumes. Structures of some naturally occurring aldehydes and ketones are... 

A number of naturally occurring aldehydes and ketones play important roles within living systems. The carbonyl functional group is fairly common in biological compounds. For example, progesterone and testosterone, female and male sex hormones, respectively, are both ketones. 

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). 

Formaldehyde is a key industrial chemical in the production of plastics such as Bakelite and Formica. Acetone is an important solvent. Some naturally occurring aldehydes and ketones are important in living systems. Some function as sex hormones others are used as flavorings. 

A (a) List several naturally occurring aldehydes and ketones, (b) What are their sources (c) What are some uses of these compounds ... 

Many compounds found in nature possess an aldehyde or ketone functional group. Vanilla and cinnamon flavorings are naturally occurring aldehydes. The ketones carvone and camphor impart the characteristic flavors of spearmint leaves and caraway seeds. 

The reaction conditions proved to be remarkably mild and even highly sensitive substrates such as ( )-croton aldehyde could be converted into the corresponding aryl ketone. The procedure is also applicable for the aiylation of naturally occurring aldehydes, and this has been demonstrated by the coupling of enantiomerically pure (S)-citronellal. The group of Cheng developed a complementary Pd(OAc)2-catalyzed aerobic protocol that is highly efficient for the acylation of 2-phenylpyridine derivatives with electron-rich, electron-deficient and heterocyclic aromatic aldehydes (Scheme 1.39). ... 

Many occur naturally In terms of both variety and quantity aldehydes and ketones rank among the most common and familiar natural products Several are shown m Figure 17 4... 

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... 

Acetalation. As polyhydroxy compounds, carbohydrates react with aldehydes and ketones to form cycHc acetals (1,13). Examples are the reaction of D-glucose with acetone and a protic or Lewis acid catalyst to form l,2 5,6-di-0-isoprop5lidene-a-D-glucofuranose [582-52-5] and its reaction with benzaldehyde to form 4,6-0-benzyhdene-D-glucopyranose [25152-90-3]. The 4,6-0-(l-carboxyethyhdine) group (related to pymvic acid) occurs naturally in some polysaccharides. 

There are two types of electronic transition commonly responsible for photochemically induced reactions in organic molecules. The first of these is the n—>ir transition in which an electron in a nonbonding atomic orbital is excited to an antibonding ir orbital, the excited state being referred to as n, it. This occurs in nitrogen-, oxygen-, and sulfur-containing molecules, and the nature of the n, 77 state of the carbonyl function has been the subject of considerable study.5,6 Excitation to the n, tt state in aldehydes and ketones occurs at approximately 290 nm. 

Formaldehyde, acetaldehyde, and acetone are important commercial chemicals, synthesized by special methods. In the laboratory, aldehydes and ketones are most commonly prepared by oxidizing alcohols, but they can also be prepared by hydrating alkynes and by Friedel-Crafts acylation of arenes. Aldehydes and ketones occur widely in nature (see Figure 9.1). 

Aldehydes and ketones of low molecular weight have commercial importance. Many others occur naturally. Table 31.1 has some representative examples. 

Aldehydes and ketones are also important components of many fragrances and flavors. For example, butanal (butyraldehyde) is used to impart a buttery flavor to margarine and other foods. Because aldehydes are slowly oxidized to carboxylic acids by the oxygen of air, it is readily apparent how the odor of rancid butter arises. Although a-pentylcinnamaldehyde does not occur naturally, it has been found to have a powerful jasmine odor and is used in many perfumes and soaps, a-lonone is a naturally oc-... 

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