Aldehydes and Acetals

Aliphatic aldehydes are among the most important components used in perfumery. Although the lower fatty aldehydes C2-C7 occur widely in nature, they are - with the exception of hexanal - seldom used in fragrance compositions. The lower 

In addition to the straight-chain saturated aldehydes, a number of branched-chain and unsaturated aliphatic aldehydes are important as fragrance and flavoring materials. The double unsaturated 2-tr zra-6-cw-nonadienal [557-48-2, violet leaf aldehyde (the dominant component of cucumber aroma), is one of the most potent fragrance and flavoring substances it is, therefore, only used in very small amounts. 2-fr zra,4-tr(zra-Decadienal [25152-84-5] with its specifically fatty odor character is indispensible in chicken meat flavor compositions. 

Acetals derived from aliphatic aldehydes have odor characteristics that resemble those of the aldehydes but are less pronounced. These acetals contribute to the aroma of alcoholic beverages, but can rarely be used in flavoring compositions because they are not sufficiently stable. Since they are resistant to alkali, a number of them (e.g., heptanal dimethyl acetal and octanal dimethyl acetal) are occasionally incorporated into soap perfumes. 

Fatty aldehydes are generally produced by dehydrogenation of alcohols in the presence of suitable catalysts. The alcohols are often cheap and available in good purity. Aldehyde synthesis via the oxo process is less suitable since the resultant products are often not pure enough for flavor and perfume purposes. Specific syntheses for the branched-chain and unsaturated aldehydes that are important in perfumery and flavoring techniques are described under the individual compounds. 

Hexanal is used in fruit flavors and, when highly diluted, in perfumery for obtaining fruity notes. 

Aliphatic aldehydes are among the most important components used in perfumery. Although the lower fatty aldehydes C2-C7 occur widely in nature, they are - with the exception of hexanal - seldom used in fragrance compositions. The lower aldehydes (e.g., acetaldehyde, isobutyraldehyde, isovaleraldehyde, and 2-methyl-butyral-dehyde) impart fruity and roast characters to flavor compositions. Fatty aldehydes C8-C13, however, are used, singly or in combination, in nearly all perfume types and also in aromas. Their odor becomes weaker with increasing molecular mass, so that aldehydes Ci3 are not important as perfume ingredients. 

CH3(CH2)4CHO, C6H120, Mr 100.16, 6p10i.3kPa 128 °C, 4° 0.8139, rag0 1.4039, occurs, for example, in apple and strawberry aromas as well as in orange and lemon oil. It is a colorless liquid with a fatty-green odor and in low concentration is reminiscent of unripe fruit. 

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In similar work, CF3CCI2CO2CH3 yields methyl a-trifluoromethyl-a,(i-un-saturated carboxylates when reacted with a zinc-copper couple, aldehydes, and acetic anhydride [67] (equation 55). This methodology gives (Z)-a-fluoro-a- -un-saturated carboxylates from the reaction of carbonyl compounds with CFCI2CO2CH3 and zinc and acetic anhydride [6 ]. 

Fig.i General biosynthetic pathways for the production of alcohol, aldehyde, and acetate ester pheromone components in female moths. Top production of saturated fatty acids. Middle production of monounsaturated fatty acids and limited chain shortening produces intermediate compounds that can be reduced to an alcohol. Aldehyde and acetate ester pheromones are produced by an oxidase and acetyl-transferase, respectively. Bottom biosynthetic pathway for the production of the acetate ester pheromone components in the cabbage looper moth, Trichoplusia ni. The CoA derivatives are reduced and acetylated to form the acetate esters. Additional pheromone components include 12 OAc and ll-12 OAc... 

Production of acetate ester pheromone components utilizes an enzyme called acetyl-CoA fatty alcohol acetyltransferase that converts a fatty alcohol to an acetate ester. Therefore, alcohols could be utilized as substrates for both aldehyde and acetate ester formation. In some tortricids an in vitro enzyme assay was utilized to demonstrate specificity of the acetyltransferase for the Z isomer of ll-14 OH [66]. This specificity contributes to the final ratio of... 

Complex 64 is unstable at room temperature even as a solid and is easily hydrolyzed in neutral water to produce glycol aldehyde (Eq. (17)). In 0.1 M HC104, 64 produces glycol aldehyde and acetic acid in a ca. 9 1 ratio. 

Circulation flow system, measurement of reaction rate, 28 175-178 Clausius-Clapeyron equation, 38 171 Clay see also specific types color tests, 27 101 compensation behavior, 26 304-307 minerals, ship-in-bottle synthesis, metal clusters, 38 368-379 organic syntheses on, 38 264-279 active sites on montmorillonite for aldol reaction, 38 268-269 aldol condensation of enolsilanes with aldehydes and acetals, 38 265-273 Al-Mont acid strength, 38 270-271, 273 comparison of catalysis between Al-Mont and trifluorometfaanesulfonic acid, 38 269-270... 

Cinnamic acid synthesis from aryl aldehyde and acetic anhydride. 

Brabec MJ Aldehydes and acetals. In Clayton GD, Clayton FE (eds) Patty s Industrial Hygiene and Toxicology, 3rd ed, Vol 2A, Toxicology, pp 2665-2666. New York, Wiley-Interscience, 1981... 

Section B of Scheme 9.4 gives some additional examples of Lewis acid-mediated reactions of allylic silanes with aldehydes and acetals. 

Wenkert and Khatuya (51) examined the competition between direct insertion of a carbene into furan (via cyclopropanation) and ylide formation with reactive side-chain functionality such as esters, aldehydes, and acetals. They demonstrated the ease of formation of aldehyde derived carbonyl ylides (Scheme 4.30) as opposed to reaction with the electron-rich olefin of the furan. Treatment of 3-furfural (136) with ethyl diazoacetate (EDA) and rhodium acetate led to formation of ylide 137, followed by trapping with a second molecule of furfural to give the acetal 138 as an equal mixture of isomers at the acetal hydrogen position. 

Aldol reactions.1 The anion generated (BuLi) from chromium carbene complexes undergoes aldol reactions with aldehydes or ketones activated by a Lewis acid. Best results are obtained with ketones in the presence of BF3 etherate, whereas TiCl4 is the preferred catalyst for aldehydes and acetals. 

The mechanism of the Perkin condensation involving benzal acetate has been revised.17 It has been demonstrated that the enolate of the gem-diacetate derived from the aromatic aldehyde and acetic anhydride-rather than the enolate of acetic anhydride itself-adds to the aldehyde in the key step. The deprotonation of the diacetate to the enolate appeared to be assisted electrophilically by the neighbouring acetate group. 

An ingenious new method for the preparation of Woodward s intermediate (97) by Pearlman70 constitutes another formal synthesis of reserpine. The essence of this new approach is an adaptation of the de Mayo reaction which allows the introduction of vicinal aldehyde and acetic ester functions on to a double-bond (Scheme 13). An internal [2tt + 27r] photocyclization of the diene (98) gave the tetracyclic cyclobutane derivative (99), which was converted into the ester (100) by standard procedures. Methanolysis of the acetate function with concomitant retro-aldol fission completed the introduction of the vicinal aldehyde and acetic ester functions obvious manipulation then gave the desired intermediate (97). 

Vanadium pentoxide has received limited application as an oxygen carrier. Its presence accelerates the oxidation of ethyl alcohol to aldehyde and acetic acid, when effected by air or by oxygen. 

Tungstic oxide at 350° is reduced to a blue oxide which has a dehydrating effect and ethylene results as well as aldehyde and acetic acid. 

Thus, the majority of known lepidopteran pheromones are comprised of compounds that are between 10 and 23 carbons in length, with one or no polar functional groups. Within these broad limits, there are two major structural classes, each of which arises from different biosynthetic pathways. The first class, designated as Type I pheromones (Ando et al., 2004) consists primarily of alcohols, aldehydes, and acetates with unbranched carbon chains of 10-18 carbons, and with 0-3 double bonds. Unusual structures or functional groups, such as triple bonds, nitro groups, or esters other than acetates, are occasionally... 

Reaction with RCHO and acetals.1 In the presence of dibutyltin bis(tri-fiuoromethanesulfonate), 2,3 this reagent converts aldehydes or their dialkyl acetals or ethylene acetals into 2-alkyl-1,3-dithianes (70-85% yield). However, the reagent differentiates between aldehydes and acetals as shown in the examples. An aliphatic... 

Finely divided ruthenium acts as a catalyser, inducing, for example, the oxidation of alcohol to aldehyde and acetic acid in the presence of air. 

Trichloroalane in dichloromethane cleaves isopropyl aryl ethers leaving methyl aryl ethers intact. A variety of functional groups (aryl halides, 1,1-dihaloalkenes, aldehydes and acetates) withstand the reaction conditions but alkynes and TIPS ethers do not survive. Scheme 4 110 illustrates an application of the reaction to a synthesis of the Fagaronine alkaloids,201 TVichloroborane in dichloromethane may also be used for the deprotection of isopropyl ethers.202... 

Despite the obvious improvements achieved in the hydrocarbonylation of methanol, several problems remain to be solved before a technical realization of this process is achieved. One serious drawback is the formation of side products. Tlie liquid phase contains not only alcohols, aldehydes and acetals but also ethers, acetates, and minor amounts of acetic add accompanied by the... 

Condensation of 3 (2 1)-pyridazinones with aromatic aldehydes and acetic anhydride gives condensation products for which structures of type 92 have been assigned. ... 

Show by formulas the relation between ethyl alcohol, acetic aldehyde, and acetic acid, and by equations the possibility of passing from one to the other. 

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