Aromatic Aldehydes, Ketones and Alcohols

Aromatic aldehydes and ketones show the usual reactions associated with a carbonyl group, but they display further reactions arising from the influence of the aromatic environment. This chapter describes synthetic routes to and the chemistries of benzaldehyde (1) and acetophenone (phenylethanone, 2) and their derivatives. 

Aromatic aldehydes and ketones show the usual reactions associated with t i k coMe 

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Following the initial isolation of the Hnl from M. esculenta [33] in which the peptide sequence was established, an overexpressed version of this enzyme (in E. coli) was prepared [41]. This system is not limited for enzyme quantity (as outlined in Sect. 2.3), and can accept a wide range of aromatic, heterocyclic and aliphatic aldehydes, as well as ketones, as substrates. In practical terms, a measure of the degree of enzyme inhibition by substrates is of significant value and for this system this has been quantified for a range of aldehydes, ketones and alcohols [70]. It was deduced that ketones and alcohols are competitive inhibitors, whilst aldehydes are noncompetitive inhibitors. 

Typical examples of VOCs for indoor air include ketones from lacquers, varnishes, and adhesives aldehydes, ketones, and alcohols from cosmetics ethers from resins and paints terpenes from polishes, fabrics, fabric softeners, cigarettes, and food and carbon tetrachloride from industrial cleaners. Usually they mix in the indoor atmosphere at the level of ppm. However, their reactivity is different and varies in the following order alcohols > aldehydes > aromatics > ketones > alkenes > alkanes [61]. 

About 300 volatile compounds are present in honey and more than 200 have been identified. There are esters of aliphatic and aromatic acids, aldehydes, ketones and alcohols. Of importance are especially P-damascenone and phenylacetaldehyde, which have a honey-like odor and taste. Methyl anthranilate is typical of the honey from citrus varieties and lavender and 2,4,5,7a-tetrahydro-3, 6-dimethylbenzofuran (Formula 19.4, linden ether) is typical of linden honey. 

Peroxomonosulfuric acid oxidi2es cyanide to cyanate, chloride to chlorine, and sulfide to sulfate (60). It readily oxidi2es carboxyflc acids, alcohols, alkenes, ketones, aromatic aldehydes, phenols, and hydroquiaone (61). Peroxomonosulfuric acid hydroly2es rapidly at pH <2 to hydrogen peroxide and sulfuric acid. It is usually made and used ia the form of Caro s acid. 

Reaction with Organic Compounds. Aluminum is not attacked by saturated or unsaturated, aUphatic or aromatic hydrocarbons. Halogenated derivatives of hydrocarbons do not generally react with aluminum except in the presence of water, which leads to the forma tion of halogen acids. The chemical stabiUty of aluminum in the presence of alcohols is very good and stabiUty is excellent in the presence of aldehydes, ketones, and quinones. 

In contrast to phenolic hydroxyl, benzylic hydroxyl is replaced by hydrogen very easily. In catalytic hydrogenation of aromatic aldehydes, ketones, acids and esters it is sometimes difficult to prevent the easy hydrogenolysis of the benzylic alcohols which result from the reduction of the above functions. A catalyst suitable for preventing hydrogenolysis of benzylic hydroxyl is platinized charcoal [28], Other catalysts, especially palladium on charcoal [619], palladium hydride [619], nickel [43], Raney nickel [619] and copper chromite [620], promote hydrogenolysis. In the case of chiral alcohols such as 2-phenyl-2-butanol hydrogenolysis took place with inversion over platinum and palladium, and with retention over Raney nickel (optical purities 59-66%) [619]. 

Thus, by a combination of oxidation by lignin peroxidases, Mn(II)-dependent peroxidases and other active oxygen species and reductions of some aromatic aldehydes, acids and ketones to the corresponding benzylic alcohols, all aromatic rings in the lignin polymer can be either converted to ring opened products or to quinones/hydroquinones. These products are then further metabolized to CO2 by a currently unknown mechanism. 

This section includes oxidations of alkanes and cycloalkanes, alkenes and cycloalkenes, dienes, alkynes, aromatic fluorocarbons, alcohols, phenols, ethers, aldehydes, ketones and carbohydrates, carboxylic acids, nitrogen compounds, and organoelement compounds, such as boron, phosphorus, sulfur, selenium, and iodine compounds, and steroids. 

A one-pot reaction has been developed for the reduction of aldehydes, ketones, and primary, secondary and tertiary alcohols into their corresponding alkyl function using either diethylsilane or n-butylsilane as the reducing agent in the presence of the Lewis acid catalyst tris(pentafluorophenyl)borane carbon-carbon double bonds remain unaffected.366 Aliphatic and aromatic polycarboxylic acids are also conveniently reduced to their corresponding alkanes using the same reagents and catalyst.367... 

Heat treatment of carotene under conditions which simulated several food processes led to the formation of aldehydes, ketones and low molecular weight aromatic and short-chain oxygenated hydrocarbons, many of which have been reported to be important flavor attributes of some foods, alcoholic beverages and tobacco. 

Phenol has been hydroxylated nearly quantitatively to hydroquinone 2 3 9 Most alkoxylations or hydroxylations of aromatics however either lead to anodic addition products (see Sect. 10.1) or to side chain substitution (see below). Specific side-chain hydroxylation is difficult to achieve because the alcohols formed as primary products are further oxidized to aldehydes, ketones and/or carboxylic acids. 

In considering the aromatic aldehydes and ketones and later the aromatic acids it should be emphasized that the relationships discussed in Part I (p. 129) between alcohols, aldehydes, ketones and acids are general and apply just as truly to the aromatic compounds as to the aliphatic. The class characteristics of alcohols, aldehydes, ketones and acids are the same in both series. Thus the primary alcohols, on oxidation, always yield first aldehydes and then acids, while the secondary alcohols yield ketones. 

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