Aliphatic side-chain oxidation

Mechanism The mechanism of the aliphatic side-chain oxidation as shown in Scheme 7.34 probably involves manganese-oxygen-carbon bonding with subsequent reduction of manganese and oxidation of carbon to yield aldehyde, which is much more vulnerable to oxidation with permanganate. 

The microsomal oxidations encountered include aliphatic side chain oxidations, aromatic hydroxylations, N-dealkylations, O- and S-dealkylations (which may also be viewed as ether cleavages), N-oxidations to N-oxides, and N-hydroxylations, and oxidation of divalent sulfur to sulfoxides. Representative examples are given in Table 3-1. 

When an aromatic compound having an aliphatic side chain is subjected to oxidation, fission of the side chain occurs between the first and second carbon atoms from the benzene ring, the first carbon atom thus becoming part of a carboxyl ( -COOH) group. For example ... 

With regard to the results of our infrared study, a word of caution is appropriate. The large decreases in the concentration of the aliphatic bridges after oxidation, as measured by transalkylation (Table III), cannot be expected to match those indicated in the difference infrared spectra between oxidized and fresh coals. This is because the spectra measure the total aliphatic content of the samples, namely aliphatic bridges, hydroaromatics, and aliphatic side chains. In contrast, results in Table II show differences in relative concentrations of the aliphatic bridges, which represent only a part of the total aliphatics. Furthermore, concentrations measured by transalkylation correspond to only the soluble fractions of the reaction products some of the more complex transalkylation products may be retained in the residue itself. 

In an earlier experiment, Jori et al. (14) reported that methionyl residues are important in maintaining the tertiary structure of lysozyme. The introduction of a polar center into the aliphatic side chain of methionine, as a consequence of the conversion of the thioether function to the sulfoxide, may bring about a structural change of the lysozyme molecule which, in turn, reduces the catalytic efficiency. When ozonized lysozyme was treated with 2-mercaptoethanol in an aqueous solution according to the procedure of Jori e al. (14), the enzyme did not show any increase in its activity. This may be explained in two ways. In one, such reactions are complicated by many side reactions, e.g. sulfhydryl-disulfide interchange, aggregation and precipitation of the modified enzyme (24-26). In the other, the failure to recover the activity of the enzyme may by associated with the extensive oxidation of other residues. 

Aliphatic side chains of aromatics, such as cumene [65] and ethylbenzene [66] are oxidized to the corresponding alcohols and ketones by oxygen on FePcY and CoPcY respectively (Scheme 4). Propylene is oxidized on CoPcX to small amounts of carbon dioxide and acetone and higher amounts of formaldehyde and acetaldehyde [79]. 

Reaction C. Oxidation of the Side Chain in Aromatic Compounds. (A., 122,184 133, 41 137, 308 141,144 147, 292 B., 7,1057 19, 705 Z. Ch., 4, 119) (Fittig).—When aromatic compounds containing aliphatic side chains attached to the nucleus are treated with certain oxidising agents (potassium permanganate, dilute nitric acid, and chromic acid), the side chain is oxidised until only a carboxylic group attached to the nucleus remains the end methyl group, if there are several carbon atoms... 

Changes in aliphatic side chains are mainly initiated by the abstraction of a hydrogen atom from a C-H bond. This produces a free radical which in the absence of O2 can combine with similar free radicals to give dimerization products or with CO2 [probably the CO2 ion. (40)] to give monoamino-dicarboxylic acids. In oxygen these are replaced by oxidative reactions which produce carbonyl, hydroxyl, and carboxyl groups through hydro-peroxy intermediates ... 

Toluene tends to enter brain tissue, which it affects, and accumulates in adipose tissue. Unlike benzene, toluene possesses an aliphatic side chain that can be oxidized enzymatically, leading to products that are readily excreted from the body. The metabolism of toluene is thought to proceed via oxidation of the methyl group and formation of the conjugate compound hippuric acid, as shown in Figure 13.9. 

It is very easy to oxidize aliphatic side chains attached to aromatic rings than the side ring themselves. Alkaline KMn04 and dichromate convert the alkyl group attached to the... 

In its reactions with organic molecules, OH behaves as an electrophile whereas 0 is a nucleophile. Thus, like H (see above), OH readily adds to double bonds but 0 does not however, both forms of the radical abstract H from C-H bonds. In the case of an aromatic molecule carrying an aliphatic side chain, OH adds preferentially to the aromatic ring and 0 abstracts H from the side chain this can result in a change of reaction mechanism when the pH is raised so that 0 replaces OH as the oxidant. 

It is known as cuminic aldehyde because of its occurrence in Roman oil of cumin. It oxidizes to an aromatic acid known as cuminic acid which is para iso-propyl benzoic acid. On further oxidation the aliphatic side chain is likewise oxidized to carboxyl and a di-basic acid, terrephthalic acid, results. This acid is obtained by the complete oxidation of para-xylene and hence is a para compound. This establishes cuminic aldehyde as a para compound also. 

Cinnamic Aldehyde.—The other aromatic aldehyde which we shall mention is cinnamic aldehyde. It contains the aldehyde group in the side chain and not in the benzene ring, and is thus an aliphatic aldehyde substitution product of benzene. The aliphatic side chain is also an unsaturated chain. Its formula is CeHs—CH=CH—CHO, and it may be considered as beta-phenyl acrylic aldehyde. As an aldehyde it yields by oxidation an acid, viz., beta-phenyl acrylic acid or, as it is commonly known, cinnamic acid. The aldehyde is found in oil of cinnamon obtained from cinnamon bark, hence its name and the name of the acid. The most important synthesis is by the condensation of benzaldehyde and acetaldehyde, as follows ... 

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