Side chains, on aromatic

In model compounds, the aliphatic side chains on aromatic nuclei transalkylate without rearrangement s ll However, the reaction of aliphatic bridges is more complicated. For example, transalkylation of l-(4-methoxyphenyl)-3-(2-naphthyl)... 

Oxidative degradation of long aliphatic side chains on aromatic or heterocyclic... 

Ammonia reacts catalytically with alkyl or alkanyl side chains on aromatic hydrocarbons to form aromatic nitriles, or with olefins, and to some extent alkanes, to form aliphatic nitriles. It also reacts catalytically with methane (natural gas) in the presence of a regulated amount of oxygen to form hydrogen cyanide. The following equations illustrate the reactions involved with substituted aromatic compounds ... 

Beside,s the A-methyl group, alkyl substituents in other parts of CM molecules can also be hydroxylated. For example, the alkyl chain in chiorpropham can be hydroxylated and then further carboxyiated (Bobtk el al 1972). The alkyl side chain on aromatic rings of CMs, such as mctol-carb and butacarb, can also be hydroxylated (Kuhr and Dorough, 1976b Kulkarni and Hodgson, 1980). Further oxidation of the hydroxylated methyl groups to carboxylic acids is also observed (Fig. 5). 

Organic acids can be prepared in many ways, four of which are described here (1) oxidation of primary alcohols or aldehydes, (2) oxidation of alkyl side chains on aromatic rings, (3) reaction of Grignard reagents with carbon dioxide, and (4) hydrolysis of alkyl cyanides (nitriles). 

Partial oxidations of side chains on aromatic compounds have also been achieved using tetraalkylammonium permanganates in organic solvents. 

Perhaps the most familiar and useful hydrocarbon oxidation is the oxidation of side chains on aromatic rings. Two factors contribute to making this a high-yield procedure, despite the use of strong oxidants. First, the benzylic site is activated to oxidation. Either radical or carbocation intermediates can be stabilized by resonance. Second, the aromatic ring is resistant to attack by Mn(VII) and Cr(VI) reagents which oxidize the side chain. Scheme 12.14 provides some examples of the familiar oxidation of aromatic alkyl substituents to carboxylic acid groups. 

Important industrial products are manufactured by direct oxidation of aromatic rings as well as by the selective oxidation of alkyl side chains on aromatic hydrocarbons (Figs. 3 and 4j. 

A primary or secondary alkyl side chain on an aromatic ring is converted to a carboxyl group by reaction with a strong oxidizing agent such as potassium permanga nate or chromic acid... 

Alkyl Side Chains of Aromatic Rings. The preferential position of attack on a side chain is usually the one a to the ring. Both for active radicals such as chlorine and phenyl and for more selective ones such as bromine such attack is faster than that at a primary carbon, but for the active radicals benzylic attack is slower than for tertiary positions, while for the selective ones it is faster. Two or three aryl groups on a carbon activate its hydrogens even more, as would be expected from the resonance involved. These statements can be illustrated by the following abstraction ratios ... 

Compounds with conformationally restrained side chains, unsaturated side chains and aromatic side chains have been synthesised in order to better define the steric requirements of the binding site in the side-chain region. These are shown in Table 6.9. On average, the conformationally restrained... 

The effect of the position of side chains on the intercalation kinetics of anthra-quinones,101 which are related to the aromatic moiety of daunomycin (13), was studied with the stopped flow SDS sequestration technique. Guest molecules 14—17 can have two different intercalation modes, a classic mode where both side chains are located in the same groove of the DNA helix (14 and 16) or a threading mode where the side chains are located in opposite grooves of the DNA (15 and 17) (Scheme 7). The relative position of intercalated 14 with respect to the DNA bases was suggested to be the same as for 13. 

Aromatic hydrocarbons Benzene systems Condensed aromatic systems Condensed aromatic-cycloalkyl systems Alkyl side chains on ring systems... 

While functional (immunological) mimicry has been established, the basis of mimicry on the molecular level remains to be explained. Several hypotheses have been put forward one of the earliest was that the side chains of aromatic amino acid residues might mimic the hydrophobic faces of the pyranosyl rings of carbohydrates. Before 1997, no structural evidence was available to support or discount these hypotheses. The nature of peptide-carbohydrate mimicry on the molecular level became the subject of structural investigations, and the resulting studies along with functional data will be discussed below. 

Triple bonds in side chains of aromatics can be reduced to double bonds or completely saturated. The outcome of such reductions depends on the structure of the acetylene and on the method of reduction. If the triple bond is not conjugated with the benzene ring it can be handled in the same way as in aliphatic acetylenes. In addition, electrochemical reduction in a solution of lithium chloride in methylamine has been used for partial reduction to alkenes trans isomers, where applicable) in 40-51% yields (with 2,5-dihydroaromatic alkenes as by-products) [379]. Aromatic acetylenes with triple bonds conjugated with benzene rings can be hydrogenated over Raney nickel to cis olefins [356], or to alkyl aromatics over rhenium sulfide catalyst [54]. Electroreduction in methylamine containing lithium chloride gives 80% yields of alkyl aromatics [379]. 

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]. 

---