Arylalkane

An aryl alkyl ketone 1 can be converted into an tn-arylalkane carboxylic amide 2 by employing the Willgerodt reaction The number of carbon centers is retained. The reaction is carried out by treating the ketone with an aqueous solution of ammonium polysulfide. A variant that has been developed by Kindler, and which is called the Willgerodt-Kindler reaction, uses a mixture of sulfur and a secondary amine instead of the ammonium polysulfide. 

IR, 2S )- or (1 / , 2R )-2-Acyl-I-amino-l-arylalkanes anti-4 General Procedure38-42 ... 

Alkanes, arylalkanes, and cycloalkanes can be aminated, at tertiary positions only,... 

Aromatics react with olefins very readily when potassium is used as a catalyst. However, potassium is less selective in catalyzing alkylation than sodium because an additional reaction yields indans, as reported by Schaap and Pines 24). Therefore, the products consist of mixtures of arylalkanes and indans the relative amount of each depends largely on the aromatic used (as shown in Table II). The degree of alkyl substitution of the o -carbon... 

The side-chain alkylation reaction of aromatic hydrocarbons has also been studied using unsaturated aromatic olefins, especially styrene. Pines and Wunderlich 43) found that phenylethylated aromatics resulted from the reaction of styrenes with arylalkanes at 80-125° in the presence of sodium with a promoter. The mechanism of reaction is similar to that suggested for monoolefins, but addition does not take place to yield a primary carbanion a resonance stabilized benzylic carbanion is formed [Reaction (23a, b)j. 

A possible mechanism of oxidation of methylene groups to carbonyl groups involves autoxidation (oxidation by molecular oxygen) at the benzylic position. Autoxidation of arylalkanes is a facile reaction with low activation energies for example, 6.0 kcal/mole for 1,1-diphenylethane and 13.3 kcal/mole for toluene. ... 

Oxygen abstraction reactions from alcohols, ketones, acyl halides and other oxygen-containing compounds by MCI or related derivatives also afforded a route to relatively simple complexes of the oxo halides (Table 24). Thus Nb2Cli0 was found to abstract oxygen from higher ketones to yield, after hydrolysis, alkanes, chloroalkanes or arylalkanes.414... 

Side-Chain Isomerization. Arylalkanes undergo acid-catalyzed isomerization in the side chain in a way similar to the skeletal rearrangement of alkanes.70-72 There are, however, notable differences. Propylbenzene, for instance, yields only a small amount (a few percentages) of isopropylbenzene 73 Similarly, sec-butyl- and iso-butylbenzene are interconverted at 100°C with wet A1C13, but only a negligible amount of tert-butylbenzene is formed.74 In the transformation of labeled propylbenzene the recovered starting material was shown to have equal amounts of labeling in the a and p positions of the side chain, but none in the y position 73... 

Positional Isomerization. A different type of isomerization, substituent migration, takes place when di- and polyalkylbenzenes (naphthalenes, etc.) are treated with acidic catalysts. Similar to the isomerization of alkanes, thermodynamic equilibria of neutral arylalkanes and the corresponding carbocations are different. This difference permits the synthesis of isomers in amounts exceeding thermodynamic equilibrium when appropriate reaction conditions (excess acid, fast hydride transfer) are applied. Most of these studies were carried out in connection with the alkylation of aromatic hydrocarbons, and further details are found in Section 5.1.4. 

Styrene reacts with arylalkanes to yield mono- and diadducts with the concomitant formation of polymeric byproducts.243 a-Methylstyrene and p-methylstyrene, in turn, give monoadducts in high yields.244,245... 

Free-radical side-chain chlorination of arylalkanes in the benzylic position can be effected by chlorine or S02C12. Phosphorus pentachloride is also capable of effectively catalyzing side-chain chlorination. 

Side-Chain Chlorination of Arylalkanes. Alkyl-substituted aromatic compounds can easily be halogenated at the benzylic position with chlorine or bromine.107 108,142 143 a-Monohaloalkylaromatics are usually the main products with both reagents. 

Olah151 and later Messina152 found that PCI5 is a highly effective catalyst for the free-radical side-chain chlorination of arylalkanes. Chlorination in hydrocarbon or chlorinated solvents or without solvent at room temperature yields a monochlo-rinated products with high selectivity. When the reaction was carried out in polar solvents such as nitromethane and nitrobenzene, only ring chlorination occurred. 

The oxidative effects of silver(II) complexes of pyridine carboxylates have been studied for a variety of substrates. With ar-amino acids, a rapid reaction occurred at 70 °C in aqueous solution with bis(pyridyl-2-carboxylato)silver(II). 4 The product was the next lower homologous aldehyde and yields were generally greater than 80%. Other substrates included primary and secondary amines, alcohols, monosaccharide derivatives, alkenes, arylalkanes and arylalkanols.90 Only minor differences were detected in efficiencies when 2-, 3- or 4-mono-, or 2,3-di-carboxylates were used as the oxidant. 

Because r is larger than r then a linear plot ofln k vs. 1 /eR with a positive slope will be obtained irrespective of the charge on the ion. The observation3 that a positive slope of log/c vs. l/sR was obtained for the oxidation of triphenylmethane and diphenylmethane by [Fe(CN)6]3 in various mixtures of aqueous acetic acid was taken as proof that the rate determining step was of the ion dipole type, i.e. involved [Fe(CN)6]3- and the arylalkane molecule. 

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