Aromatic compound cleavage

In alkyl-substituted aromatic compounds, cleavage is very probable at the bond /3 to the ring, giving the resonance-stabilized benzyl ion or, more likely, the tropylium ion ... 

A new germanium-based hnker has been developed for solid-phase synthesis of aromatic compounds. Cleavage from the polymer support via ipso-degerrnylalion with TFA, Id, Bry, and NCS provides protio, bromo, and chloroaryl compounds, respectively (Scheme 11.55) [78]. 

DMSO, NaCN, 125-180°, 5-48 h, 65-90% yield.This cleavage reaction is successful for aromatic systems containing ketones, amides, and carboxylic acids mixtures are obtained from nitro-substituted aromatic compounds there is no reaction with 5-methoxyindole (180°, 48 h). 

Molecular chlorine is believed to be the active electrophile in uncatalyzed chlorination of aromatic compounds. Simple second-order kinetics are observed in acetic acid. The reaction is much slower in nonpolar solvents such as dichloromethane and carbon tetrachloride. Chlorination in nonpolar solvents is catalyzed by added acid. The catalysis by acids is probably the result of assistance by proton transfer during the cleavage of the Cl-Cl bond. ... 

Step 1 above requires that there be bonds in the coal that are weak enough to break in appropriate numbers at conversion temperatures and times. Table I displays some kinetic data for the cleavage of benzylic bonds in a series of increasingly aromatic compounds. In accord with expectation, an extension of the aromatic system increases the ease with which the benzylic bond is broken. 

Some experiments were conducted to determine the influence of the solution pH. The catalytic oxidation of p-coumaric acid has been performed by increasing the initial pH from 3.5 to 7.5 and 11. Although the cleavage of the exocyclic double bond may be pH sensitive we obtained the same major intermediates which are the hydroxybenzaldehyde and the p-hydroxybenzoic acid molecules. The rate of oxidation of these aromatic compounds to ring opening compounds was higher when the initial pH was basic and yielded higher concentrations of maleic and fumaric acids. 

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