Aromatic acids electron-donating groups

The phenylacetic acid derivative 469 is produced by the carbonylation of the aromatic aldehyde 468 having electron-donating groups[jl26]. The reaction proceeds at 110 C under 50-100 atm of CO with the catalytic system Pd-Ph3P-HCl. The reaction is explained by the successive dicarbonylation of the benzylic chlorides 470 and 471 formed in situ by the addition of HCl to aldehyde to form the malonate 472, followed by decarboxylation. As supporting evidence, mandelic acid is converted into phenylacetic acid under the same reaction conditions[327]. 

The decarboxylation of aromatic acids is most often carried out by heating with copper and quinoline. However, two other methods can be used with certain substrates. In one method, the salt of the acid (ArCOO ) is heated, and in the other the carboxylic acid is heated with a strong acid, often sulfuric. The latter method is accelerated by the presence of electron-donating groups in ortho and para positions and by the steric effect of groups in the ortho positions in benzene systems it is... 

This is because of greater electronegativity of sp hybridised carbon to which carbojyl carbon is attached. The presence of electron withdrawing group on the phenyl of aromatic carbojylic acid increases their acidity whUe electron donating groups decrease their acidity. 

Through a slight modification the Pomeranz-Fritsch synthesis can be made particularly useful for the preparation of 1,2-dihydroisoquinolines. The imine is first reduced with sodium borohydride in 98% ethanol to the corresponding benzylamine, prior to cyclization, by treatment with 6 M hydrochloric acid. When electron-donating groups (such as a methoxyl) are present in the aromatic unit of the benzylamine, the ring-... 

Eclipsed conformation, 7, 254 Electrocyclic reactions, 341, 344-348 Electrol ic oxidation, 307 Electrolytic reduction, 307 Electromeric effect, 24 Electron configuration, 3 Electron density, 21, 26, 29, 393 Electron-donating groups, 23, 26 addition to 0=C and, 183 addition to 0=0 and, 205, 206 aromatic substitution and, 153, 158 pinacol change and, 115 Electronegativity, 21, 22, 95 Electrons, lone pair, 10, 72 Electron spin, paired, 2, 308 Electron-withdrawing groups, 23 acidity and, 59, 61, 62, 272... 

The addition of electrons to an aromatic system can be accomplished by adding electron-donating groups or by changing the pH of the solution. The effect of pH on the fluorescence of 1-naphthol is well known. In acidic or neutral media the molecule exists as the form 1 ... 

The reaction rate differences are readily rationalised from a consideration of fundamental reaction mechanism principles (e.g. electron-donating groups increase electron density in the aromatic ring and thus hinder acceptance of an electron) the regioselectivity of the reduction is explained from a consideration of the relative stabilities of the possible alternative mesomeric intermediates, these being (44) in the case of anisole and (45) in the case of benzoic acid. 

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