Hydroxybenzoic acids formation

Treatment of p hydroxybenzoic acid with aqueous bromine leads to the evolution of carbon dioxide and the formation of 2 4 6 tnbromophenol Explain... 

First,/)-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) are acetylated to produce the low melting acetate esters which are molten at 200°C. In an inert gas, the two monomers are melted together at 200°C. The temperature is raised to 250—280°C and acetic acid is coUected for 0.5 to 3 h. The temperature is raised to 280—340°C and additional acetic acid is removed in vacuum for a period of 10 to 60 min. The opalescent polymer melt produced is extmded through a spinning jet, foUowed by melt drawdown. The use of the paraUel offset monomer, acetylated HNA, results in the formation of a series of random copolyesters of different compositions, many of which faU within the commercially acceptable melting range of... 

The rhodium catalyst previously discussed is employed in the hydrogenation of / -hydroxybenzoic acid. The resulting mixture of cis and trans products is separated by virtue of the ready formation of the lactone of the cis product, which is then hydrolized to the hydroxy acid. 

Gompper et al. (1968) determined the ratio of the two final products obtained from 2-diazoniobenzenecarboxylate in the presence of furan, namely the cycloaddition product 8.31 and 2-hydroxybenzoic acid (salicylic acid). This ratio depends on the water concentration but is independent of the concentration of added furan. This observation is consistent with the stepwise formation of benzyne (route A) involving... 

Sodium or potassium phenoxide can be carboxylated regioselectively in the para position in high yield by treatment with sodium or potassium carbonate and carbon monoxide. Carbon-14 labeling showed that it is the carbonate carbon that appears in the p-hydroxybenzoic acid product. The CO is converted to sodium or potassium formate. Carbon monoxide has also been used to carboxylate aromatic rings with palladium compoimds as catalysts. In addition, a palladium-catalyzed reaction has been used directly to prepare acyl fluorides ArH —> ArCOF. ... 

The reference intermolecular reaction for the aliphatic compounds is the formation of ethyl acetate from ethanol and acetic acid measured under the same conditions (20% ethanol-water, ionic strength 0.4 M) by Storm and Koshland (1972a). The esterification of benzoic acid in methanol at 25° is 290 times slower than that of acetic acid (Kirby, 1972), so this factor is used to correct the EM s, calculated otherwise in the same way, for the hydroxybenzoic acids. For the phenolic acids see notes m and n b Rate constants are in units of dm3 mol-1 s-1 c Storm and Koshland, 1972a d Storm and Koshland, 1972b Bunnett and Hauser, 1965... 

Table 11.3 lists the pseudo first-order rate constants for the decomposition of hydroxybenzoic acids. It shows that the ratio of the mean initial decomposition rate of HBAs under argon, R(HBA)Ar, to that under air, R(HBA)air, is equal to (3.0 + 4.9 + 5.1)/(2.7 + 3.4 + 3.1) = 1.4 (see Table 11.3). The ratio of the rate of OH radical formation under argon to that under air was estimated to be R( OH)Ar/.R( OH)air = 20/15 = 1.3 and is close to the value of R(HBA)Ar/R(HBA)air, which suggests that the decomposition of HBAs is mainly caused by OH radicals, and oxygen molecules have little effect on the decomposition.

Interestingly, it is possible to etherify hydroxybenzoic acids without the need to protect the carboxyl group (Scheme 6.19). The high charge delocalization of the car-boxylate obviously leads to a sufficient decrease of nucleophilicity to enable clean ether formation under certain conditions. During the planning of such reactions it should, however, be kept in mind that carboxylates can be O-alkylated under conditions similar to those required for the O-alkylation of phenols (see Section 6.9). 

Hydroxybenzoic acid (salicylic acid) does form a complex, although its formation is not favored when compared to that of the picolinato ligand. Presumably this, at least to an extent, reflects the fact that the chelate formed with salicylate has a six-membered ring, and six-membered chelates are much less favored than the five-membered analogue. 

Scheme 1. The divergent pathways for the oxidation ofp-hydroxybenzoate for formation of e.g., succinic acid...

The first fibers from a thermotropic liquid crystalline melt whose properties were reported were spun from a copolyester of para-hydroxybenzoic acid (PHB) and PET by workers at Tennessee Eastman Co. The preparation of the copolymer proceeds in two stages. First, / ara-acetoxybenzoic acid is reacted with PET in an acidolysis step to give a copolyester prepolymer, which in the second step is condensed further to a higher degree of polymerization suitable for fiber formation. 

The intramolecular hydrogen bond formation has just as important an influence on the chemical properties. Thus of the three isomeric hydroxybenzoic acids the ortho isomer, salicylic acid, is, as a result of the formation of hydrogen bonds in this substance, less readily soluble in water but more soluble in ether than two other isomers which have the same properties. The internal hydrogen bond formation has resulted in the action of the OH dipole outwards being diminished salicylic acid is as it were less polar than the other isomers although the total moment is actually largest in the first case. The same... 

The hydrogen bond formation has also an influence on the acidities of, for example, the above-mentioned hydroxybenzoic acids since the proton attraction of the carboxyl group is partially saturated by it and the basicity of the anion is therefore smaller. 

Other examples of ancillary ligands used to enhance analyte selectivity include amide-modified D03A (1,4,7,10-tetraazacyclododecane-l,4,7-trisacetate) complexed to Tb , which selectively binds the bidentate analytes p-dimethylaminobenzoic acid (DMABA) and SA (160-162). The binary complex of with EDTA can effectively detect SA, 4-aminosalicylic acid and 5-fluorosalicylic acid (163). [Tb(EDTA)] also has been used to detect catalysis of hydroxybenzoic acid (HBA) by hemin via formation of a ternary complex with the HBA oxidation product (164). Diaza-crown ethers have been utilized with and Eu to detect phthalate, benzoate,... 

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