Benzoic acid, p-hydroxy

When the phenol contains a carboxylic acid group, e.g., m- or p-hydroxy-benzoic acid, the acetylated derivative will of course remain in solution as the sodium salt, but is precipitated when the solution is subsequently acidified. Salicylic acid, however, cannot be acetylated under these conditions. 

In a variation of the scheme above, alkylation of p-hydroxy-benzoic acid with cyclohexyl iodide affords the cyclohexyl ether, 55. (Under alkaline reaction conditions, the ester formed concurrently does not survive the reaction.) Acylation of the acid chloride obtained from 55 with the preformed side chain (56) gives cyclomethycaine (57). ... 

Ph-HQ/HQ/BB (50/50) is a crystalline polyarylate and its HDT is 297 °C. We found that copolymerization involving small amounts of the third unit (HBA) into this system could improve its crystallinity (Figure 19.13) and HDT finally, the HDT of the copolyarylate Ph - HQ/HQ/BB/p-hydroxy benzoic acid (HBA) (47.5/47.5/5) increased to above 300 °C. 

The opposite can be observed with acidic analytes as shown in Figure 2.18. Here, with classical RP and methanol at pH 3 the best selectivity and peak shapes were observed. On the other hand, with the shielded phases, acetonitrile gives the best separation. As already discussed, with shield phases the retention of nonpolar components (here peak 6 dimethyl phthalate) is reduced, whereas that of phenolic components (e.g., peak 5 p-hydroxy benzoic acid methyl ester) is increased. 

Problam 16.14 Although p-hydroxy benzoic acid is less acidic than benzoic acid, salicyclic (o-hydroxybenzoic) acid (X, = 105 x 10 ) is 15 times more acidic than benzoic acid. Explain. M... 

Fig. 3.3. Separation of neutral, acidic and basic components in their ionised form with Hypersil unbonded BDS silica. Peak identities 1= Benzylamine, 11= Caffeine and 111= p-hydroxy benzoic acid. The arrow denotes the EOF. Conditions= 6 2 2 v/v/v ACN H2O 50 mM MES, pH 6.1, 20 kV, 20°C, 214 nm, 8 bar for 15 sec. inj. Adaptation of [20]. Reproduced with the permission of Chromatographia.

In accordance with this prediction, Euerby et al. observed a slow EOF at pH 2.5 while separating a mixture of bumetanide, flurbiprophen, and p-hydroxy-benzoic acid using a 3-pm CEC Hypersil C18-packed capillary [40], The running time was 13 min and efficiencies varied from 97,000 to 174,000. 

New Orthoform m-Amine p-hydroxy benzoic acid, methyl ester... 

Ethylparaben is prepared by the esterification of p-hydroxy-benzoic acid with ethanol (95%). 

Phenolic acids include the benzoic acids (Ce-Ci), e.g., gallic, vanillic, syringic, protocatechuic, p-hydroxy-benzoic acid, as well as cinnamic acids (C6-C3), e.g., caffeic, p-coumaric, ferulic, sinapic acids, and their dep-sides and derivates, e.g., rosmarinic acid and lithospermic acid (Fig. 1). Phenolic acids and flavonoids in plants may occur in the free form, but they are often glycosylated with various sugars, especially glucose. Phenolic acids may also be present in the esterified as well as bound forms. Free phenolic acids are found especially in herbs and spices and, very often, in compounds responsible for antioxidant activity (benzoic and cinnamic acids and some of their derivatives). The bound forms are more common for the fruits, vegetables, and other plant materials. Therefore, in some cases, it is necessary to combine the analysis of their free and bound forms. 

An easier method of production of p-anisic acid is methy-lation of p-hydroxy benzoic acid obtained as a co-product during manufacture of o-hydroxy benzoic acid (salicylic acid) via Kolbe reaction of phenol and CO2... 

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