Benzoic acid and benzoates

Benzoic acid occurs naturally in some fruits and vegetables, notably in cranberries, where it occurs in amounts of the order of 0.08% m/m (Fellows Esselen, 1955). It is also found in some resins, chiefly in gum benzoin (from Styrax ben-zoia), and in coal tar. Commercially available benzoic acid is produced by chemical synthesis. 

Pure benzoic acid is a white powdery crystalline solid (m.p. 122°C) only sparingly soluble in water at normal temperatures. Because of this, it is added to the drink in the soluble form of its sodium or potassium salts. It is normal practice to disperse the benzoate completely during batch makeup before addition of the acid component, with its resulting pH reduction, to avoid localised precipitation of the free benzoic acid due to its solubility having been exceeded (the solubility of benzoic acid = 0.35% m/v at 20°C). It is the free or undissociated form of benzoic acid that exhibits preservative action and hence its use is only effective when low pH values are encountered, ideally below pH 3, at which point the degree of dissociation reduces to below 10%. 

Benzoic acid is generally considered to exhibit an inhibitory effect on microbial growth, although it is of little use for bacterial control, where the greatest problem will occur at pH values above 4, outside the effective limit mentioned above. Improved results are obtained when it is used in conjunction with other preservatives, for example, S02 or sorbic acid, due to synergistic effects. It is interesting to note that the current European Directive, which sets individual limits of 300 rng/1 for sorbic acid and 150 mg/1 for benzoic acid in non-alcoholic flavoured drinks, nevertheless permits a joint preservative use of up to 250 mg/1 sorbic acid with 150 mg/1 benzoic acid. 

Allergic responses to benzoic acid have been reported, particularly among children known to be made hyperactive by other agents, for example, tartrazine. The maximum ADI for benzoic acid, recommended by JECFA, is 5 mg/kg body weight. 

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The equilibrium constant for the proton transfer reaction of benzoic acid, determined in Example, is 6.4 X 10. Calculate the equilibrium concentration of benzoic acid and benzoate anions in a 5.0 X 10 M aqueous solution of the acid. 

Adogen has been shown to be an excellent phase-transfer catalyst for the per-carbonate oxidation of alcohols to the corresponding carbonyl compounds [1]. Generally, unsaturated alcohols are oxidized more readily than the saturated alcohols. The reaction is more effective when a catalytic amount of potassium dichromate is also added to the reaction mixture [ 1 ] comparable results have been obtained by the addition of catalytic amounts of pyridinium dichromate [2], The course of the corresponding oxidation of a-substituted benzylic alcohols is controlled by the nature of the a-substituent and the organic solvent. In addition to the expected ketones, cleavage of the a-substituent can occur with the formation of benzaldehyde, benzoic acid and benzoate esters. The cleavage products predominate when acetonitrile is used as the solvent [3]. 

More detailed information on the reaction course of the three-step functionalization of an HHPA polyesteramide resin was obtained by functionalization with benzoic acid, after the polycondensation step. The reaction proceedings were monitored by multiple detector GPC (UV/RI) and titration. In the UV detector of the GPC the absorption of the aromatic acid is very dominant over the ahphatic resin itself, so that differentiation between free benzoic acid and benzoate-functionalized resin is feasible. It was observed that the titrated total acid concentration decreased much slower than the amount of free benzoic acid (Fig. 11). 

In addition to benzene and alkylbenzenes several other aromatics (nitrobenzene, aniline, anisole, benzoic acid, etc.) were hydrogenated, usually with much lower rates. Benzoic acid and benzoates gave the corresponding cyclohexyl derivatives, however, in case of acetophenone some deoxygenation was also observed with the Ru-3 catalyst [158]. This latter observation raises some doubts regarding the truly homogeneous nature of the reaction. 

Soda lime Benzoic acid and benzoates, when heated in an ignition tube with excess soda lime, are decomposed into benzene, C6H6, which bums with a smoky flame, and carbon dioxide, the latter combining with the alkali present. 

Terephthalic acid is a useful source material of PET, as well as benzoic acid and benzoates. However, in order to recycle the terephthalic acid, produced further purification is required, because other organic compounds are also produced as impurities in the degradation process of waste plastic mixtures, e.g. PE and PET mixtures described in Section 2.3. 

Advantageously, the Smuda Process can tolerate high levels of PET. In catalytic pyrolysis the terephthalic acid is decarboxylated to give benzoic acid and benzoates [24] (see also Figure 15.3). PET gives fuel with appreciable aromatic content (e.g. level of 10% or higher). In other competitive processes PET proves problematic due to the formation of troublesome terephthalic acid (TPA) deposits in the downstream pipework and condensors. 

Benzoic acid and benzoates It may increase the risk of jaundice in newborn babies... 

The range of chemical analyses carried out to determine compliance with quality and specification requirements can include pH, titratable, and volatile acidity total solids, soluble solids (°Brix), water-in-soluble solids, sugars acid-insoluble ash, alkalinity of ash, mineral impurities, trace metals (tin, copper, zinc, iron, aluminum), heavy metals, e.g., lead ethanol preservatives such as sulfur dioxide, sorbic acid, benzoic acid, and benzoates. 

Rosene and Manes studied the effect of pH on the total adsorption from aqueous solutions of sodium benzoate + benzoic acid by activated charcoal. They interpreted their data in terms of the Polanyi potential theory applied to bisolute adsorption (see later p. 117), in which the concentrations of neutral benzoic acid and benzoate anions depend on the pH of the solution (activity coefficient corrections were ignored). They confirmed that, at constant total equilibrium concentration, the adsorption dropped from a relatively high plateau for pH <2 down to a small adsorption at pH >10. The analysis of results is somewhat more complex than with essentially non-electrolyte adsorption, and in this case there were additional effects involving chemisorption of benzoate ion by residual ash in the carbon which had, therefore, to be eliminated. Even with ash-extracted carbon there was evidence of some residual chemisorption. The theoretical analysis correlated satisfactorily with the experimental data on the basis that at pH >10 sodium benzoate is not physically adsorbed and that the effect of pH is completely accounted for by its effect on the concentration of free acid. In addition the theory explains successfully the increase in pH (called by the authors hydrolytic adsorption ) when solutions of sodium benzoate are treated with neutral carbon. However, no account is taken in this paper of the effect of pH on the surface charge of the carbon. 

Determination of Sorbic Acid and Sorbates, Benzoic Acid, and Benzoates... 

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