Aromatic hydroxyacids

Table 34 Actinide(IV) Compounds with Aromatic Hydroxyacids...

Tetrabutyl ammonium hydroxide and dimethyl sulfate in dichlo-romethane have been used to methylate a number of aromatic hydroxyacids and hydroxyaldehydes (Ramaswamy et al. 1985). 

In dynamic mechanical and dielectric relaxation studies, Naoki and Akira (26) discovered that the principal relaxation transition in CPE-2 shows a bimodal pattern (Figure 4, curve 3), which, according to (24), may be related to defreezing of local mobility of the two constituent stractural units (i.e., constituents of HBA and HNA). Mobilities of the units of these aromatic hydroxyacids are not very different at 30-90 C, the mobility of HBA units defreezes then, the mobility of HNA units is set fiee at 100-170 C. 

Liquid crystal polyesters are made by a different route. Because they are phenoHc esters, they cannot be made by direct ester exchange between a diphenol and a lower dialkyl ester due to unfavorable reactivities. The usual method is the so-called reverse ester exchange or acidolysis reaction (96) where the phenoHc hydroxyl groups are acylated with a lower aHphatic acid anhydride, eg, acetic or propionic anhydride, and the acetate or propionate ester is heated with an aromatic dicarboxyHc acid, sometimes in the presence of a catalyst. The phenoHc polyester forms readily as the volatile lower acid distills from the reaction mixture. Many Hquid crystal polymers are derived formally from hydroxyacids (97,98) and thein acetates readily undergo self-condensation in the melt, stoichiometric balance being automatically obtained. 

The carboxylic acids can be subdivided into nonvolatile fatty acids, volatile fatty acids, hydroxy acids, dicarboxylic acids, and aromatic acids (Fig. 3). The nonvolatile fatty acids are molecules with more than five carbon atoms, such as stearic and palmitic acids, which are the degradation products of fats and triglycerides. Three different 18-C fatty acids that are important constituents of plants include oleic and linoleic acids that are abundant in plant seeds, and linolenic acid, which is abundant in plant leaves. Volatile fatty acids are short-chain molecules with one to five carbon atoms, such as acetic and valeric acid, associated with anaerobic metabolism. The hydroxy-acids are common intermediates in biochemical pathways, including the tricarboxylic acid cycle. The excretion of hydroxyacids by algae, such as the... 

Conversely, the addition of some other ions can promote solubility by the indifferent electrolyte effect. The use of hydrophilic molecules such as the hydroxyacids (e.g. citrate, tartaric) or aromatic carboxylic acids (e.g. benzoic) can create cavities in the water structure thereby promoting solubilization. Many salt formers increase drug solubility by this type of mechaiusm. Citrate buffers and sodium benzoate, the latter often used in formulations as an antimicrobial preservative, are known to enhance the solubility of a number of drugs. 

The (.S ) -oxynitrilase from Sorghum bicolor produces the other enantiomer but only from aromatic aldehydes.39 The products can be directly converted into hydroxyacids 127 without loss of ee. 

The driving force for the reaction is provided by the formation of a stable carboxy-late salt (potassium benzilate). Once this salt is produced, acidification yields benzilic acid. The reaction can generally be used to convert aromatic a-diketones to aromatic a-hydroxyacids. Other compounds, however, also will undergo benzilic acid-type of rearrangement (see questions). 

Two dye components are needed for dyeing with azo dyes which are synthesised on the fibre a diazonium salt and the coupling compound, abbreviated as the naphthol . Diazonium components are aromatic amines, the fast bases, which must be previously diazotised or stabilised diazonium salts, the fast salts. Coupling components are arylamides of aromatic o-hydroxyacids and of acylacetic acids. Perkavec and Perpar [54] report the TLC-separation of these products. 

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