Phenolcarboxylic acids

Phenolat, n. phenoxide, phenolate. Phenol-ather, m. phenol ether, -carbonsaure, /. phenolcarboxylic acid, -gruppe, /, phenol group,... 

Salicylic acid is manufactured on a large scale. In the dye industry it serves for the production of valuable azo-dyes which exhibit great fastness. To some extent these dyes are applied to mordanted fibres. In addition, the acid and its derivatives are widely used in pharmacy. Being a phenolcarboxylic acid it has a powerful disinfecting action (preservative). It has further proved itself an important antirheumatic and an analgetic. The derivative in which the phenolic hydroxyl group is acetylated (aspirin) has become especially popular. The first medicament of the series was the phenyl ester of salicylic acid, salol, which is produced as a by-product in the technical process. The preparation of salicylaldehyde has been described above (p. 235). 

The red salts are the di-alkali salts of the quinonoid phenolcarboxylic acid formulated. This acid is not stable in the free state, but undergoes immediate isomerisation to the colourless lactone. 

Diozo Oxides. Diazo oxides are obtd irom substituted aminophenols amino-naphthols. They are also obtd from amino-phenolcarboxylic acids with the amino group either ortho or para to the hydroxyl group. 

Other experiments show that phenolcarboxylic acids labelled in the carboxyl group form radioactive polymers by simultaneously forming Cl4(>2. This means that not all C1402 is split off, and the polymerization does not occur only through quinones as intermediate steps. Demethylation of the lignin decomposition products is a further important reaction because o-benzoquinones can be formed under certain conditions. 

Color test. Some phenols give characteristic colors on addition of a drop of ferric chloride solution to a dilute aqueous or alcoholic solution of the material. The test is negative with nitrophenols and with m- and p-phenolcarboxylic acids. The j8-keto ester (1) and the j8-diketone (2) give ferric chloride color tests indicative of the presence of the enol forms. 

The hRf values under short-wavelength UV light are determined from the fluo-recence-quenching zones (flavonoids and phenolcarboxylic acids) on a pale green, fluoescent background. 

Potassium carbonate Kolbe synthesis of phenolcarboxylic acids from phenols KaCO,... 

The TLC plate is sprayed with freshly prepared solution and inspected in UV-363nni. The flavonoid glycosides and phenolcarboxylic acids (Aurantii pericarpium, Cynarae herba) show an orange, green or blue to blue-green fluorescence in UV-365 nm. 

A characteristically high amount of rutin, chlorogenic acid and traces of other flavonoid glycosides (R, — 0.1/0.65) represent the flavonoid phenolcarboxylic acid pattern of methanolic extract (2). 

The hydrolysable ones have a structure of polyesters with two essential constituents — saccharide and phenolcarboxylic acid. Under the effect of hydrolytic agents (acids, enzymes, alkalies) they split into the original components. Thus, gallotannines provide — in addition to the sucrose component — also gallic acid, and elagitannines provide hexahydroxydiphenyl... 

CgHgOi, Mr 168.15, needles, mp. 176 °C (anhydrous), 186-189 °C (monohydrate), soluble in water and alcohol. The phenolcarboxylic acid O. represents an important intermediate in the biosynthesis of aromatic natural products from polyketides. 

Acetate/malonate Fatty acid derivatives (n-alkanes, acetylene derivatives). Polyketides (anthracene derivatives, tetracyclines, griseofulvin, phenolcarboxylic acids from fungi and lichens, pyridine derivatives). 

Phenylpropane amino acids Cinnamic acid, coumarins, lignin, lignans, flavan derivatives, stilbenes, phenolcarboxylic acids, phenols, components of volatile oils. 

Since the lower phenols are volatile, they are best separated after conversion into involatile, coloured derivatives (azo dyes) (see p. 664) [37, 87, 154]. The TLC of the azo compounds derived from other simple alkyl phenols also has been described in these articles [37, 87]. Eaesel-guhr layers, impregnated with formamide, have been used as well as strongly alkaline silica gel layers. After separation, the coloured derivatives can be quantitatively eluted from the layer and determined [154]. Mixtures of alcohols and phenols can be satisfactorily chromatographed as their dinitrobenzoates [38]. Numerous phenolcarboxylic acids have been separated on mixed layers of silica gel G and cellulose, using the solvents toluene-ethyl formate-formic acid (50 + 40 + 10) and chloroform-acetic acid-water (80 + 20 + 20). Phenolcarboxylic acids differing little in polarity, can be better separated if the layers are saturated with moisture before use [158]. 

Table 164. Group B, substances of medium polarity Phenols, phenolcarboxylic acids, hydroxycoumarins, flavone aglycones. Comparison of the h /-values obtained under standard conditions on ceUulose, silica gel and...

V Toluene-ethyl formate-formic acid (50 + 40 + 10) B Phenols, flavone aglycones, phenolcarboxylic acids, hydroxycoumarins [203]... 

TLC-fingerprint analysis of Flavonoids, Coumarins and Phenolcarboxylic acids... 

Stankova N V, Smirnova T A 1975 Phenolcarboxylic acids of grape roots. Khim Prir Soedin 22 508-509... 

Table 7.2.5. Formal relationships between gallic acid and some naturally occurring phenolcarboxylic acids...

Number of gallic acid molecules Formal chemical relationship Phenolcarboxylic acid Hydrolysis products of esters Reference(s)... 

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