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any of three aromatic carboxylic acids, CH3C6H4COOH; the closest homologues of benzoic acid. All three toluic acids (the ortho, meta, and para isomers) are colorless crystalline substances that are virtually insoluble in water but are soluble in ethyl alcohol, diethyl ether, and other organic solvents. The three isomers have melting points of 107°, 112°, and 178°C, respectively. Toluic acids may be obtained by the oxidation of xylenes and from toluidines.
The simplest aliphatic-aromatic carboxylic acid—phenylacetic acid, C6H5CH2COOH, which is often called α-toluic acid—is also considered a toluic acid. Phenylacetic acid is a colorless crystalline compound that has limited solubility in water but is readily soluble in organic solvents; its melting point is 76°C. It is obtained by the reaction of benzyl chloride with potassium cyanide, with subsequent hydrolysis of benzylnitrile, C6H5CH2CN, using dilute sulfuric acid, α-toluic acid is used as a raw material in the production of the drug phenocoll and as an additive to the nutrient medium in the cultivation of mold in the production of benzylpenicillin. Esters of α-toluic acid—for example, the ethyl ester—are odoriferous substances.
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