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Mandelic Acid

MANDELIC ACID (Phenylglycollic Acid), CsHsO, or C 6 H S -CH(OH)-COOH, an isomer of the cresotinic and the oxymethylbenzoic acids. Since the molecule contains an asymmetric carbon atom, the acid exists in three forms, one being an inactive " racemic " mixture, and the other two being optically active forms. The inactive variety is known as paramanddic acid. It may be prepared by the action of hydrochloric acid on the addition compound of benzaldehyde and hydrocyanic acid:

C 6 H 6 CHO+HCN-r-HCH-2H 2 = CeHs-CHOH-COOH+NH^Cl, (F. L. Winckler, Ann., 1836, 18,310), by boiling phenylchloracetic acid with alkalis (A. Spiegel, Ber., 1881, 14, 239), by heating benzpylformaldehyde with alkalis (H. v. Pechmann, Ber., 1887, 20, 2905), and by the action of dilute alkalies on w- dibromacetophenone (C. Engler, Ber., 1887, 20, 2202): CsH 6 COCHBr 2 + 3KHO = 2KBr+ H 2 O + C,H S -CHOH-C0 2 K.

It crystallizes from water in large rhombic crystals, which melt at 118 C. Oxidizing agents convert it into benzaldehyde. When heated with hydriodic acid and phosphorus it forms phenylacetic acid; whilst concentrated hydrobromic acid and hydrochloric acid at moderate temperatures convert it into phenylbrom- and phenylchlor-acetic acids. The inactive mixture may be resolved into its active components by fractional crystallization of the cinchonine salt, when the salt of the dextro modification separates first; or the ammonium salt may be fermented by Penicillium glaucum, when the laevo form is destroyed and the dextro form remains untouched; on the other hand, Saccharomyces ellipsoideus destroys the dextro form, but does not touch the laevo form. A mixture of the two forms in equivalent quantities produces the inactive variety, which is also obtained when either form is heated for some hours to 1 60 C.

Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)

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