Hydroxy Acids

HYDROXY ACIDS (alcohol acids), compounds of double function, simultaneously alcohols and acids, containing both a hydroxyl group and a carboxyl group. Depending on the position of the OH relative to the COOH (adjacent, one, two, three places away), one distinguishes alpha-, beta-, gamma-, and delta-hydroxy acids. There are many methods for obtaining hydroxy acids; the most important of which are the careful oxidation of glycols: CH₃.CH(ON).CH₂.OH + O₂ = CH₃. .CH(ON).COOH; saponification of oxynitriles CH₃.CH(ON).CN -* CH₃.CH(ON).COOH; exchange of halogen in halogen acids for OH: CH₂Cl.COON + KOH = CH₂(OH).COON + + KCl, the action of HNO₂ on amino acids: CH₂(NH₂). COON + HNO₂ = CH₂(OH) + N₂ + + H₂O. In the animal organism hydroxy acids are formed during deamination (see) of amino acids, during oxidation of fatty acids (see Acetone bodies, Protein metabolism), during glycolysis (see), fermentation (see), and other chemical processes. Hydroxy acids are viscous liquids or crystalline substances. In chemical relation hydroxy acids react both as alcohols and as acids: they give for example both simple and complex esters; under the action of halogen compounds of phosphorus both OH are replaced by halogen; hydrohalogen acids react only with the alcoholic OH. Special reactions characterize alpha-, beta-, gamma-, and delta-hydroxy acids: alpha-hydroxy acids, losing water from two molecules, give cyclic complex esters, lactides: 2CH₂(OH).COON = 2H₂O + CH₂.O.CO (glycolide); gamma- and delta-hydroxy acids form anhydrides - lactones: CH₃.CH(ON).CH₂.CH₂.COON = =H₂O+CH₃.CH.CH₂.CH₂.COO. Hydroxy acids are widely distributed in animal and plant organisms. Representatives of aliphatic alpha-hydroxy acids are glycolic acid, CH₂OH.COOH (oxyacetic acid), lactic acid; from beta-hydroxy acids - hydroacrylic acid, CH₂OH.CH₂COON, beta-hydroxybutyric acid; gamma-hydroxy acids are unknown in the free state, since losing water they pass into lactones. Among dibasic hydroxy acids the important one is malic acid (oxy-succinic acid); COOH.CHOH.CH₂.COON, widely distributed in plants; possesses left rotation in weak solutions, right in strong ones; synthetic acid is inactive. To dibasic four-atom acids belong tartaric acids (di-oxy-succinic acids). From other hydroxy acids - citric acid, HO.CO.CH₂. .(COH)(COON).CH₂.COON, very widespread in the plant world (in grapes, lemons) and found in the animal organism (in milk); in the form of citric iron it has application in medicine. From aromatic hydroxy acids (phenol acids) in medicine have significance salicylic acid, gallic acid and their derivatives; phenyl ether of salicylic acid (salol), sulfosalicylic acid, C₆H₃.OH.S0₃H.COOH (protein reagent), acetylsalicylic acid (aspirin). In plants many different hydroxy acids of the aromatic series occur, to derivatives of which among other things belong tanning substances, having important technical significance. On the biological significance of individual hydroxy acids and on methods of their quantitative determination - see Acetone bodies, Bro-Glycolysis, Deamination, Blood, Lactic Acid, Urine, Muscles, Beta-hydroxybutyric acid.

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