Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/583

Rh ORGANIC ACIDS.] CHEMISTRY 571 formulas Isomer- dibasic acids, two series of salts, normal and acid, of the COOH and C H I COOM COOM ai &quot; tl 2 COOM ides of many of the acids are known. Oxalates may be formed from cyanogen compounds (see p. 554). Series C n H 2n _ 1 (HO)(C0 2 H) 2, Malic Series: Tartronic or oxymalonic acid CH(HO)(C0 2 H) 2 Malic or oxysuccinic acid C 2 H 3 (HO)(C0 2 H) 2 Citramalic and glutanic acids C 3 H 5 (HO)(C0 2 H), Oxyadipic acid C 4 H 7 (HO)(C0 2 H) 2 Oxysuberic acid C 6 H n (HO)(C0 2 H) 2 Malic acid is found free or combined in the juice of most fruits. Series C, i H 2rt _ 2 (HO) 2 (C0 2 H) 2, Tartaric Series. The fol lowing are known : Mesoxalic acid (?) C(HO) 2 (C0 2 H) 2 Tartaric acid C 2 H 2 (HO) 2 (C0 2 H) 2 Homo-, citra-, and ita-tartaric acids... C 3 H 4 (HO) 2 (C0 2 H). 2 Dioxyadipic acid C 4 H 6 (HO) 2 (C0 2 H) 2 Dioxysuberic C 6 H 10 (HO) 2 (C0 2 H) 2 Tartaric, like malic and oxalic acids, is of frequent occur rence in the vegetable kingdom, being found free or com bined in the juice of many fruits. It is generally obtained from argol or tartar (crude acid potassium tartrate), which is deposited from fermenting grape juice. It can be formed by the action of Ag 2 O and water on dibromsuccinic acid, C 2 H 2 Br 2 (C0 2 H) 2. Five modifications of tartaric acid, differing chiefly in their optical properties, are known, viz., dextrotartaric, levotartaric, racemic, mesotartaric, and meta- tartaric acids. Normal and acid tartrates are known. Tartar emetic is potassio-antimonious tartrate; the acid potassium tartrate is known as cream of tartar. Series C, l H 2n _ 2 (C0 2 H) 2&amp;gt; ^mar^c Series. This consists of fumaric and maleic acids, C 2 H 2 (C0 2 H) 2 ; citraconic, itaconic, and mesaconic acids, C 3 H 4 (C0 2 H) 2. Series C n H 2n _ 8 (C0 2 H) 2, Phthalic Series, comprises : Phthalic (ortho-), isophthalic (meta-), and tere- phthalic (para-) acids Uvitic or mesidic, xylidic, and isoxylidic acids C 7 H 6 (C0 2 H) 2 Cumidic acid C 8 H 8 (C0 2 H) 2 The phthalic acids are obtained by the oxidation of many aromatic hydrocarbons and their derivatives. De rived from these acids are hydro-phthalic and hydrotere- phthalic acids (C 8 H 8 O 4 ). Tribasic Acids. Meconic acid, C 4 HO(C0 2 H) 3, is obtained from opium ; tricarballylic acid, C 3 H 5 (C0 2 H) 3, from tricyanopropane (see p. 568). Citric acid, C 3 H 4 (HO) (C0 2 H) 3, exists in many fruits, and is generally obtained from lemon juice. It forms colourless crystals readily soluble in water. Being a tribasic acid, it forms with metals three classes of salts, typified by M C 6 H 7 O 7, M 2 C 6 H 6 7 , M 3 C 6 H 5 O 7 , &c. Aconitic acid, C 3 H 3 (C0 2 H) 3, is derived from citric acid, and is found also in rnonkshood (Aconitum Napellus}. Trimellitic (para-}, trimesic (meta-}, and hemimellitic (ortho-} acids, C 6 H 3 (C0 2 H) 3, are tricarboxyl derivatives of benzene. Tetrabasic and Hexabasic Acids. The following tetracarboxyl benzene derivatives are known : pyromellitic (para-}, prehnitic (meta-}, and mello- phanic (ortho-} acids, C 6 H 2 (C0 2 H) 4 . The hexabasic acids known are mellitic acid, C 6 (C0 2 H) 6, and its derivative hydromellitic acid, C 6 H 6 (C0 2 H) 6 . It is to be remembered that the foregoing list is neces sarily brief. Many acids of vegetable and animal origin, and others derived from them by artificial methods, are known, but their constitution is in many cases still undecided. IX. ANHYDRIDES. These compounds are the ethers of acid radicles (see p. 553), and may be prepared in many cases by analogous reactions : C 2 H 3 O.C1 + C 2 H 3 O.ONa = (C 2 H 3 O) 2 O + NaCl Acetyl chloride. Sodium acetate. Acetic anhydride. C 2 H 3 O.C1 + C 4 H 7 O.ONa = C 2 H 3 O.O.C 4 H 7 + NaCl. Acetyl chloride. Sodium butyrate. Aceto-butyric anhydride. Many anhydrides are obtained by heating the correspond ing acids : (C 3 H 4 0)&quot;(HO) 2 - OH 2 - (C 3 H 4 0)&quot;O Lactic acid. Lactic anhydride (lactide). (C 8 H 4 2 )&quot;(HO) 2 - OH 2 = (C 8 H 4 2 )&quot;0. Phthalic acid. Phthalic anhydride. Anhydrides when acted on by water yield the corre sponding acids : (C 2 H 3 0) 2 + OH 2 = 2(C 2 H 3 0)HO C 2 H 3 O.O.C 4 H 7 + OH 2 = (C 2 H 3 O)HO + (C 4 H 7 0)HO . Aceto-butyric anhydride. Acetic acid. Butyric acid. Compound anhydrides when distilled are resolved into two simple anhydrides 2C 2 H 3 O.O.C 7 H 5 = (C 2 H 3 0) 2 O + (C 7 H 5 0) 2 O. Aceto-benzoic anhydride. Acetic anhydride. Benzole anhydride. Acetic anhydride is an oily liquid, boiling at 137, and having a pungent odour. By the action of P 2 S 5 it yields thiacetic anhydride, (C 2 H 3 0) 2 S, and by Ba0 2 acetic per oxide, (C 2 H 3 O) 2 2. It combines directly with aldehydes. X. ACID HALIDES. These may be regarded as the haloid ethers of acid radicles. They can be prepared by the action of haloid phosphorus compounds on the acids containing the corre sponding radicles 3(C 2 H 3 O)HO + PC1 3 = 3C 2 H 3 O.C1 + PH 3 O 3 Acetic acid. Acetyl chloride. (C 4 H 4 2 )&quot;(HO) Succinic acid. A similar reaction can be effected with the haloid sub stitution compounds of the acids. Thus, C 2 H 2 C10.C1, C 2 HC1 2 O.C1, and C 2 C1 3 O.C1 (mono-, di-, and tri-chlor- acetyl chlorides) can be obtained by the action of PCJ 3 on mono-, di-, and tri-chloracetic acids. The compounds of this family must be distinguished from the haloid salts of the acids which contain the halogen atom in the place of the carboxyl hydrogen ; for instance O O 2 1- 2PC1 5 = (C 4 H 4 2 )&quot;C1 2 + 2POC1 3 Succinyl chloride. 2HC1 H 3 C C Cl Acetyl chloride. H 3 C C OC1 Chlorine acetate. The latter compound is a yellow liquid produced by the action of acetic anhydride upon hypochlorous anhydride : (C 2 H 3 O) 2 + C1 2 O = 2C 2 H 3 O. OC1. It is very unstable, being decomposed by heat, Br, I, and most metals. The corresponding iodine compound produced by the action of iodine on the chlorine acetate is interesting as showing the triad nature of the iodine atom [(C 2 H 3 0)O] 3 I&quot;. The acid halides are as a rule colourless liquids more or less oily, and possessing characteristic odours. They are decomposed by water : C 2 H 3 O.C1 + OH 2 = (C 2 H 3 0)HO + HC1 Acetyl chloride. Acetic acid. C 7 H 5 O.C1 + OH 2 = (C 7 H 5 0)HO + HC1. Benzoyl chloride. Benzoic acid. In some cases the whole of the halogen is not removed by the action of cold water : (C 3 H 4 0)&quot;C1 2 Lactyl dichloride. OH 2 = (C 3 H 4 C10)HO + HC1. Chloropropionic acid.