ethide; (4) the synthesis of aromatic acids by the interaction of carbon dioxide, sodium and a bromine substitution derivative; and (5) the synthesis of aromatic oxy-acids by the interaction of carbon dioxide and sodium phenolates (see Salicylic Acid). (Carbon monoxide takes part in the syntheses of sodium formate from sodium hydrate, or soda lime (at 200°–220°), and of sodium acetate and propionate from sodium methylate and sodium ethylate at 160°–220°. Other reactions which introduce carboxyl groups into aromatic groups are: the action of carbonyl chloride on aromatic hydrocarbons in the presence of aluminium chloride, acid-chlorides being formed which are readily decomposed by water to give the acid; the action of urea chloride Cl·CO·NH2, cyanuric acid (CONH)3, nascent cyanic acid, or carbanile on hydrocarbons in the presence of aluminium chloride, acid-amides being obtained which are readily decomposed to give the acid. An important nucleus-synthetic reaction is the saponification of nitriles, which may be obtained by the interaction of potassium cyanide with a halogen substitution derivative or a sulphonic acid.
Acids frequently result as oxidation products, being almost invariably formed in all cases of energetic oxidation. There are certain reactions, however, in which oxidation can be successfully applied to the synthesis of acids. Thus primary alcohols and aldehydes, both of the aliphatic and aromatic series, readily yield on oxidation acids containing the same number of carbon atoms. These reactions may be shown thus:—
R·CH2OH → R·CHO → R·CO·OH.
In the case of aromatic aldehydes, acids are also obtained by means of “Cannizzaro’s reaction” (see Benzaldehyde). An important oxidation synthesis of aromatic acids is from hydrocarbons with aliphatic side chains; thus toluene, or methylbenzene, yields benzoic acid, the xylenes, or dimethyl-benzene, yield methyl-benzoic acids and phthalic acids. Ketones, secondary alcohols and tertiary alcohols yield a mixture of acids on oxidation. We may also notice the disruption of unsaturated acids at the double linkage into a mixture of two acids, when fused with potash.
In the preceding instances the carboxyl group has been synthesized or introduced into a molecule; we have now to consider syntheses from substances already containing carboxyl groups. Of foremost importance are the reactions termed the malonic acid and the aceto-acetic ester syntheses; these are discussed under their own headings. The electrosyntheses call for mention here. It is apparent that metallic salts of organic acids would, in aqueous solution, be ionized, the positive ion being the metal, and the negative ion the acid residue. Esters, however, are not ionized. It is therefore apparent that a mixed salt and ester, for example KO2C·CH2·CH2·CO2C2H5, would give only two ions, viz. potassium and the rest of the molecule. If a solution of potassium acetate be electrolysed the products are ethane, carbon dioxide, potash and hydrogen; in a similar manner, normal potassium succinate gives ethylene, carbon dioxide, potash and hydrogen; these reactions may be represented:—
| CH3·CO2¦ | K CH3 CO2 K• CH2·CO2¦ | K CH2 CO2 K• |
| ¦ | → |++| ¦ | → ‖++ |
| CH3·CO2¦ | K CH3 CO2 K• CH2·CO2¦ | K CH2 CO2 K• |
By electrolysing a solution of potassium ethyl succinate, KO2C·(CH2)2CO2C2H5, the KO2C· groups are split off and the two residues ·(CH2)2CO2C2H5 combine to form the ester (CH2)4(CO2C2H5)2. In the same way, by electrolysing a mixture of a metallic salt and an ester, other nuclei may be condensed; thus potassium acetate and potassium ethyl succinate yield CH3·CH2·CH2·CO2C2H5.
Reactions.—Organic acids yield metallic salts with bases, and ethereal salts or esters (q.v.), R·CO·OR′, with alcohols. Phosphorus chlorides give acid chlorides, R·CO·Cl, the hydroxyl group being replaced by chlorine, and acid anhydrides, (R·CO)2O, a molecule of water being split off between two carboxyl groups. The ammonium salts when heated lose one molecule of water and are converted into acid-amides, R·CO·NH2, which by further dehydration yield nitriles, R·CN. The calcium salts distilled with calcium formate yield aldehydes (q.v.); distilled with soda-lime, ketones (q.v.) result.
ACIDALIUS, VALENS (1567–1595), German scholar and critic, was born at Wittstock in Brandenburg. After studying at Rostock, Greifswald and Helmstedt, and residing about three years in Italy, he settled at Breslau, where he is said to have embraced the Roman Catholic religion. Early in 1595 he accepted an invitation to Neisse, about fifty miles from Breslau, where he died of brain fever on the 25th of May, at the age of twenty-eight. His excessive application to study, and the attacks made upon him in connexion with a pamphlet of which he was reputed the author, doubtless hastened his premature end. Acidalius wrote notes on Velleius Paterculus (1590), Curtius (1594), the panegyrists, Tacitus and Plautus, published after his death.
See Leuschner, Commentatio de A. V. Vita, Moribus, et Scriptis (1757); F. Adam, “Der Neisser Rektor,” in Bericht der Philomathie in Neisse (1872).
ACID-AMIDES, chemical compounds which may be considered as derived from ammonia by replacement of its hydrogen with acidyl residues, the substances produced being known as primary, secondary or tertiary amides, according to the number of hydrogen atoms replaced. Of these compounds, the primary amides of the type R·CO·NH2 are the most important. They may be prepared by the dry distillation of the ammonium salts of the acids (A. W. Hofmann, Ber., 1882, 15, p. 977), by the partial hydrolysis of the nitriles, by the action of ammonia or ammonium carbonate on acid chlorides or anhydrides, or by heating the esters (q.v.) with ammonia. They are solid crystalline compounds (formamide excepted) which are at first soluble in water, the solubility, however, decreasing as the carbon content of the molecule increases. They are easily hydrolysed, breaking up into their components when boiled with acids or alkalies. They form compounds with hydrochloric acid when this gas is passed into their ethereal solution; these compounds, however, are very unstable, being readily decomposed by water. On the other hand, they show faintly acid properties since the hydrogen of the amido group can be replaced by metals to give such compounds as mercury acetamide (CH3CONH)2Hg. Nitrous acid decomposes them, with elimination of nitrogen and the formation of the corresponding acid,
RCO·NH2 + ONOH＝R·COOH + N2 + H2O.
When distilled with phosphoric anhydride they yield nitriles. By the action of bromine and alcoholic potash on the amides, they are converted into amines containing one carbon atom less than the original amide, a reaction which possesses great theoretical importance (A. W. Hofmann),
R·CONH2 → R·CONHBr → R·NH2 + K2CO3 + KBr + H2O.
Formamide, H·CONH2, is a liquid readily soluble in water, boiling at about 195° C. with partial decomposition. Acetamide, CH3·CONH2, is a white deliquescent crystalline solid, which melts at 82–83° C. and boils at 222° C. It is usually prepared by distilling ammonium acetate. It is readily soluble in water and alcohol, but insoluble in ether. Benzamide, C6H5.CONH2, crystallizes in leaflets which melt at 130° C. It is prepared by the action of ammonium carbonate on benzoyl chloride. It yields a silver salt which with ethyl iodide forms benzimidoethyl ether, C6H5C: (NH)·OC2H5, a behaviour which points to the silver salt as being derived from the tautomeric imidobenzoic acid, C6H5C: (NH)·OH (J. Tafel, Ber., 1890, 23, p. 104). On the preparation of the substituted amides from the corresponding sodamides see A. W. Titherley (Journ. Chem. Soc., 1901, 59, p. 391). The secondary and tertiary amides of the types (RCO)2NH and (RCO)3N may be prepared by heating the primary amides or the nitriles with acids or acid anhydrides to 200° C. Thiamides of the type R·CSNH2 are known, and result by the addition of sulphuretted hydrogen to the nitriles, or by the action of phosphorus pentasulphide on the acid-amides. They readily decompose on heating, and are easily hydrolysed by alkalies; they possess a somewhat more acid character than the acid-amides.
ACINACES (from the Greek), an ancient Persian sword, short
