(1341) Amidated Acids.-If, instead of operating upon a normal ammonium salt obtained from either a monobasic or a dibasic acid, any of the acid salts formed by ammonium with the dibasic acids be subjected to dehydration, a body is produced belonging to the class of amidic, or amidated acids. Balard, in distilling the acid ammonium oxalate, thus obtained an azotised acid, which has been termed oxamic acid : This substance may serve as the type of a numerous class of compound acids, formed in a similar manner. The ammonium loses hydrogen, and the portion of the acid attached to the ammonium of the original salt loses oxygen, whilst that portion of acid which was attached to basic hydrogen remains unaltered ; so that oxamic acid may be viewed as a compound of unchanged oxalic acid and of oxamide : The amidic acids may also be obtained by acting upon the anhydride of a dibasic acid (1270) with dry ammonia in excess : the two bodies combine together, but the compound which is produced is found on examination to give evidence of the presence of but one half of the ammonia in the form of an ordinary ammonium salt; the second half having united with the elements of the acid to produce a new compound acid, which is the amidated. acid of the one originally employed (Laurent). For instance, I molecule of camphoric anhydride when acted upon by 1 of ammonia, yields 1 of camphoramic acid; the decomposition being supposed to consist in the conversion of one half of the molecule of camphoric anhydride into camphoramide, while water is given off and enters into combination with the other half of the acid; these two bodies, camphoramide and camphoric acid then unite and form the new acid : 468 AMIDIC ACIDS-IMIDES. This amidic acid may be converted into ammonium camphoramate by causing it to unite with a second atom of ammonia. The amidic acids may therefore be viewed as monobasic compounds derived from dibasic acids, in which one half of the group composing the original dibasic acid is displaced by one half of the group which forms the amide of the acid; the combination of 1 molecule of the original dibasic acid with 1 of the amide furnishing 2 molecules of the monobasic amidic acid. To take again the case of the camphoric acid: Camphoric acid. Camphoramide. Camphoramic acid. HọCH,O + (H,N),H,O = 2 (H,H,N,C,H,O,). 101 14 4 14 2 2 10 14 When the aqueous solutions of the amidic acids are boiled, they quickly unite with the elements of water, and become reconverted into acid ammonium salts. Hofmann regards the amidic acids as bodies formed upon the type of hydrated ammonium oxide, a substance too unstable to exist by itself, but acquiring permanence when two atoms of its hydrogen have been displaced by the radicle of a dibasic acid. Thus we may compare oxamic acid with hydrated ammonium oxide : The action of nitrous anhydride (N,,) upon the amidated acids is characteristic: mutual decomposition occurs, nitrogen and water are liberated, and the original acid from which the amidated compound was derived is reproduced. Aspartic acid (1317), for example, may thus be reconverted into malic acid : (1342) Imides.-Intermediate between the amides and the nitriles there is a third class of bodies, the imides, which contain nitrogen, and in which, if we are consistent, the existence of a body termed imidogen HN (or ammonia less two atoms of hydrogen), must be assumed to exist. These compounds are not numerous, but several of them are well known. They are obtained by a process of dehydration from certain acid ammonium salts, and from the amidated acids procurable from these salts; succinic, camphoric, and phthalic acids, for instance, each yield. VARIETIES OF AMIDES. 469 imidic compounds. The relation of these bodies to their re spective acids will be seen by the following comparison : Acid ammonium camphorate 10 Camphoramic acid (amidated camphoric acid) HH,N, H. Camphorimide Phthalic acid 10 14 Hence it will be perceived, that the imides are bodies formed from the amidic acids by depriving the molecule of these compounds of one atom of water, just as the amidic acids are themselves obtained from the acid ammonium salts by depriving the molecule of the latter of an atom of water : The theory of the existence of amidogen and imidogen as distinct organic groups or radicles in these different bodies, does not, upon a general view of the question, appear to have any strong probability. It was, indeed, proposed merely as a temporary expedient for representing the facts. The different groups designated as amides, imides, and nitriles, must rather be regarded as residues, the results of successive stages of dehydration. The terms themselves may, however, be conveniently retained, provided that their use be not taken to imply an adhesion to the theory in accordance with which these names were framed. We may sum up the foregoing facts in the following manner. The compounds which correspond to the normal ammonium salts are: 1. The amides, produced by the combination of I molecule of the normal monobasic acid with 1 of ammonia, and the elimination of one atom of water. 2. The diumides, produced by the combination of 1 molecule of the normal dibasic acid with 2 molecules of ammonia, attended by the separation of two atoms of water. 3. The nitriles, produced by a combination of 1 molecule of a normal monobasic acid and 1 of ammonia, minus 2 H2O; or from 1 molecule of a normal dibasic acid and 2 molecules of ammonia, minus 4 H2O. 470 HYDRAMIDES-THEORY OF THE AMIDES. The compounds which correspond to the acid ammonium salts are: 4. Amidic acids, formed from 1 molecule of a normal dibasic acid and I of ammonia, minus H2O. 5. Imides, formed from 1 molecule of a normal dibasic acid and one of ammonia, with elimination of 2 H2O. (1343) Hydramides.-Besides the varieties of amides already mentioned, a particular class of compounds is formed by the action of ammonia upon certain volatile oils which are indeed the aldehyds of the aromatic acids. These bodies, termed hydramides, are furnished by the union of 3 molecules of the volatile oil and 2 molecules of ammonia, while water is separated in the proportion of 3 H,O. Compounds of this kind are formed with the essential oils of bitter almonds, of spiræa, of cinnamon, of cumin, and of anise, as for example : 2 Benzoyl hydride. Hydrobenzamide. 3 (Є,H,,H) + 2 H2N – 3 H2O = €21H1N2. 5 Salicyl hydride. 182* Salbydramide. Sulphuretted hydrogen, in acting upon the hydramides, removes the elements of ammonia, and converts them into bodies analogous to the essences from which they were originally obtained, but the new essences contain as many atoms of sulphur as they previously possessed of oxygen; for example, thiobenzol is obtained from hydrobenzamide, and thiosalicol from salhydramide Hydrobenzamide. Thiobenzol. €21H18N + 3 H2S = 2 H2N + 3 (¤,H¿S‚H); (1344) Theory of the Amides.-The amides, ever since their discovery, have offered interesting subjects of investigation and speculation to the chemist. They are substances which, although derived from ammonia, generally exhibit no basic power, and yet in certain cases they can be converted into compounds which possess all the properties of powerful alkalies. Although this subject is somewhat abstruse, we shall enter into it in some detail, THEORY OF THE AMIDES. 471 in order to furnish some idea of the number and variety of the products which may be obtained by the methods of substitution from a body apparently so simple as ammonia, as well as to exemplify the great variety of methods in which it is possible and even necessary to pursue researches of this description. The researches of Gerhardt and Chiozza (Ann. de Chimie, III. xlvi. 129) have shown that the amides bear the same relation to their respective acids, that the volatile alkalies, methylia, ethylia, &c., do to the alcohols from which they are formed. The amides, when treated with nitrous anhydride, yield nitrogen and the acid from which the amide was obtained; and, under similar treatment, the volatile alkalies of the aromatic alcohols yield nitrogen and their corresponding alcohol.* Upon this view, therefore, the amides are compounds derived by substitution from ammonia, upon which as a type they are founded; the ordinary amides of the monobasic acids, such as benzamide, being ammonia in which the basic character is neutralized by the substitution of an electro-negative radicle (such as benzoyl) for one of its atoms of hydrogen: for instance, H ammonia being HN, H benzamide would be H N; and starting from this idea, Gerhardt was led to effect upon the amides a series of substitutions similar to those performed by Hofmann with ethylia and its homologues. In this manner he was enabled by double decomposition to obtain amides, in which one atom or two atoms of hydrogen were displaced by certain electro-negative bodies; these electro-negative bodies being compounds which when substituted for either one half or both halves of the hydrogen in the atom of water, furnish in one case, the normal acids; in the other, the anhydrides (1268): benzoyl (E,H.), for instance, when thus substituted successively for hydrogen, yields first benzoic acid, then benzoic anhydride : |