AMIDE (am'id; from ammonia, + ide), in chemistry, a general name for a class of bodies which may be regarded as derived from am monia, NH,, by replacing one or more of the hydrogen atoms in that substance by an equal number of monovalent acid radicals. Thus formic acid, H.CO.OH, may be regarded as a hydrate of the acid radical HCO; and the compound HCO.NH,, which is known as formamide,)) and is obtained by the action of ethyl formate upon ammonia, may be regarded as derived from ammonia by the substitution of the radical HCO for one of the hydrogen atoms in NH,. Similarly, acetic acid, CH,.CO. OH, may be regarded as a hydrate of the radi cal ((acetyl" (C,11,0) ; and acetamide, which has the formula C,H2O.NH,, and is produced by the action of ethyl acetate upon ammonia, may be regarded as derived from ammonia by the substitution of the radical for one of the hydrogen atoms in the ammonia.
Taking the general formula of a normal fatty acid as X.CO.OH, where X represents an alcohol radical (see ALcouot), an amide may be formed by substituting the monovalent acid radical, XCO, for one of the hydrogen atoms in The resulting substance, XCO.NH,, is called the «primary amide" of the acid radi cal XCO. By the further substitution of XCO for one of the atoms of hydrogen remaining in the primary amide, a ((secondary amide" of the same acid radical is obtained, having the formula (XCO),.NH. It is evident that a amide," having the formula (XCO),N, is also possible.
For some purposes it is convenient to regard the primary amide, XCO.NH, of the monobasic acid X.CO.OH, from the opposite point of view; namely, as derived from the acid by the substitution of the radical NH, for the hy droxyl group OH. Obviously the result is the same in either case; but this latter view makes the deportment of dibasic acid radicals easier to describe. Thus in the dibasic acid Y (CO.
OH), (where Y is a divalent radical), the first result of the substitution of NH, for OH is the formation of the body Y(CO.OH).(CO. NH:), which is both an acid and an amide— an amide because it is obtained by the substitu tion of NH, for OH, and an acid because it still contains one molecule of hydrogen that is replaceable by a monovalent metal or radical (namely, the molecule of H in the OH). Bodies of this type are called aamic acids? If the molecule of OH remaining in an amic acid is replaced by a further substitution of NH,, the resulting substance, Y(CO.NI-1,),, is called a °di-amide," and may be regarded as formed from two molecules of ammonia by the substitution of the divalent acid radical Y(C0), for one-third of the total hydrogen present in those molecules.
The chemistry of the amides is very in volved. They are mostly solid bodies, neutral to litmus, but capable of forming compounds with acids. The amides may be formed in sev eral ways: (1) By the action of ammonia on ethers; (2) by the action of ammonia on acid chlorides; (3) by the dehydration of ammo nium salts; (4) by the action of ammonia on anhydrides; (5) from nitrites and cold concen trated hydrochloric acid; (6) by heating acids with ammonium sulphocyanide for several days. The most familiar example of the class is the primary amide of acetyl or ((acetamide." This substance, which is usually obtained by the dry distillation of acetate of ammonium at temperatures exceeding 375° F., has the for mula C,H2O.NH,, as noted above, and forms hexagonal crystals. It melts at about 180° F., boils at about and is quite soluble in water. Diacetamide, (C,H2O),.NH, and triacetamide, (C,}1,0)..N, are also known. See AMINE;