AMIDINES  , in organic

chemistry, the name given to compounds of general formula R•C: (NH) . NH2, which maybe considered as derived from the acid-amides by replacement of oxygen by the divalent imino (=NH) group . They may be prepared by the action of ammonia or amines on imide chorides, or on thiamides (O . Wallach, A . Bernthsen); by the action of ammonium chloride or hydrochlorides of amines on nitriles; by condensing amines and amides in presence of phosphorus trichloride; by the action of hydrochloric acid on acid-amides (O . Wallach, Ber., 1882, 15, p . 208); and by the action of ammonia or amines on imino-ethers (A . Pinner, Ber., 1883, 16, p . 1647; 1884, 17,p . 179) . They are monacid bases, which are not very stable; they readily take up the elements of water (when boiled with acids or alkalies) , yielding amides and ammonia . On dry distillation they yield nitriles and ammonia .

When warmed with sulphuretted

hydrogen they yield thiamides, RC : (NH) •NHR+H2S = R C(NH2)(SH)NHR=R•CSNH2+NH2•R or RCS .NHR+ NH3 . With 0-ketonic esters, HO(CH3)C : CH . CO2R, they yield oxypyrimidines (A . Pinner, Ber., 1890, 23, p . 3820) . Formamidine, HC: (NH)NH2, is only known in the form of its salts, the hydrochloride being obtained by the action of ammonia on the hydrochloride of formimido-ethyl ether (A . Pinner, Ber., 1883, 16, p . 3S7) . Acetamidine, CH3C : (NH)•NH2, is alkaline in reaction, and readily splits up into acetic acid and ammonia when warmed with acids . Its hydrochloride melts at 163° C., and crystallizes from alcohol in colourless deliquescent prisms . Acetic anhydride converts the base into an acetamino-dimethyl pyrimidine, acetic acid and acetamide being also formed . Benzamidine, C6H5•C: (NH)NH2, forms colourless crystals which melt at 75—800 C .

When warmed it breaks down into ammonia and cyanphenine (s-triphenyl triazine) . It condenses with acetic anhydride to form a methyldiphenyl triazine, acetamide being also formed; with acetyl-

acetone to form dimethylphenyl pyrimidine (A . Pinner, Ber., 1893, 26, p . 2125); and with trimethylene bromide to form a phenyl tetrahydropyrimidine (Pinner) . H. v . Pechmann (Ber., 1895, 28, p . 2362) has shown that amidines of the type R•C: (NY)•NHZ sometimes react as if they possessed the constitution R•C (NZ) . NHY; but this only appears to occur when Y and Z are groups which function in the same way . If Y and Z are groups which behave very differently, then there is apparently no tautomerism and a definite formula can be given to the compound . The formulae of the ringed compounds mentioned above are here shown: N —C—(CH3) / > CH =C—(OH) Oxypyrimidine . N —C/C6H6 \N NC\CH3 Methyldiphenyl triazine . Phenyl tetrahydropyrimidine .