128 



NA TURE 



[December io, 1891 



most interesting chemical events of last year. The ex- 

 traordinary nature of the compound— manifested by its 

 fearfully explosive properties, together with its acid cha- 

 racter, by virtue of which it forms salts with metals con- 

 taining only metal and nitrogen — mark out for it a place 

 among the most attractive of hitherto discovered sub- 

 stances. It was first obtained by Prof. Curtius in the 

 form of a gas, by treating with soda a compound contain- 

 ing the organic radicle benzoyl in the place of the hydrogen 

 atom, and subsequently warming the sodium salt thus 

 produced with dilute sulphuric acid. The gas was de- 

 scribed as possessing a frightfully penetrating odour, and 

 as being absorbed by water with extreme avidity, forming 

 a solution of strongly acid properties, which liberates 

 hydrogen in contact with metals. So great, indeed, is 

 the afifinity of azoimide for water, that in these earlier 

 •experiments it was not found possible to collect the gas 

 in the anhydrous state. Shortly after the publication of 

 his first communication (see Nature, vol. xlii. p. 613), 

 an improved method of preparing the solution in water 

 was devised by Prof. Curtius. It consisted in distilling 

 a soda solution of a derivative containing the radicle of 

 hippuric acid with dilute sulphuric acid. He was thus 

 enabled to obtain a tolerably large quantity of the aqueous 

 acid. By successive fractionation of this solution in water, 

 and finally distilling the last product of the fractionation 

 over fused calcium chloride, pure azoimide itself was 

 •eventually isolated, and found to be a volatile liquid, 

 boiling at 37°. 



Owing to the terribly explosive nature of both the free 

 acid and its salts, the work has been attended with con- 

 siderable danger, and has, unfortunately, been delayed 

 by a lamentable accident which befell Prof. Curtius's 

 assistant, Dr. Radenhausen, who was seriously injured 

 by the explosion of a quantity of the anhydrous acid. 

 At length, however, Prof. Curtius is able to publish some 

 further particulars concerning the acid and its salts, and 

 an important communication from him will be found in 

 the current number of the Berichte of the German Chem- 

 ical Society. The following is a brief account of these 

 further research?s, together with a resume of the present 

 state of our knowledge of this interesting compound and 

 its derivatives. 



formed, together with benzoate of the alkali. Thus with 

 soda 



CeHjCO— N< I -f 2NaOH = 



CgHgCOONa + NaN< il + H„0. 



When the sodium salt of azoimide is distilled with dilute 

 sulphuric acid, azoimide escapes as a gas, which con- 

 denses along with water in the form of an aqueous 

 solution. 



Hippuric acid reacts with one molecule of hydrazine 

 with formation of hippuryl hydrazine, CeHjCO— NH— 

 CHoCONH— NHo. When this substance is treated with 

 nitrous acid, a compound is obtained which was at first 

 considered to be a nitroso compound, but is how dis- 

 covered to be in reality a diazo compound possessing the 

 constitution CgHsCO— NH— CH.,CONH--N=^N— OH. 

 This substance may be isolated in quantity, and yields 

 salts of azoimide directly upon treatment with alkalies. 

 If soda is employed the sodium salt of azoimide is ob- 

 tained, tfrom which azoimide itself may, as before, be 

 liberated by distilling with dilute sulphuric acid. It is 

 more convenient, however, as will be described later, to 

 employ it directly for the preparation of the ammonium 

 salt of azoimide by saturating its alcoholic solution with 

 ammonia gas ; from the ammonia salt, if desired, 

 azoimide itself may be obtained by converting it into the 

 insoluble silver salt, and distilling the latter with sulphuric 

 acid. 



Preparation and Properties of the Sodium Salt of 

 Azoimide, Na— N<; 



\n 



The method of preparing the sodium salt of azoimide, 

 now adopted as most convenient by Prof. Curtius, is 

 somewhat different from the earlier one just described, 

 although based upon the same lines. Instead of benzoyl- 

 glycollic acid, ethyl benzoate, C0H5COOC2H,,, is em- 

 ployed. This substance is converted readily into benzoyl 

 hydrazine by treatment with hydrazine hydrate : 



Sources of Azoimide and its Derivatives. 



Azoimide and its salts have been obtained from two 

 distinct sources, both organic. One source, the first 

 employed by Prof. Curtius, is benzoyl-glycollic acid, 

 •CgHgCO— O— CH2COOH ; the second is hippuric acid, 

 CfiHsCO— NH— CH.,COOH. During the investigation 

 of the reactions of his previously discovered compound 

 of hydrogen and nitrogen, hydrazine, N0H4, Prof Curtius 

 found that both benzoyl-glycollic and hippuric acids 

 reacted with hydrazine hydrate, forming hydrazine 

 derivatives. 



Benzoyl-glycollic acid reacts with two molecules of 

 hydrazine hydrate, forming benzoyl hydrazine, CgHgCO — 

 NH — NH.,, and the hydrazine derivative of acetic acid, 

 NHo—NH— CH.^COOH, with elimination of water. When 

 benzoyl hydrazine is treated with nitrous acid, it is con- 



.NO 

 verted into a nitroso derivative, CgHsCO — N<^ 



^NHo 

 This nitroso compound is a very unstable substance ; it 

 spontaneously parts with water, and becomes converted 

 irtothe benzoyl derivative of azoimide, benzoyl-azo-imide^ 



C HjCO — N<f . This latter compound forms a direct 



^N 

 starting-point for the preparation of azoimide. Upon 

 boiling with alkalies an alkaline salt of azoimide is 



NO. 1154, VOL. 45] 



CeHsCOOCoH, 



N2H4 . H2O 

 = CcHgCONH— NH., + C2H5OH -I- H^O. 



The benzoyl hydrazine is next treated with sodium 

 nitrite and glacial acetic acid, whereby it is quantitatively 

 transformed into benzoyl azoimide, the benzoyl derivative 

 of the new acid : 



CgHg . CONH— NH., + HNO2 = CgHgCO— N3 + zll^O. 



The benzoyl azoimide thus obtained is finally dissolved 

 in an equal weight of absolute alcohol, and the equivalent 

 of an atom of sodium is also dissolved in a little absolute 

 alcohol, and the two solutions mixed ; the mixture is then 

 digested for several hours upon a water-bath, when the 

 sodium replaces the benzoyl radicle, and ethyl benzoate is 

 regenerated : 



CgHsCO— Ng + C.HsONa = C6H5COOC2H5 + Na— N3. 



Upon cooling, the solution deposits crystals of the 

 sodium salt, and the remainder may be precipitated from 

 the mother-liquor by means of ether. The ethyl benzoate 

 is recovered by distillation with very little loss, and may 

 be employed again for the preparation of a further 

 quantity of the sodium salt of azoimide. 



The sodium salt, NaNj, obtained by this method is 

 substantially pure. It is very soluble in water, but is, 

 strangely enough, not hygroscopic. It is almost insoluble 

 in ether and alcohol. It gives a feebly alkaline reaction, 

 and possesses a briny taste. The crystals do not explode 



