A CLASSIFICATION OF COMPOUNDS OF HYDROGEN AND NITROGEN* L. F. AUDRIETH, UNIVERSITYOP ILLINOIS, URBANA, ILLINOIS Most elements form hydrogen compounds, but in only a few instances is the capability of forming more than one hydride definitely expressed. The existence of a series of hydrides of one and the same element has been ascribed to the power of self-linkage which these possess. This property is most highly accentuated in the case of carbon and accounts for the multiplicity of carbon compounds and the extensiveness of organic chemistry. As might be expected, this characteristic is also expressed by several of the other elements of the fourth group-however, to a diminishing degree as the atomic weights of the elements increase. The silanes, germanes, and stannaues give evidence of this fact. Elements in the neighboring groups likewise exhibit self-linkage and attention is called to the large number of boranes which have been prepared. To the right of carbon we find that phosphorus and nitrogen, and to a lesser extent sulfur and oxygen, manifest self-linkage and form series of hydrides, or compounds which are derivatives of such hydrides. Among the latter may be mentioned the alkyl and aryl substitution products which are considerably more stable than the parent substances. In many cases the hydrogen compounds are unknown, but their substitution products are well defmed and characterized. In the number and variety of such derivatwes the element nitrogen ranks next to carbon. Since many of the nitrogen compounds are ones in which substitution of alkyl and aryl groups for the hydrogen atoms has taken place, they have been and still are considered as organic compounds. Yet, when considered from the point of view of the parent substances, the hydronitrogens, a classification is possible which the chemistry of organic nitrogen compounds has heretofore lacked. Furthermore, it becomes possible to simplify the chemistry of these substances by a consideration of type reactionsthese having been obscured largely because the attached carbon radicals have been regarded as of paramount importance. The hydronitrogens are those compounds known either in the free state or in the form of their derivatives, which are related to nitrogen chemistry as the hydrocarbons are to organic chemistry. As in the case of the hydrocarbons, various groups or homologous series of hydronitrogens may be construed possessing given type formulas, which depend upon the degree of saturation or the presence of double and triple bonds. The simplest of all nitrogen hydrides, the methane analog of nitrogen, is ammonia. I t forms the first member of the saturated series of hydroThe two lower members of nitrogens whose type formula is N,H,+,. * Presented before the Illinois Academy of Sciences in April, 1930. 2055
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this series are known in the free state, the others only in the form of their organic derivatives. The saturated series is given in Table I. TABLE I
Saturated Hydmnitrogens NHa NSHI NaHr NIH~
Type formula N.H,+* Ammonia Hydrazine (diamide) Triazane (prozane) Tetrazane (buzane, hydratetrazone)
HrN HDNH* HnN,NH.NH2 HnN.NH.NH.NH2
Unlike the methane series the individual members of the saturated series of hydronitrogens differ very decidedly from one another. Liquid ammonia as a parent solvent has been investigated quite thoroughly by many workers, in particular by Kraus, Franklin, and Cady.* I t has been shown to be an excellent ionizing solvent and reactions have been found to take place in it with a facility which is surprising. Indeed, the study of nitrogen compounds, particularly the hydronitrogens and their derivatives, should be carried out in this solvent in preference to all others. Its character as a basic solvent by virtue of its affinity for the proton has permitted the investigation and characterization of many substances as acids which do not behave as such in more acidic solvents. Its affinity, not only for the proton but also for metallic ions, has given rise to the formation of many association compounds, chief among which are the ammonium salts and metal ammines. Hydrazine, first prepared in the anhydrous state by Lobry de Bruyn ( I ) , resembles ammonia in that it also acts as a parent solvent (2) in the anhydrous state. Like ammonia it forms solvates and association compounds. I t is less basic in nature than ammonia. Its character as a reducing agent is accentuated to a marked degree over ammonia. The oxidation of hydrazine under certain conditions leads to a variety of products among which hydrazoic acid, nitrogen, and ammonia, have been identified. The mechanism of this reaction has been the subject of considerable investigation by Browne (3) and his co-workers and has lately led to a classification of oxidizing agents based upon the character of the products obtained. Oxidation of various organic hydrazines gives rise to derivatives of the higher hydronitrogens which will be discussed subsequently (4). The triazanes (5) are a group of compounds, few in number, ill-defined, and in need of further study. They may be prepared by the reduction of triazenes. They are very unstable and undergo rapid decomposition.
* For a summary of reactions in liquid ammonia,the reader is advised to consult the excellent series of articles by Fernelius and Johnson which have been published in the J. CWM.Eouc. See p. 1850 of August. 1930, issue for complete references.
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CLASSIFICATION OF COMPOUNDS
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The tetrazanes form a larger and more interesting group. They are readily obtainable by the oxidation of tri-substituted hydrazines (1) 2RsN.NHR
+ 0 = RnN.NR,NR.NRz+ H20
(1)
Certain of the tetrazanes, such as hexaphenyltetrazane ( 6 ) , exhibit thc phenomenon of dissociation to form free nitrogen radicals, such as triphenylhydrazyl (2). [(GHr),N.NCsHsIr = 2(C6H~)nN.N-CsHa i
(2)
This behavior is simply an expression of the reluctance of nitrogen to form long chains. Thus, there is exhibited by many of the tetrazanes a tendency toward stabilization by dissociation. Hydroxylation of the lower members of the saturated series leads to a number of rather interesting derivatives. Thus, successive hydroxylation of ammonia gives hydroxylamine, dihydroxylamine, and nitrous acid.
+
NH84 NH(OH), 4 N(OH),
1 1
NOH
HNOI
HsN20s
Hydroxylamine resembles both ammonia and hydrazine in its reactions and properties. I t also constitutes the parent substance of a solvent system and, because of its pronounced &nity for the proton, may be classed as a basic solvent (7). Dihydroxylamine is a hypothetical intermediate reduction product of nitric acid, which is so unstable that it has never been isolated. Its dehydration product, nitroxyl (S), polymerizes rapidly to f o m hyponitrous acid. That it does exist for a very short time is indicated by the fact that it combines, a t the moment of formation, with aldehydes to form hydroxamic acids and with nitroso compounds to give nitrosohydroxylamines (3). Its formation in the oxidation of hyNOH NOH
+ RCHO = RC(0H)NOH + CaHsNO = CaHdrl(N0)OH
(3)
droxylamine (9) has been postulated to account for the variegated character of the reaction products (4). NHpOH
+ 0 = NOH + HsO TABLE II
Unsaturated Hydronitrogens N& N8Hs NIHl
NrHr
(a) T y p Forrnuh N.& HN:NH Diiide Triazene (diazoamine) HN:N,NHz H2N.N:N.NH1 Tetrazene (tetrazone) Isotetrazene (diazohydrazine,buzylene) HN:N.NH.NH* maa Ammonium azide Hydrazine azide NzHdrla
(4)
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NsH
(b) Type Formula N,H.-* N Hydrogen azide, hydrazoic acid, azoimide, hydronitric acid, triazoic acid H N : N ~ N O ~ H N N< I ~
N,Hs ? NrHa N& ?
Diiminohydrazine Bisdiazoamine Bisdiazohydrazine
NsH4
Octazotriene (octazone)
(6)
HN:N.N:NH HN:N.NH.N:NH HN:N.NH.NH.N:NH Type Formula N,H,-&
HN:N.NH.N:N.NH.N:NH
The N,H. Series The members of the N,H, series are all characterized by the presence of a double bond. The simplest member of this series is diimide, the parent substance of the large group of azo compounds. Many attempts have been made to prepare the ethylene analog of the hydronitrogens, but those reactions which were expected to lead to its isolation invariably gave equimolecular mixtures of hydrogen and nitrogen. Hydroxydiimide, HON :NH, a hypothetical intermediate in the decomposition of ammonium nitrite (lo),may be regarded as the parent substance of the diazo compounds. Where the formation of alkyl derivatives of hydroxydiimide is involved stabilization is effected by the splitting off of water to give such compounds as diazomethane, which may possess either the cyclic or the chain structure (5).
It is interesting to note in this connection that the formation of aryl diazo compounds by the action of an amine upon nitrous acid is equivalent to an ammonolysis, more strictly an "aminolysis" of nitrous acid (6).
Triazene, the parent substance of the diazoamino compounds, has been obtained in aqueous solution by the reduction of ammonium azide (11) at low temperatures using a zinc-copper couple and ammonium chloride. I t may be regarded as a deammonation product of ortho-ammono-nitrous acid (theoretically an isomer of tetrazene). Actually, the diazoamino compounds are obtained by the action of aryl amines in excess upon nitrous acid or diazo compounds. These reactions are therefore solvolytic in nature and involve the complete replacement in nitrous acid of the last vestiges of the water system (7).
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The monosubstituted triazenes (12), which are considerably less stable, have thus far been prepared only by the reduction of the correspondimg azides (8). RNa
+ 2H = R N : N . NHz
(8)
Hydroxytriazenes are obtainable by the action of hydroxylamine upon diazo compounds (9).
+
= RN:N.N R N : N,$OH -~-- - -- -HcNOH -,
I
(9)
H
Three compounds may be formulated which possess the empirical composition N4H4. One of these, ammonium azide, is a white crystalline solid, very explosive, which is interesting in view of the fact that on thermal decomposition it yields the largest volume of gas per unit weight of any known substance. The other two substances, tetrazene and isotetrazene, are known only in the form of their organic substitution products. The tetrazenes (13) are obtainable by the oxidation of asymmetrical disubstituted hydrazines (10). They undergo pyrolysis in various organic 2 R z N . N H a + 2 0 = R2N.N:N.NR1
(10)
solvents with the evolution of nitrogen and the formation of tetrasubstituted hydrazines (11). R,N . N : N .NR9
+ heat = R2N.NR. + NI
(11)
The isotetrazenes result from the interaction of diazo compounds with mono- and disubstituted hydrazines. Unlike the tetrazenes, they decompose upon heating to yield the corresponding amines and azides (12).
.
.
R'N :N NH NHR"
+ heat = R'Ns + R"NH2
The N,H,-,
(12)
Series
The simplest member of this series, hydrazoic acid, HNs, was first isolated by Curtius (14) and has been the subject of considerable investigation since its discovery. The free acid is extremely explosive and very toxic. Its salts, in particular the heavy metal compounds, are very explosive and have found some application as detonators in priming caps. The alkali and alkaline earth azides (15) decompose upon heating to give the free metals and nitrogen. This reaction has been employed in the preparation of metallic radium. The N3- radical has been termed a "halogenoid (16) group, since it exhibits halogen-like properties in the formation of such compounds as chlorazide, CINs, bromazide, BrNs, etc. The alkali and alkaline earth azides condense with carbon disulfide to give azidodithiocarbonates (17) salts of azidodithiocarbonic acid, HSCSNa (13). These salts simulate the azides in their explosive properties. OxiMNI
+ CSp = MSCSNs
(13)
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dation of azidodithiocarbonates results in the formation of an extremely unstable disulfide, azidocarbondisulfide, (SCSNs)r (18) which is likewise halogenoid in its properties and closely related to the thiuram-disulfides
Most methods for preparing hydrazoic acid or its substitution products involve the action of nitrous acid or one of its derivatives upon hydrazine or substituted hydrazines. These facts have caused Browne (19) to look upon hydrazoic acid as a hydrazo-nitrous acid, obtainable by the solvolytic action of hydrazine upon nitrous acid (15). Franklin (ZO), however, has pointed out that hydrazoic acid is a strong delectronator
and may be regarded as a deammonation product of ortho-ammono-nitric acid (16). That such a postulation is in accord with the facts is evidenced N(NH& = HNI
+ 3NHa
(16)
by the solubility of the noble metals in a mixture of hydrochloric and hydrazoic acids and by the nitridizing action of potassium azide in the conversion of potassium cyanide, an ammono-carbonite, to potassium cyanamide, an ammono-carbonate (17). Its preparation by the action KNs
+ KNC = KnNCN + NI
(17)
of fused potassium amide upon potassium nitrate is further support in favor of this postulation. The reduction of hydrazoic acid and its derivatives leads to a variety of products depending upon the character of the reducing agent and the nature of the substituent groups. From a consideration of hydrazoic acid as an ammono-nitric acid this mechanism becomes clear by analogy with the Bancroftian theory for the reduction of aquo-nitric acid. HNOI --t HNOI + (HO)rNH + HINOH -+ NH, HN. + HaN8 --t (HaN)~NH + HzN.NH2 + NHs Triazene Triazane Hydrazine Ammonia Hydrazoic acid 4 -NHa Diimide Tetrazane 0 + NaH, N4H4/\NIL, Tetrazene Isotetrazene
The nitridation of hydrazine to give hydrazoic acid is quite analogous to the complete oxidation of hydroxylamine to nitric acid. This mechanism is, furthermore, interesting as it brings together the inter-relationship of the whole group of hydronitrogens and their consideration as ammono compounds from the Franklin point of view.
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The multiplicity of the reactions of organic azides makes their study an extremely interesting one. Condensation with hydrogen cyanide, nitriles and cyanogen halides leads to the formation of tetrazole derivatives (18).
Reduction offers the only known method for preparing mono-substituted triazenes. No derivatives of diiminohydrazine or of bisdiazohydrazine have as yet been prepared. The bisdiazoamino compounds are well known and easily obtainable by the interaction of diazo compounds in excess with ammonia and amines. The octazotrienes (21) may be obtained by the gentle oxidation of 1,2-disubstituted isotetrazeues (19). The resulting compounds form the
longest nitrogen chains. They are very unstable and decompose readily to give triazenes and nitrogen. Summary 1. Homologous series of hydronitrogens exist. A consideration of organic nitrogen compounds as derivatives of these would do much to clarify our knowledge concerning them. 2. Nitrogen exhibits self-linkage to a remarkable degree, but not to the extent of carbon. The hydrocarbons are stable, whereas most of the hydronitrogens are so unstable that they cannot be obtained in the free state. Even their organic substitution products undergo ready decomposition. Experimental evidence thus far accumulated indicates that chains of more than eight nitrogen atoms are probably non-existent. 3. Individual members of the homologous series of hydronitrogens show no great similarity, but rather a deaded diversity in properties. Here again do they differ from homologous series of hydrocarbons. They are, however, very much more reactive and undergo oxidation, reduction, and chemical change very readily. 4. It is suggested that the hydronitrogens be studied with particular reference to liquid ammonia as the parent solvent.
Literature Cited (1) DE BRUYN,Rec. Bav. chim., 14, 82 (1895). J. Am. Chem. Soc., 37, 816, 825 (1915). (2) WELSHand BRODERSON, (3) IQnn and BROWNE, Ibid., 50, 337 (1928). (4) WIVI&LAND, "Die Hydrazine," Stuttgart, 1913.
JOURNAL OF CHEMICAL EDUCATION (5)
(6) (7) (8) (9) (10) (11) (12) (13) (14)
(15) (16) (17) (18) (19)
(20) (21)
1930 SB~XBER ,
THIELEand O s n o m , Ann., 305, 80 (1899); DXELSand AUEART, Ibid.,.UP, 28 (1922). Go~~scmnuT, Ber., 53B, 44 (1920); 55B, 616 (1922). A ~ R I E T HProc. , Ill. Acud. Sciences,'22, 385 (1929). ANGELI,Gazz. chin. ital., 30 (I), 593 (1900); Ber., 37, 2390 (1904). KURTENAC~ER and NSU~SSR, Z. anorg. Chem.. 131, 27 (1923). A ~ R I E T HJ., Phys. Chem., 34, 538 (1930). D~ROTH and PPISTER, Ber., 43, 2757 (1910). DIMROTH, Ibid., 40, 2376 (1907); 43, 2757 (1910). E. FISCHER,Ann., 190, 67 (1878). CURTIUS,3. firakt. Chem., 43, 207 (1891). SUHRMANN and CLUSIUS, 2. anorg. Chem.. 152, 52 (1926). WALDSNand A U D R I E ~Chem. . Rm.. 5, 339 (1928). and AuBROWNE and HOEL,J. Am. Chem. Soc., 44, 2315 (1922); BROWNS DRIETH. Ibid., 49, 917 (1927). BROWNS,HOEL,Smm. and SWEZEY,Ibid., 45, 2541 (1923). BROWNSand WII.COXON, Ibid., 48, 682 (1926). FRANKLIN. Ibid., 46, 2137 (1924). WOHLand ScnmP, Ber., 33, 2741 (1900).
