It is a crystalline solid which melts at 56° C. and boils at 204° C. It can only be diazotized in the presence of concentrated sulphuric acid, and even then the free diazonium sulphate is not stable, readily passing in the presence of water to a-oxypyridine.
Hantzsch (Ber., 1901, 34, p. 3337) has shown that in the action of alcohols on diazonium salts an increase in the molecular weight of the alcohol and an accumulation of negative groups in the aromatic nucleus lead to a diminution in the yield of the ether produced and to the production of a secondary reaction, resulting in the formation of a certain amount of an aromatic hydrocarbon.
Nitro compounds have also been prepared by the action of cuprous oxide on diazonium salts (T.
It can be readily diazotized, and the diazonium salt when boiled with alcohol yields aposafranine or benzene induline, C18H12N3.
Kehrmann showed that aposafranine could be diazotized in the presence of cold concentrated sulphuric acid, and the diazonium salt on boiling with alcohol yielded phenylphenazonium salts.
Witt (Ber., 1877, 10, p. 656), is obtained by coupling phenyl diazonium chloride with meta-phenylene diamine.
Alkylated amino-azo-benzenes are also known, and are formed by the coupling of diazonium salts with alkylated amines, provided they contain a free para.
The oxyazo compounds are prepared by adding a solution of a diazonium salt to a cold slightly alkaline solution of a phenol.
Zincke found that the products obtained by coupling a diazonium salt with a-naphthol, and by condensing phenylhydrazine with a-naphthoquinone, were identical; whilst Meldola acetylated the azophenols, and split the acetyl products by reduction in acid solution, but obtained no satisfactory results.
Oeconomides, Ber., 1887, 20, p. 372); and by the action of phenylhydrazine on a diazonium sulphate.
The most easily obtained mixed azo compounds are those formed by the union of a diazonium salt with the potassium or sodium salt of a nitroparaffin (V.
Diazobenzenecyanide, C 6 H 5 N 2 CN, is an unstable oil, formed when potassium cyanide is added to a solution of a diazonium salt.
In order to isolate the anhydrous diazonium salts, the method of E.
In this process the amine salt is dissolved in absolute alcohol and diazotized by the addition of amyl nitrite; a crystalline precipitate of the diazonium salt is formed on standing, or on the addition of a small quantity of ether.
Benzene diazonium nitrate, C 6 H 5 N(NO 3): N, crystallizes in long silky needles.
By the addition of potassium bromide and bromine water to diazonium salts they are converted into a perbromide, e.g.
The diazonium salts are characterized by their great reactivity and consequently are important reagents in synthetical processes, since by their agency the amino group in a primary amine may be exchanged for other elements or radicals.
Replacement of -NH 2 by-OH:-The amine is diazotized and the aqueous solution of the diazonium salt is heated, nitrogen being eliminated and a phenol formed.
Replacement of -NH 2 by halogens and by the - CN and - CNO groups :- The diazonium salt is warmed with an acid solution of the corresponding cuprous salt (T.
In the case of iodine, the substitution is effected by adding a warm solution of potassium iodide to the diazonium solution, no copper or cuprous salt being necessary; whilst for the production of nitriles a solution of potassium cuprous cyanide is used.
Replacement of - NH 2 by - NO 2 :-A well - cooled concentrated solution of potassium mercuric nitrate is added to a cooled solution of benzene diazonium nitrate, when the crystalline salt 2C6H5N2 N03, Hg(N02)2 is precipitated.
Replacement of - NH 2 by hydrogen :-This exchange is brought about, in some cases, by boiling the diazonium salt with alcohol; but I.
Jochem (Ber., 1901, 34, p. 3337), who arrived at the conclusion that the normal decomposition of diazonium salts by alcohols results in the formation of phenolic ethers, but that an increase in the molecular weight of the alcohol, or the accumulation of negative groups in the aromatic nucleus, diminishes the yield of the ether and increases the amount of the hydrocarbon formed.
Hantzsch (Ber., 18 9 6, 2 9, p. 947 1898, 31, p. 1253) has shown that the chlorand bromdiazoniumthiocyanates, when dissolved in alcohol containing a trace of hydrochloric acid, become converted into the isomeric thiocyanbenzene diazonium chlorides and bromides.
Metallic Diazo Derivatives.-Benzene diazonium chloride is decomposed by silver oxide in aqueous solution, with the formation Of benzene diazonium hydroxide, C 6 H 5 N(OH): N.
The free acid is not known; by the addition of the potassium salt to 50% acetic acid at - 20° C., the acid anhydride, benzene diazo oxide, (C6H5N2)20, is obtained as a very unstable, yellow, insoluble compound, exploding spontaneously at o° C. Strong acids convert it into a diazonium salt, and potash converts it into the diazotate.
By the addition of the diazonium salts to a hot concentrated solution of a caustic alkali, C. Schraube and C. Schmidt(Ber., 18 94, 2 7, p. 520)obtained an isomer of potassium benzene diazotate.
These iso-diazotates are formed much more readily when the aromatic nucleus in the diazonium salt contains negative radicals.
Bamberger (Ber., 18 94, 27, p. 9 1 4) obtained the diazoic acids, R NH NO 2, substances which he had previously prepared by similarly oxidizing the diazonium salts, by dehydrating the nitrates of primary amines with acetic anhydride, and by the action of nitric anhydride on the primary amines.
Again, the diazonium chlorides combine with platinic chloride to form difficultly soluble double platinum salts, such as (C 6 H 5 N 2 C1) 2 PtC1 4; similar gold salts, C 6 H,N 2 C1 AuC1 3, are known.
Determinations of the electrical conductivity of the diazonium chloride and nitrate also show that the diazonium radical is strictly comparable with other quaternary ammonium ions.
For these reasons, one must assume the existence of pentavalent nitrogen in the diazonium salts, in order to account for their basic properties.
The isolation of these compounds is a powerful argument in favour of the Hantzsch hypothesis which requires the existence of these three different types, whilst the Bamberger-Blomstrand view only accounts for the forma tion of two isomeric cyanides, namely, one of the normal diazonium type and one of the iso-diazocyanide type.
Benzene diazonium hydroxide, although a strong base, reacts with the alkaline hydroxides to form salts with the evolution of heat, and generally behaves as a weak acid.
On mixing dilute solutions of the diazonium hydroxide and the alkali together, it is found that the molecular conductivity of the mixture is much less than the sum of the two electrical conductivities of the solutions separately, from which it follows that a portion of the ions present have changed to the non-ionized condition.
This behaviour is explained by considering the non-ionized part of the diazonium hydroxide to exist in solution in a hydrated form, the equation of equilibrium being: C6H6.N.
Hantzsch, Ber., This assumption also shows the relationship of the diazonium hydroxides to other quaternary ammonium compounds, for most of the quaternary ammonium hydroxides (except such as have the nitrogen atom attached to four saturated hydrocarbon radicals) are unstable, and readily pass over into compounds in which the hydroxyl group is no longer attached to the amine nitrogen; thus the syn-diazo hydroxides are to be regarded as pseudo-diazonium derivatives.
Hantzsch explains the characteristic reactions of the diazonium compounds ky the assumption that an addition compound is first formed, which breaks down with the elimination of the hydride of the acid radical, and the formation of an unstable syn-diazo compound, which, in its turn, decomposes with evolution of nitrogen (Ber., 18 97, 30, p. 2 54 8; 1898, 31, p. 2053).
Soc., 1907, 91, p. 1049) suggested a quinonoid formula for diazonium salts, which has been combated by Hantzsch (Ber., 1908, 41, pp. 353 2 et seq.).
NHR, may be prepared by the action of the primary and secondary amines on the diazonium salts, or by the action of nitrous acid on the free primary amine.
Nitrous acid converts them, in acid solution, into diazonium salts.
Diazoimino compounds, R N3, may be regarded as derivatives of azoimide; they are formed by the action of ammonia on the diazoperbromides,or by the action of hydroxylamine on the diazonium sulphates (J.
It exists in two crystalline forms. Nitric acid passed into its chloroform solution gives phenyl diazonium nitrate.
Diazo-Amines.-The diazo-amines, R N: N NHR I, are obtained by the action of primary amines on diazonium salts; by the action of nitrous acid on a free primary amine, an isodiazohydroxide being formed as an intermediate product which then condenses with the amine; and by the action of nitrosamines on primary amines.
The diazonium salts are also formed by the action of zinc-dust and acids on the nitrates of primary amines (R.