270 CHATTAWAY: THE OXIDATION OF AROMATIC HYDRAZINES

XXV.-The Oxidation of Aromatic Hydyaziizes by Metallic Oxides, Permangalzates, and Chromates.

By FREDERICK DANIEL CHATTAWAY.

THE extraordinary ease with which aromatic hydrazines are destroyed by oxidising agents has been referred to by most chemists who have worked on them,* and diazonium salts have been universally regarded as the primary products of their oxidation.

The behaviour of these substances when oxidised by free oxygen in alkaline solution (Chattaway, Trans., 1907, 91, 1323) having made this generally accepted view seem improbable, a number of experi- ments have been carried out on their oxidation in presence of alkalis by various metallic oxides and highly oxygenated salts. The results may be stated in general terms as follows.

Primary aromatic hydrazines are readily attacked by most sub- stances capable of giving up oxygen a t all easily, the products being in the main the same as when free oxygen is used.

Theaction which takes place to a predominating extent causes the liberation of nitrogen and the replacement of the hydrazino-group by hydrogen. This main action is generally accompanied by secondary ones, which take place to a comparatively very small, but varying, extent ; hydrocarbons of the diphenyl group containing t w o of the aromatic residues linked together are produced, a little tarry matter is frequently formed, and sometimes, i n still smaller quantity, simple azo-derivatives, as, for example, azobenzene. Phenols may be formed in small quantity, but only when the oxidising agent employed acts very energetically. Diazo-compounds are never produced when the oxida- tion is carried out in alkaline solution, but only in presence of a

++ Compare Fischer, Annulen, 1878, 190, 67, and 1879, 199, 281 ; Fischer and Ehrhard, Annalen, 1879, 199, 333; Haller, Bet-., 1885, 18, 90; Zincke, Ber., 1885, 18, 786; Btrache, Monutsh., 1891, 12, 623, and 1893, 13, 316; Wurster, Ber., 1887, 20, 2633.

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BY METALLIC OXIDES, PERMANGANATES, AND CHROMATES. 271

considerable excess of some strong acid. Azoimides are formed when alkalis are absent and the hydrazines are present in excess.

The nature of the oxidising agents and the conditions of the experi- ments naturally affect the rate of action. All oxides act more vigorously when hydrated and when finely divided, and action becomes much more rapid as the temperature is raised.

If the basic oxide of the metal is easily reduced, the metal itself is liberated, as with the oxides of mercury, copper, and silver; in other cases, the peroxides only act, and the basic oxide is formed, as with the peroxides of lead and manganese.

Alkaline permanganates act very energetically at the ordinary temperature, whilst with chromates the temperature has to be raised considerably before any appreciable evolution of nitrogen occurs.

Potassium chromate oxidises all primary aromatic hydrazines very easily, giving a practically theoretical yield of nitrogen and hydrocarbon, and being itself reduced to potassium and chromium hydroxides. This reaction affords the most convenient method yet described for replacing a hydrazino- or amino-group by hydrogen, the latter being first converted into the former through a diazonium salt.

If the reduction of copper oxide by pheuylhydrazine is carried out under suitable conditions, the metal set free can be deposited on glass in the form of a coherent metallic film, equalling in brilliancy a similarly deposited film of silver, and showing the splendid red colour of polished copper.

The view of the course of the reaction recently put forward to explain the oxidation of hydrazines by free oxygen (Chattaway, Trans., 1907, 91, 1323) affords, with a suitable extension, a simple explana- tion of all the facts observed.

When either oxygen or an oxidising agent acts on a primary aromatic hydrazine, one of the hydrogen atoms of the hydrazino- group is first attacked, and a hydroxphydrazine is produced,* thus :

R*NH*NH, + 0 = R*NH*NH*OH. This substance, however, not being stable in presence of alkalis,

undergoes disruption during some phase of its motion, thus :

R*N*H R N H H&-OH * H N OH

I 3- 111 + I

the splitting off of hydrocarbon and water occurring either in one or two stages.

If, however, a very energetic oxidising agent is used, a certain number of molecules may, before breaking down, undergo a further

* Probably t h e action which first takes place is the addition of two hydroxyl groups to t h e nitrogen which thus develops its quinquevalency.

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272 CHATTAWBY : THE OXIDATION OF AROMATlC HYDRAZINES

oxidation, a second hydrogen atom being thus replaced by another hydroxyl group. The similar breaking down of this molecule under the influence of the alkali results in the formation.of a phenol :

R*N*H. R N H -+ 3. # + (IH * H O ~ ~ O H

I n the absence of an alkali which acts as catalytic agent and much accelerates the decomposition of these hydroxyhydrazines, the intro- duction of the second hydroxyl group takes place to a much greater extent, and in the presence of a sCvrong acid at a low temperature a diazonium salt may be formed, thus :

R*N*H R*N*C1 + HCl = + 2H,O. HO&OH N

The subsidiary reactions, for example, the production of hydrocarbons of the diphenyl series and of azo-derivatives in presence of alkalis or of azoimides in absence both of alkalis and of acids, can be simply explained by the interaction of two molecules of the hydroxyhydrazines primarily formed. Among the products of the oxidation of primary aromatic hydrazines in presence of alkalis, even when carried out at a low temperature, no diazo-compounds can be detected. This makes i t highly improbable that they are ever formed, the breaking down of the oxidised molecule taking place at a stage in the oxidation before the one at which they could be produced. The production of phenols in small quantity when energetic oxidising agents are used shows that, even if this second stage is reached and two hydroxyl groups are introduced into the molecule, it does not split off water in presence of alkalis, but undergoes the same type of decomposition as when only one such group is present.

This is in agreement with the well-known behaviour of diazonium compounds, these only undergoing the characteristic diazo-decomposi- tions in presence of agents able to form additive compounds with them ; for example, water, alcohol, or cuprous chloride, thus giving to the molecule a structure analogous to that of the hydroxy-compounds figured above.

It is unnecesary to assume as Hantzsch does (Be?*., 1900, 33, 2517) that this addition is followed immediately by a partial decomposition resulting in the formation of an unstable syn-diazo-compound which then breaks down. A much more probable explanation is that diazo- compounds as such do not break down with elimination of nitrogen, this only taking place in a molecule where each nitrogen atom carries at least two suitably related groups attached to it, the single linking of the nitrogen atoms now giving the mobility necessary for re-arrange- ment of the molecule before its disruption. Thus taking three

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BY METALLIC OXIDES, YERMANGANATES, AND CHROMATES. 273

examples, we should represent the introduction of a hydroxyl group, an ethoxyl group, or a hydrogen atom and a chlorine atom thus :

R*N*SO,H R*N*SO,H R N H O ~ T - H HO N -+ I + I I I + H2S04. I l l +H,O -+

N

R*N*Cl R N C1 -+ 1 + l l I + l 71 HAO~C,H, H N O.CH,*CH, ++

R*N*C1 8 +C,H,*OH / R N

I + I I I +HCl. \ R*N*Cl

C,H~*O&H -+ c,H,- o N

R*N*Cl R N C1 Cl*N*Cu c1 N c u

I - + I + I l r + r '

The views here advanced afford an insight into what occurs in a number of reactions which have hitherto received no satisfactory explanation, to give an instance, the behaviour of diazonium salts on reduction. As is well known when diazonium salts are reduced by stannous

chloride in presence of a large excess of hydrochloric acid, they are converted practically quantitatively into hydrazines, this being a common method of preparing the latter compounds (Meyer and Lecco, Ber., 1883, 16, 2976). When, however, an excess of acid is not used, reduction by stannous chloride gives rise to a number of quite different products, in which the aryl group present in the diazonium salt is united with hydrogen, chlorine, hydroxyl, amidogen, or the azoimide complex (Culmann and Gasiorowski, J. p. Chem., 1889, [ii], 40, 97 ; Effront, Ber., 1884, 17, 2329); to take the simplest case, whilst benzenediazonium chloride yields chiefly benzene, considerable quantities of chlorobenzene, phenol, aniline, and phenylazoimide are also produced.

Again, when a diazonium salt is treated with an excess of caustic alkali and then reduced by a strongly alkaline solution of stannous oxide, nitrogen is vigorously evolved and the diazonium group is replaced by hydrogen, whilst an azo-derivative is formed in small quantity (Friedlander, Ber., 1889, 22, 587) ; for example, benzene- diazonium chloride thus reduced yields benzene mixed with about one- tenth of its weight of azobenzene (Koenigs and Carl, Ber., 1890, 23, 2672). Complete conversion of a diazonium salt into a hydrazine by reduction, or of a hydrazine into a diazonium salt by oxidation, is only

* The aldehyde and hydrogen chloride liberated are, without any doubt, formed by the breaking down of ethyl hypochlorite, C 'H, 'CH,*OC14 HC1+ CH;CHO. This change can be followed when a nitrogeu chloride is decomposed by alcohol.

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274 CHATTAWAY : THE OXIDATION OF AROMATIC HYDRAZINES

possible in presence of excess of acid, whilst complete elimination of tbe nitrogen and replacement of the hydrazine or diazonium group by hydrogen through the agency of oxidising or reducing agents respectively is only possible in presence of excess of alkali.

When neither acid nor alkali is present in excess, the compounds produced in the oxidation of hydrazines are exactly those obtained in the reduction of diazonium salts.

These actions can all be satisfactorily explained by the assumption of the formation in each of them of the same type of intermediate com- pound, a hydroxyhydrazine which i.9 relatively stable in presence of stroDg acids, but which immediately undergoes the typical diazo-decomposition in presence of alkalis. The actions by which azoimides and anilines and azo-derivatives are formed, although more complex, because requiring the interaction of two molecules of the hy droxyhydrazine, only involve intramolecular rearrangements of exactly the same type.

Oxidation of Pl~enyl-, 0-Tolyl-, p-Tolyl-, pBromopAeny1-, a- Naphth& and /3-Niphthyl-hydlmxine by Metallic Oxide8.

As phenylhydrazine is much more readily attacked than the others, and as the actions which take place are typical, the beliaviour of the various oxides with it alone are described.

To ascertain the act,ion of anhydrous oxides, the finely-divided solid was suspended in about twenty times its weight of water and the calculated amount of phenylhydrazine added, the liquids being shaken for a few moments to mix them thoroughly. The hydroxides were prepared immediately before adding the phenylhydrazine by de- composing a salt of the metal dissolved in about twenty times its weight of water with the calculated quantity of potassium hydroxide.

The action of dry precipitated mercuric or mercurous oxide or the corresponding hydroxides on phenylhydrazine is very vigorous ; much heat is developed, benzene is formed, and nitrogen liberated so rapidly that the liquid froths violently. The action of crystalline mercuric oxide, although vigorous, is not so violent.

Both dry and freshly precipitated silver oxide act less energetically on phenylhydrazine than the corresponding mercury compounds, the same prodxcts resulting.

Freshly-precipitated cupric hydroxide decomposes phenylhydrazine similarly, the liquid becomes warm, benzene is formed, and nitrogen is given off rapidly. Dry cupric or cuprous oxide acts much more slowly, and even on boiling the liquid very little evolution of of nitrogen is noticed.

In all these cases, the oxide is completely reduced and the metal is set free.

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BY METALLIC OXIDES, PERMANGANATES, AND CHROMATES. 275

Lead peroxide acts immediately on phenylhydrazine, the liquid becomes warm, nitrogen is evolved with effervescence, and the peroxide is reduced to the basic oxide, whilst benzene together with a little azobenzene and diphenyl are produced. Red lead, however, has very slight action on phenylhydrazine. Manganese dioxide acts somewhat less readily than lead dioxide ; the products of the oxidation, however, are the same, and the dioxide is similarly reduced to the basic oxide.

Phenylhydrazine is also oxidised by ferric hydroxide, but the action is very slow.

When copper oxide is thus reduced by phenylhydrazine, the metal, under suitable conditions, can be deposited on the glass in the form of a fine mirror. If small fragments of oxidised copper wire are heated on a water-bath for some considerable time in a saturated aqueous solution of phenylhydrazine, although the evolution of nitrogen is so slow that it can scarcely be noticed, copper is deposited on the glass immediately underneath the fragment in small, brilliant patches. By moving the pieces of oxide about, a copper mirror can be obtained of considerable size, but not of uniform brightness. If to an aqueous solution of phenylhydrazine saturated at ZOOo and gently boiling in a clean, new flask there is added a little potassium hydroxide and then, in very small quantities, finely-divided black copper oxide, obtained by heating the nitrate, it rapid evolution of nitrogen takes place and a small quantity of the oxide passes into solution. I n this solution, the metal exists in the cuprous state dissolved in the phenylhydrazine, and can be precipitated as cuprous hydroxide by the addition of excess of potassium hydroxide. If such a solution is gently boiled and more solid oxide added from time to time as i t dissolves, a very fine copper mirror can be obtained, the whole interior of the flask becoming slowly coated with a firm coherent film of the metal similar to the film of silver obtained when silver oxide is reduced by aldehydes or tartrates. It is, however, somewhat difficult to obtain a good deposit by this method, and it is easier to employ a solution of cupric hydroxide in ammonia.

The following procedure, which resembles that employed in silvering glass, gives a uniformly excellent result. Heat a mixture of one part of freshly distilled phenylhydrazine and two parts of water until a clear solution is obtained, and to t h i s add about half its bulk of a warm saturated solution of cupric hydroxide in strong ammonia. Nitzogen is freely evolved during the addition, and the cupric is reduced to cuprous hydroxide, which remains dissolved in the ammoniitoal liquid and does not undergo any immrdiate fulther. reduction. Atld oext a hot 10 per cent. solution of potassium hydruxicir uutil a slight permanent precipitate of cuprous hydroxide is produced. If this

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2'76 CHATTAWAY: THE OXIDATION OF AROMATIC HYDRAZINES

colourless or pale yellow liquid be now cautiously heated in contact with a perfectly clean glass surface, metallic copper is deposited on it in the form of a thin, coherent, perfectly reflecting lamina. To obtain a film of suficient thickness, it is best not to pour off tbe warm reducing fluid, but to allow it to remain in the flask until quite cold. When th'e liquid is poured off, the film of copper should be well washed first with water, and afterwards with alcohol and ether. It should then be protected from the slow oxidising action of the air by one or two coats of some quickly drying varnish.

Oxidation of Hydraxines by Potassium Pmanganate.

Aromatic hydrazines are very readily oxidised by potassium permanganate either in the presence of acids or alkalis. In presence of a small quantity of sulphuric acid, a complicated series of actions occurs. Although simple hydrocarbons and nitrogen are the main products, hydrocarbons analogous to diphenyl and azo-derivatives are formed in small quantity, whilst a considerable amount of t a r is produced. Some chloro-subst ituted hydrocarbon may be formed if hydrochloric instead of sulphuric acid is present.

It is possible that diazonium compounds are formed in these reactions, but, if so, they must be produced in very small amount, as in spite of careful search they could not be recognised with certainty.

To give the details of one experiment, 2.7 grams of phenylhydrazine were dissolved in 30 grams of sulphuric acid diluted with 200 C.C. of water, This solution, cooled to Oo, was poured over 500 grams of crushed ice, and to it was added a similarly cooled solution of 3-2 grams of potassium permanganate in 500 C.C. of water. Considerable efferves- cence occurred, and benzene could be recognised by its odour ; the red colour of the permanganate completely disappeared, and a small quantity of a brown solid, probably manganese dioxide, separated. A cold saturated solution of potassium hydroxide was next added until the liquid showed a strongly alkaline reaction. It was then filtered, the temperature of the liquid near being allowed to rise above Oo. To the clear, cold alkaline liquid a solution of 4 grams :of /3-naphthol in a slight excess of dilute potash was added. No red colour was produced, nor did any develop on allowing the liquid to stand for twenty-four hours.

The oxidation of hydrazines by permanganate in presence of alkalis, on the other hand, follows a simple course.

All primary aromatic hydrazines are readily oxidised at the ordinary temperature by an aqueous solution of potassium permanganate made alkaline with potassium hydroxide. As when other oxidising agents are used considerable rise of temperature takes place, the

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BY METALLIC OXIDES, PERMANGANATES, AND CHROMATES. 277

hydrazino-group is replaced by hydrogen, and nitrogen is rapidly evolved. A little of some hydrocarbon of the diphenyl group is produced, and some azo.derivative is formed together with a varying quantity of tarry matter. The permanganate, if in excess, is reduced to manganese dioxide, whilst the latter is further reduced to manganous oxide by excess of the hydrazine.

The amount of each of these products formed mas determined in a number of cases, but the quantitative results obtained are of little impor tance.

The action of alkaline permanganate on phenylhydrazine, p-bromo- phenylhydrazine, and 0- and p-tolylhydrazine has been studied.

On adding phenylhydrazine to an excess of a saturated solution of potassium permanganate, made strongly alkaline with potassium bydroxide, until the red colour of the permanganate disappeared, a violent evolution of nitrogen took place, and the temperature of the liquid rose considerably. All the benzene formed could not be collected, since much was carried away in the form of vapour by the rapidly escaping nitrogen. When violent action was over, the remainder of the benzene was driven off in a current of steam; on continuing the passage of steam for some time, a small quantity of diphenyl and a considerable amount of azobenzene slowly distilled over. On separating the mangarese dioxide, acidifying the strongly alkaline filtrate with sulphuric acid, and extracting with ether, a very small quantity of an oily, strongly smelling substance, apparently phenol, mas obtained ; the amount, however, was so small that it could not be identified with certainty.

Similar experiments, using an excess of phenylhydrazine and a known quantity of permanganate, did not yield constant quantitative results.

Several attempts were made to discover if a diazo-compound is produced in the action, but without result, the amount of such compound if it is produced a t all must therefore be very small.

To give the details of one experiment, 4.2 grams of potassium permanganate and 10 grams of potassium hydroxide were dissolved in 400 C.C. of water, the solution was cooled to Oo, and poured over 200 grams of crushed ice. To this was added a similarly cooled solution of 5 grams of phenylhydrazine and 10 grams of potassium hydroxide i n 400 C.C. of water. As the hydrazine solution was added, nitrogen was rapidly given off, the odour of benzene became evident, and the red permanganate solution became first green from the production of manganate and finally brownish-black from the deposition of hydrated manganese dioxide. The addition of the phenylhydrazine solution was hontinued until the green colour just disappeared. The manganese dioxide mas then filtered off, and the clear, cold alkaline liquid mixed

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278 CHATTAWAY : THE OXIDATION OF ABOMATlC HYDRAZINES

with a solution of 4 grams of @-naphthol in a slight excess of aqueous potassium hydroxide. Not the slightest red colour was produced, nor did any develop on allowing the liquid to stand for twenty-four hours.

The amounts of diphenyl and akobenzene formed were ascertained by reducing a known weight of the mixture and determining the amount of diphenyl remaining.

The other hydrazines mentioned behave with potassium perman- ganate similarly to phenylhydrazine.

Oxidation of Hydvazines by AZkaZine Dichromates and Chromates.

Hydrazines are readily oxidised by dichromates at the ordinary temperature, and by chromates i f the temperature is somewhat raised. I n each case, the action is a simple one, the dichromnte and chromate alike being converted into a1 kaline hydroxide and hydrated chromium sesquioxide, whilst the hydrazine yields the hydrocarbon or substituted hydrocarbon and nitrogen. A very little diphenyl or other hydro- carbon of this group is produced, and only when dichromates are used is any appreciable amount of azo-derivative obtained. Only a t first is there any difference in the behaviour of dichromates and chromates, as the former are soon converted into the latter by the alkaline hydroxide liberated. The actions are represented by the following equations :

K2Cr207 + 3R*NH*NH, + H,O= 2KOH + 2Cr(OH), + 3RH + 3N,, 2K2Cr0, + 3RoNH*NH, + 2H20 = 4KOII + 2Cr(OH), + 3RH + 3N,.

With chromates, this simple reaction is the onIy one which occurs, and practically quantitative yields of hydrocarbon and nitrogen are obtained.

On adding a saturated solution of potassium dichromate to phenyl- hydrazine, a considerable rise of temperature takes place, nitrogen is rapidly evolved with much frothing, and benzene is formed. If the dichromate is in excess, potassium chromate and green chromium hydroxide are produced, whilst i f excess of hydrazine is prenent a strongly alkaline liquid results containing hydrated chromium sesquioxide suspended in it,

Using excess of dichromate and carrying out the oxidation in a nitrometer, a yield of nitrogen amounting to about 92-95 per cent. of the theoretical was obtained. By distilling in s t r am, a similar percentage of the theoretical yield of benzene whs collected, the loss being due mainly to the difficulty of condensing aud separating the whole of the benzer~e from the warder.

No diazo-compound could be defected itmoug t h r products of the reaction, and oa31y a miuuw quantity of H phenol-like substance could be extracted from the filtered alkaliue residue atter acidification. Only

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BY METALLIC OXIDES, PERMANGANATES, AND CHROMATES. 279

very small quantities of diphenyl and azobenzene were formed. The other hydrazines studied behaved similarly.

Potassium chromate alone or in presence of potassium hydroxide does not appreciably oxidise phenylhydrazine a t the ordinary tempera- ture. On heating nearly to boiling, oxidation commences, nitrogen is evolved, and benzene and a very little diphenyl are produced. The action goes on very quietly and regularly, and the yield of benzene and nitrogen is nearly quantitative. It is difficult, however, without special precautions, to retain the whole of the benzene, the vapour of which is carried away by the escaping nitrogen.

As a rule, in a carefully conducted experiment about 75 per cent. of the theoretical yield of pure dry benzene can be obtained. No tar, phenol, or diazo-compound is produced in this oxidation.

The quantitative nature of the reaction is shown better when o- or p-tolyl hydrazine or p-bromophenylhydrazioe is thus oxidised, since in these cases the loss of hydrocarbon or substituted hydro- carbon through volatilisation and imperfect condensation is not so great.

On account of the insolubility of p-bromophenylhydrazine in water, a saturated, aqueous solution of potassium chromate acts much less readily on i t than on unsubstituted phenylhydrazine. Very little action occurs until the liquid boils, but oxidation then proceeds slowly and regularly without the formation of any tar, or of any recognisable quantity of by-products. Nitrogen and bromobenzene are produced in practically theoretical amount, the latter passing over and condensing with the steam ; hydrated chromium sesquioxide separates, and the liquid becomes strongly alkaline from the liberation of potassium hydroxide.

Both the tolyl hydrazines are similarly quantitatively oxidised by a hot saturated, aqueous solution of potassium chromate. Nitrogen, toluene, and a very little ditolyl are formed, and, as before, the chromate is reduced to hydrated chromium sesquioxide and potassium hydroxide.

The oxidation of aromatic hydrazines by potassium chromate is conveniently carried out by dissolving one and a-half times the amount of potassium chromate needed and its own weight of potassium hydroxide in about ten times its weight of water, and adding the hydrazine or its hydrochloride, using, in the latter case, correspondingly more potash. On blowing steam into the mixture, oxidation progresses quietly, the hydrocarbon condenses with the steam, and hydrated chromium sesquioxide separates from the liquid. In a carefully conducted experiment, a practically theoretical yield of hydrocarbon can be obtained.

VOL. XCILI. U*

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280 RICHARDSON : THE REACTION BETWEEN

The author desires to express his thanks to the Government Grant Committee of the Royal Society for a grant which has defrayed much of the cost of this investigation, and to nr. H. B. Baker for so willingly placing the resources of the Christ Church Laboratory a t his service.

CHRIST CHURCH, OXFORD.

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