644 RAY: DIMERCURAMMONIUM NITRITE AND ITS

Nitrite and its Haloid Derivatives.

By PRAFULLA CHANDRA RAY, D.Sc. (Edin.).

SINCE the publication in the Proceedings (1901, 17, 96) of a note on the subject of the present paper, I have, after fuller consideration of the facts, arrived a t somewhat different conclusions from those I had then come t o ; when, therefore, any statement in this paper differs from what is found in that note, it is to be taken as expressing my later view of the matter. The experimental results remain unaltered.

It has already been pointed out by me (Zeit. anorg. Chem., 1896, 12, 365; Trans., 1897, 71, 337) that mercurous nitrite is partly decomposed by water into mercury and a solution of both mercurous and mercuric nitrites, and that when this solution has been prepared by triturating the salt with cold water, about 22 per cent. of the salt dissolves without decomposition." The proportions of the two nitrites

* Ic my paper on mercurous nitrite in the A m a h (1901, 316, 250), it is stated (p. 252) that much the greater part of this salt dissolves in water unchanged ; but that is a clerical error, made in translating. Another error in that paper is the reference (p. 250) to the notice of this salt published by Divers and Haga in the Transactions. The reference to the statement of these chemists about mercurous

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HALOID DERIVATIVES, 645

in solution may therefore be formulated by 4Hg(N02), + (HgNO,),. The addition of sodium chloride precipitates t he mercury of the mer- curous salt and leaves in solution mercuric and sodium nitrites, no doubt as one or more double salts, similar to tha t described recently by Rosenheim (Zeit. ccnorg. Chem., 1901, 28, 171). It is probable tha t the solution of the two mercury nitrites contains them as double salts also, mercuric-mercurous nitrites, firstly, because neither of the two is obtainable in solution by itself; secondly, because mercurous nitrite dissolving in a solution of sodium or potassium nitrite is wholly decomposed into metal and mercuric nitrite combined with the alkali nitrite, and, thirdly, because, as pointed out inearlier papers, the solu- tion of the mixed nitrites is neutral to litmus, whereas even mercuric chloride is acid in absence of an alkali chloride. On the other hand, however, it should be mentioned that during the spontaneous evapora- tion of this solution, hydrated mercurous nitrite crystallises out (Trans., 1897, 71, 340). The non-acidity of these mercuric-mercurous nitrite and mercuric-sodium nitrite solutions, as well as their stability on dilution, distinguishes them from that of either of the mercury nitrates, and other differences are to be found in their behaviour with urea and with sodium sulphate, neither of which precipitates them (Trans., 1897, 71, 1103).

Feeling that the formation of stable and neutral double salts of mercuric nitrite gives support to the view tha t nitrites have a consti- tution allied to tha t of haloid salts, as distinct from tha t of oxylic salts such as the nitrates, it occurred to me that further insight into the matter might be gained by a study of the action of ammonia on mercuric-sodium nitrite. A mmonia yields with the mercuric-sodium nitrite solution an insoluble compound having the composition ex- pressed by the formula NHg2N02, together with a little less than balE a mol. of water, of which it is partly deprived when exposed in a desiccator; it is slightly decomposed in the steam-oven, Since mercuric nitrate, similarly treated, gives also a somewhat hydrated precipitate, NHg2N0,, which, according to Pesci, becomes anhydrous when thoroughly washed with boiling water, a treatment hardly possible in the case of the nitrite, the composition of the ammoniated nitrite fails to throw the expected light on the consti- tution of nitrites.

The ammoniated mercuric nitrite and its haloid derivatives have, however, a special interest in the support they afford to the dimercur- ammonium theory propounded by Rammelsberg in 1888 (J. pr. Chem., [ ii], 38, 558), and since extended to all ammoniated mercury com-

nitrite is also erroneously given in the footnote to my paper on this salt in the Transactions (1897, 71, 337). In both cases it should have been to Prcc., 1886, 2, 250, and Trans., 1887, 51, 49.

VOL. LXXXI. x x

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646 RAY : DIMERCURAMMONIUM NITRITE A N D ITS

pounds by Pesci (Gazxetta, 1890, 19, 509, and 20, 485). The anhydrous nitrate is known (Rammelsberg, Pesci), and the anhydrous bromide (Pesci), as well as the impure anhydrous chloride (Wehl, Rammelsberg), but in the rest of the ammoniated mercury compounds the dimercurammonium salt assumed to be present is so either in combination with water, or with ammonium salt, or with mercury salt. The double salts, however, behave in every respect as such (Rammelsberg, Pesci), familiar instances of which are the two ‘ white precipitates,’ NHg,Cl,NH,Cl and NHg2C1,3NH,Cl. But hydrated di- mercurammonium salts-Millon’s, or oxydimercurammonium, salts- do not yield water until the salt itself decomposes. This water is, however, readily displaceable by ammonium salts (Pesci, Andre, and others), whilst its fixity to heat before decomposition of the salt may be no more than what is seen in the like behaviour of hydrated aluminium chloride, hydrated magnesium chloride, and many other salts. K. A. Hofmann and Marburg, it is true, deny the existence of dimercurammonium salts (Annalen, 1899, 305, l g l ) , but Pesci’s reply to them (Zeit. anorg. Chem., 1899, 21, 361) is an experimental refut,a- tion of most of their objections.

Now, the ammoniated nitrite, having a t most only half the hydra- tion necessary to constitute the oxydimercurammonium nitrite, must be at least half dimercurammonium salt. Not only is this the case, but it has yielded me, in a way to be described presently, a dimercur- ammonium chloride and a bromide, each also with only half the hydra- tion demanded by the oxydimercurammonium constitution. Finally, this half mol. of water can seemingly be displaced by a half mol. of either mercuric bromide or chloride. The half-hydrated dimercur- ammonium chloride had already been obtained by Andre in 1889 (Conzpt. rend., 108, 1164), although unknown to me when I was examining it. Andre’s method of getting it is perfectly definite, and consists in treating mercuric chloride in dilute solution with ammonia equivalent to one-fourth of its chlorine in presence of potassium hydr- oxide equivalent t o the rest, thus ensuring the non-formation of any ammonium chloride. My success was gained in essentially the same way, for I had present only just enough ammonia to supply the nitrogen of the dimercurammonium. Having prepared from the ammoniated nitrite the new double mercuric-ammonium salts, 2HgCI,,NH4C1 and 2HgBr2,NH,Br, I treated them each with potassium hydroxide, and in this way secured the conditions P have mentioned. Theinteraction occurs according to the equation :

2(2€IgCl,,NH4Cl) + 8KOH = 2NHg,Cl,H20 + 8KCl + 7H20,

as I proved by finding always four-fifths of the chlorine in the mother liquor. By using a little less potash, I have sometimes succeeded in

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HALOID DERIVATIVES. 647

getting the salt 2NHg2Br,HgBr,, and, in an impure state, 2NHg2Cl,HgCl,, which salts, it is evident, can only be written down as dimercurammonium compounds.

E XP E R I M ENTAL.

Dimercummmonium Nit~ite.-In order to prepare this salt, mercurous nitrite is acted on by water so as t o obtain a solution of mercuric- mercurous nitrite, which is then changed to one of mercuric-sodium nitrite by careful addition of just enough sodium chloride. As in the case of silver nitrate and sodium chloride, the end point is hard to hit off, and with every care a minute but unimportant quantity of either mercurous salt or of chloride must be left in solution. Another and better way of preparing mercuric-sodium nitrite solution is to dissolve mercurous nitrite in a concentrated solution of sodium nitrite, when half the mercury separates as metal ; but with this I only became well acquainted too late for use in the work of this paper. Solutions of mercuric-sodium nitrite can also be prepared by adding either mercuric (Rosenheim) or mercurous nitrate t o sodium nitrite solution, but these, of course, contain sodium nitrate, whicb, for this investigation, would be an undesirable, although probably inactive, constituent of the solution, To the mercuric-sodium nitrite solution, filtered from the mercurous chloride, dilute ammonia is gradually added until in slight excess. A cream-coloured, flocculent, but somewhat dense precipitate is produced, which is washed on a filter by aid of the suction-pump. Being slightly decomposed in the steam-oven, i t has to be dried over sulphuric acid, and as it then collects into compact lumps, these are broken up and again exposed in the desiccator in order to facilitate the drying.

Nitrogen was determined by combustion with oxide of copper and chromate of lead. Although the analyses of the salt are not sufficient to decide the point, there is strong presumption in favour of the salt being anhydrous, as there is no guarantee that all moisture was removed from the preparations analysed :

The dry salt is pale yellow.

Mercury. Nitrogen.

84.13 5.99 84.64 6.02 84.87 5.92 85.30 6.00 85.94 - 86-02 -

2NHg2N0,,H20 requires ................ 83.68 5.85

.......................................

NHg2N02 requires ..................... 86.96 6-08

x x 2

I Found

When heated in a bulbtube, the salt decomposes without fusing,

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648 RAY: DIMERCURAMMONIUM NITRITE AND ITS

giving off nitrous fumes, mercury, and water, and leaving a yellowish residue, mostly mercuric oxide.

Hofmann and Marburg find that ' infusible white precipitate ' yields the whole of its nitrogen as ammonia when i t is heated at 130" for half-an-hour or more with a 20 per cent. solution of potassium hydr- oxide. I have repeated their experiments and can confirm their experience, having obtained 5.36 per cent., calculation giving 5.57. Dimercurammonium nitrite, however, could not be made to yield more than 2.5 per cent. of nitrogen by this treatment, whilst theory requires 3 per cent.

New Mercuric Ammonium Chloride cmd Bromide.-Like other salts of its kind, dimercurammonium nitrite dissolves readily in warm hydrochloric acid or hydrobromic acid; nitrous fumes escape, and the solution leaves, when evaporated, a white, crystalline mass which volatilises slowly, even on the water-bath. It proves to be a new mercury and ammonium salt, chloride, or bromide, according to the acid used, having the composition shown by the formula 2HgCl,,NH4C1 or 2HgBr,,NH,Br. The double chloride fuses and sublimes at a gentle heat, and is very soluble in water. The double bromide is decomposed by water into its constituent salts, and when the sparingly soluble mercuric bromide has been dissolved again by stirring it with the boiling solution of ammonium bromide, it separates as the solution cools in white, nacreous crystals. The presence of free acid seems to be necessary for the formation of these double salts, and I have, in fact, been able to prepare the double bromide by dissolving the single salts in the indicated proportions in presence of hydrobromic acid and evaporating the solution, but I have not succeeded in a similar way in getting the double chloride. The double bromide forms prisms and tablets, probably triclinic. The results of analyses of the two double salts are as follows :

Mercury. Chlorine. Nitrogen. Calc. for 2HgCl,,NH4Cl ...... 67.17 29-81 2.35 Found ........................... 67.92 29.00 1.96

29.42 - - ,, ........................... 67.94 29.20

............................. 67.20 Mercury. Bromine. Nitrogen.

Calc. for 2HgBr,,NH,Br ...... 48*90 48.90 1.71 Found ........................... 49.29 48-31 1.66

- ,, .......................... 49.38 47-86 ............................. 48-65 - -

Production of Dime~wwamrnonniurn Chloride and Bromide from ths above-described Double #ah.-When the double chloride is stirred with excess of dilute solution of potassium hydroxide, it gives a pale yellow precipitate having the composition of, and being apparently

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HALOID DERIVATIVES. 649

identical with, Andre's half-hydrated dimercurammonium chloride, 2NHg2CI,H20, according to the results of analysis, which were :

Mercury. Chlorine. Nitrogen. Calc .................................. 87-25 7-74 3.05 Found .............................. 87-10 7.54 2.90

- - ,, .............................. 87-94 ,, .............................. 87.06 - -

Jt may be heated to 150° without appreciably losing water. The filtrate from this precipitate contains exactly four-fifths of the chlorine of the double salt ; found : 24.10 and 23.98, instead of 23.85 = 4/5 of 29.81 per cent.

When treated with excess of potassium hydroxide, the double bromide yields a deep red precipitate which has the composition expressed by 2NHg2Br,H20, after drying at 100'. There is left in the filtrate 39 per cent. of the bromine of the double salt, which is 415 of the total, 48.9. Analysis of the precipitate gave :

Mercury. Bromine. Nitrogen. Calc. .............................. 79.52 15.91 2-78 Found ........................... 79.82 15.66 2-60

), ........................... 79.97 16.10 2.54

New Mercuric-ammonium Chlorobomide,--When dimercurammonium bromide is dissolved in hydrochloric acid and the solution concentrated, the double salt, 2 E€gCl,,NH,Br, is obtained. Dimercurammonium bromide is re-obtained quantitatively by mixing this salt in solution with excess of dilute potassium hydroxide, all the chlorine, and no bromine, remaining in solution. Thus, 22.37 and 23.02 per cent. of chlorine were found in solution instead of 22.19, given in the subjoined table :

Mercury. Chlorine. Bromine. Nitrogen. Calc. ............... 62.50 22.19 12.50 2.1 9 Found ............ 63.01 20.89 12.71 1.97

- - - ,, ............ 63.5 ,, ............ 62-89 I - -

It is somewhat remarkable that the compound dimercurammonium chloride, when dissolved in hydrobromic acid and the solution con- centrated, does not yield the bromochloride, 2HgBr,,NH4Cl, but the double bromide, 2HgBr2,NH4Br ; in other words, the chlorine is re- placed by bromine. This reaction has its analogy in Field's experiment (Trans., 1858, 11, 234).

Dirnerclurarnmoniu~zcm-mercuric Bromide and Chloride.--By adding potassium hydroxide, gradually and not in excess, to a boiling solution of the double bromide of mercury and ammonium, I have obtained the

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650 MORGAN: INFLUENCE OF SUBSTITUTION ON THE

saIt 2NHg2Br,HgBr2, which is, however, not always easy to get. The analyses of three distinct preparations are given below :

Mercury. Bromine. Nitrogen. Calc. .............................. 74.19 23.74 2-07 Found ........................... 73.55 24.30 2-35

,) 22.82 - ........................... 72-65 )) ........................... 73.44 21.99

I have not succeeded in getting the corresponding chloride in a pure state, but a yellowish-white precipitate, which can hardly be anything else but impure dimercurammonium-mercuric chloride, is obtained when, to a dilute solution of the mercuric-ammonium chloride, above described, potassium hydroxide is very gradually added with care, t o avoid using it in excess. The calculated percentage composition of 2NHg2C1,HgC12 is mercury, 8 5 5 ; chlorine, 12.1 ; and nitrogen, 2.4, whilst the mean numbers of some half-dozen fairly concordant analyses of as many different preparations of this precipitate are, respectively, 84.5, 11.3, and 3.0. The same numbers would express the percentage cornposition of the following mixture, which, it will be seen, consists mainly of dirnercuremmonium-mercuric chloride, 2NHg2Cl,~HgC12 + QNH,Cl+ $H20.

I n conclusion, I wish to express most cordial thanks to Professor Edward Divers, E.R.S., for some valuable suggestions, which have greatly aided me in putting this paper together.

CHXMICAL LABORATORY, PRESIDENCY COLLEGE,

CALCUTTA.

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