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denser. Distillation is continued only as long as much substance passes over; during the later stages large needles—mainly the new chloride, P.N.Cl-slowly collect in the condenser. There remain in the flask, besides a strongly acid liquid, a little solid material, consisting partly of phospham, partly of the crystalline acid ammonium tetrametaphosphimate, P.1,0H,(NH4)2, and a considerable amount of oil, which solidifies, on cooling, to a crystalline cake of the compound P.N.Cl, impregnated with an oil of the same empirical composition.
The distillate, consisting of triphospbonitrilic chloride, mixed with about 5 per cent of tetraphosphonitrilic chloride, is dried, and an approximate separation effected by systematic recrystallization from benzene. This solvent has proved the most satisfactory, because the chlorides, in benzene solution, are scarcely affected by water, and no care need be taken to exclude it completely; aqueous ether, on the contrary, acts with considerable ease. The triphosphonitrilic chloride is pure after three or four recrystallizations, the tetraphosphonitrilic chloride accumulating in the mother liquors, the residues from which are again subjected to distillation with steam, the substance remaining in the flask being added to the first residue.
Apart from its influence on the melting point, the presence of very small quantities of the new body in the triphosphonitrilic chloride is. readily detected by dissolving in alcohol-free ether and agitating for several hours with a little water, the tetraphosphonitrilic chloride being indicated by the formation in the water of microscopic needles of the difficultly soluble tetrametaphosphimic acid.
The residue from the distillation with steam is sucked out, whereby most of the oily chloride runs through with the water, and may be collected. The substance is then dried, the tetraphosphonitrilic chloride extracted with benzene and purified by several recrystallizations from this solvent. The residue left by the benzene, treated with dilute ammonia, leaves amorphous substances, and gives up tetrametaphosphimic acid, which is thrown down, on acidifying, as its acid ammonium salt. It may be mentioned here that the affinity of this acid for ammopia is such that its acid salt remains undecomposed even in large excess of hot 10 per cent nitric acid.
The yield of pure chlorides (from 9 kilograms of phosphorus pentachloride) was P3N,C1, 6.9 per cent of the pentachloride, P.N_013, 0.76 per cent of the pentachloride, of which 0.42 per cent was obtained from the residue and 0.34 per cent from the crude steam distillate; these are respectively 12.4 and 1.4 per cent of the theoretical. A further small amount of tetraphosphonitrilic chloride was decomposed during distillation and, in part, recovered as tetrametaphosphimic acid. The yield of oily chloride was not determined, but it was approximately 1 per cent of the pentachloride.
It is not easy to give a reason for the relatively much higher yield of the triple phosphonitrilic chloride. Doubtless more of the quadruple
compound is formed than is actually obtained, which, because of its less volatility, fails to distill over before it is attacked by the ammonium chloride, and I have also mentioned the simultaneous formation of large quantities of chlorides, unacted on by cold, but decomposed by boiling water. Still, it seems that there is some cause leading to the predominant formation and greater stability of this body, perhaps analogous to that acting in the case of the aromatic hydrocarbons. The proof that P2N,C1, is a cyclic compound has not been found, but the occurrence of the number 6 in each case (C. and P3N3) is possibly more than a mere coincidence. Tetraphosphonitrilic chloride is also possessed of great stability, but I have observed, in various connections, that its chlorine is less firmly held than in the triple compound. The reverse appears to be true of the derived acids, P N40,H, being more stable than P2N206H.
Analytical methods.—The analysis of these bodies presents no difficulty. The chlorides, which volatilize on heating, are gently warmed with dilute alcoholic soda or potash. In this solution chlorine is directly determined as silver chloride; phosphorus is determined after evaporating off the alcohol, either by fusing the residue with sodium carbonate or by boiling for one or two hours with strong sulphuric acid, either of which converts it wholly into phosphoric acid. Nitrogen is determined as ammonia after acidifying the saponification product with hydrochloric acid, evaporating the alcohol, and boiling the residue with strong sulphuric acid. Experiment showed that no ammonia is evolved during saponification. In the case of the acids and other nonvolatile derivatives, the alcoholic saponification is omitted and the substance decomposed either by boiling with concentrated sulphuric acid, or fusing with sodium carbonate, the precaution being taken in the latter case first to moisten the mixture in the crucible. Owing to the strong reducing action of the imido group at high temperatures, these substances can not be fused alone in platinum without risk to the crucible. This is true even of the salts, which should give pyro- or metaphosphates on ignition.
The chlorides.—As triphosphonitrilic chloride has been the object of previous investigation, and as I have begun several lines of investigation with the object of explaining its nature and relations, I state here only a few incidental observations.
This chloride, as was early observed, has great crystallizing power. The rhombic crystals have been measured by Miller' and by Groth.? When pure it tends to form large, thick prisms. I have obtained these (from benzene) as much as 8 centimeters long and 2 centimeters wide, their further growth being hindered only by the size of the flask. When impure, it tends to form rhombic or 6-sided plates. It fuses at 114°(corr.), while the quadruple chloride, P, N, Olg, fuses at 123.50 (corr.), but a
1 Jour. Chem. Soc. London (2), Vol. II, p. 227.
mixture of equal parts is liquid below 90°. The corrected boiling point is 256.5° at 760 millimeters pressure. Besides the solvents else where mentioned (for some of which quantitative data are given below), warm glacial acetic acid dissolves it readily. On boiling this solution with zinc dust some phosphuretted hydrogen is evolved. Hot concentrated sulphuric acid dissolves it easily. On boiling, some is decomposed, but the greater part distills off unaltered. The rather pleasant aromatic odor of its vapor has long been known. Although this is by no means irritating, inhaling it in any considerable amount is likely to be followed in two or three hours by alarming difficulty in breathing, succeeded by persistent irritation of the air passages. This insidious property renders care necessary in working with it in large quantities or for extended periods, all the more as the nose is the best instrument for detecting it.
A vapor density determination by Victor Meyer's method at 3600 in dry hydrogen gave 12.35 (calculated 12.01). The volatilization is complete, but on long boiling in air a little solid substance is deposited. Ethyl bromide and sodium are without action on the ethereal solution. Brombenzene and sodium acts slowly on the ether or benzene solution, forming a mixture of brownish amorphous organic substances, in part soluble, in part insoluble in ether, in which only a portion of the chlorine is replaced. No smooth reaction could be obtained.
Zinc ethyl, as observed by Couldridge,' is without action at ordinary temperature. On heating together in a sealed tube a violent reaction occurs, accompanied by liberation of gas and carbonization. If the zinc ethyl be diluted with 2 volumes benzene, a mixture of complex addition products is formed on heating, which are left on evaporating as a no longer soluble white vitreous mass, containing zinc, phosphorus, nitrogen, chlorine, and ethyl. This is decomposed by caustic potash, which liberates a mixture of oily bases of a disagreeable, sweetish odor, which are for the greater part decomposed on distillation, and which dissolve in cold water, and are thrown out on warming. These are slowly decomposed, on heating with hydrochloric acid, into ammonia and what appear to be highly complex phosphinic acids, containing nitrogen. At 170° considerable quantities of combustible gases, and of mono-, di-, and triethyl phosphine are formed by the action of zinc ethyl, in addition to a small amount of a crystalline basic substance containing nitrogen, and showing much the same properties as the oily substances alluded to. The yield was very minute.
Action of water on triphosphonitrilic chloride.—By decomposing chlorophosphuret of nitrogen with aqueous ether, or with alcoholic alkalies, Gladstone obtained a substance which he named deutazophosphoric
1Jour. Chem. Soc. London, Vol. LIII, p. 398.
? Quart. Jour. Chem. Soc. London, Vol. III, pp. 135, 354; Ann. Chem. (Liebig), Vol. LXXVI, p. 70; Vol. LXXVII, p. 315.
3 Jour. Chem. Soc. London, , Vol. II, p. 231.
acid. He afterwards obtained this in larger quantity by treating phosphorus oxychloride with dry ammonia, and assigned to it the formula
and the name pyrophosphodiamic acid. The formation of such an acid can only be due to a deep decomposition of the molecule.
Although unacted on by water alone or by anhydrous ether alone, I have found that a smooth decomposition is easily effected by dissolving the chlorophosphuret in alcohol-free ether, and shaking this solution a long time with water, whereby intimate contact is effected. The final products are hydrochloric acid and an acid in which the chlorine is wholly replaced by oxygen and hydrogen, without further change. I have named this substance, PzN,0.H., trimetaphosphimic acid. If the water contain bases or acetates in solution, the salts are directly obtained. As the acid will be described in a separate section, I mention here only that it is extremely soluble and totally devoid of crystallizing power, but forms some salts of characteristic crystalline form, and bas a strong tendency to form double salts, one of these, P,N,OHNaBa, giving especially fine crystals.
As intermediate products, chlorhydrines have been observed. Theoretically, five of these are possible, one of which I have isolated, namely:
Triphosphonitrilic tetrachlorhydrine, PzN,C10,12.-One part triphosphonitrilic chloride is dissolved in 10 parts alcohol-free ether, and the solution agitated with about one-third its volume of water for six to eight hours, best by means of a small turbine. The water then contains hydrochloric acid and trimetaphosphimic acid, and the ether contains the chlorhydrines and unchanged chloride. The ether is dried over calcium chloride, and the greater part distilled off in the water bath, the latter portions being removed at ordinary temperature by a current of dry air. The residue consists of unchanged chloride, the chlorhydrine in question, and small quantities of others. The greater part of the chloride is removed by a little benzene, and the residual chlorhydrine well washed with carbon disulphide. The yield depends somewhat on the time the water has acted, but as there is a continuous conversion of chloride into chlorhydrine, and of the latter into trimetaphosphimic acid, the amount present at any one time is not great. Under the above conditions it was about 10 per cent of the theoretical, fully one-half the chloride being recovered.
1 According to Monte (Ann. Chom. (Liebig), Vol. CCXLVIII, pp. 241, 244), Gladstone's pyrophospho
PO.OH diamic acid is really NH NH, i.e., dimetaphosphimic acid, which has the same empirical composi.
PO.OR tion as trimetaphosphimic acid. Mento did not obtain his acid from triphosphonitrilio chloride, but from phosphorus oxychloride, and it is not clear that it is really identical with Gladstone's acid from chlorophosphuret of nitrogen. The independent existence and stability of the tetra-acid atfords a presumption that other mombers of the series can exist also.
1, 2, and 3 represent different preparations, 1 having been further parified by recrystallizing from benzene.
The chlorhydrine forms a white sandy powder, consisting of welldefined microscopic prisms. It is very difficultly soluble in boiling benzene, and is insoluble in benzine and in carbon disulphide. With the latter it shows a peculiar behavior. Its refractive index is such that it nearly vanishes and apparently dissolves when brought into the disulphide; on decanting the liquid the moist powder shows beautiful iridescence. Alcohol dissolves it easily and in ether it is much more soluble than the original chloride, the presence of a trace of ether vapor causing it to liquefy instantly. Water dissolves it somewhat slowly, but abundantly, the solution containing hydrochloric acid and trimetaphosphimic acid, the latter being left on rapid evaporation on the water bath or in vacuo, as a transparent, easily soluble, gummy residue. From the aqueous solution of the chlorhydrine, salts of trimetaphosphinic acid were directly prepared and analyzed. The chlorhydrine is quite stable in the air at ordinary temperature,' but on heating at 1000 it slowly increases in weight through absorption of moisture, undergoing decomposition with formation of ammonium chloride. It shows no definite melting point, but, on rapid heating, liquefies imperfectly, gives off hydrochloric acid, and leaves a mixture of amorphous substances of different degrees of solubility in water.
Other chlorhydrines, partly crystalline, appear to be formed simultaneously, but in relatively small amount, and their isolation is attended with difficulties. Whether the 2 chlorine atoms removed are associ. ated with the same or with different phosphorus atoms remains to be determined.
Triphosphonitrilic chloramide, P3N,CL(NH2)2.—The tendency to the formation of stable bodies in which one-third of the chlorine is substituted, observed in the case of the chlorhydrine, appears if triphosphonitrilic chloride be acted on in ether solution by ammonia. Gaseous ammonia may be used, but this is by no means necessary, aqueous ammonia producing the same result. If the chloride be dissolved in ether and
On keeping for several months, a slight formation of ammonium salts was observed.