CHLORINE DERIVATIVES OF PYRIDINE. PART VI. 771 LXVI.- Chlorine Derivatives o f Pyridine. Pa.rt VI. Orientation o f sume Chlorarninop yridines. By W. J. SELL, M.A., F.R.S., and F. W. DOOTSON, M.A. DURING the progress of the work an account of which has been given in this series of papers, a number of chloraminopyridines have been isolated and described, the structural formulae of which are but very incompletely known, These compounds, so far as they have been examined, are remarkably stable, and although the fusing points in some cases do not widely differ yet such considerable variations are exhibited in their reactions that identification is rendered comparatively easy. The compounds dealt with are the trichloro- and tetrachloro-amino- pyridines and as a basis recourse is had to three substances whose structural formulae are known beyond doubt. These are (i) tetrachloro- 2-aminopyridine (Trans., 1898, 73, 779 ; 1900, 77, 235), (ii) tetra- chloro-4-aminopyridine (Arne?..Chern. J., 1886, 6, 377 ; Trans., 1898, 73, 779 ; 1899, 75, 981), (iii) 3 : 4 : 5 : 6-tetrachloropyridine (Trans., 1900, 77, 2), and are thus represented : c1 c1 I. I I. 111. In part I11 of this series of papers (Trans., 1899, 75, 980) a tri- chloraminopyridine was described which resulted from the inter- action of sodium carbonate with a compound containing two pyridine nuclei. Since this trichloraminopyridine on treatment with phos- phorus pentachloride yields a tetrachloraminopyridine identical with I, it follows that the amino-group in the original compound occupies relatively the 2-position and further that in the parent complex the nitrogen of one pyridine nucleus is united to the carbon atom in the 2-position, and not in the 3-position of the other as originally depicted (Zoc.cit.). It is here further shown that the hydrogen atom in this trichloraminopyridine occupies the 6-position by first converting the amino-group into a hydroxyl group in the usual manner and then heating the product at 182O in a sealed tube with phosphorus penta- chloride. The result was a theoretical yield of 3 : 4 : 5 : 6.tetrachloro- pyridine. These changes may be represented thus : c1 c1 c1 c1 Cl/\Cl c -+ CI/\Cl c q c 1 CII,)NH~ H(~)OH H( N ,431 1. i V. V. 111. 3 H 2772 SELL AND DOOTSON: Similar work has been done in the case of the trichloraminopyridine derived from tetrachloroisonicotinic acid by heating the latter with ammonia (Trans., 1897, 71, 1083).From its genesis, the position of the hydrogen atom in this compound is beyond doubt, but with regard to that of the amino-group no experimental evidence was offered, it being merely suggested that from the known mobility of the chlorine atom occupying the position 2, the constitution of the substance was probably represented by the formula : H VI. On heating a quantity of the trichloraminopyridine with phosphorus pentachloride, it was found that a theoretical yield of the tetrachlor- aminopyridine (m. p. 174-175") represented by formula I was ob- tained, thus confirming the original conjecture with regard to it. By the action of ammonia on pentachloropyridine (Trans., 1898,73, 777) two tetrachloraminopyridines have been isolated one of which has been shown to have the constitution represented by formula 11, the other, melting a t 174-175', is identical with I, a structure pointed out at the time as probable, but for which experimental evidence was wanting.From this compound a tetrachlorohydroxypyr- idine was obtained (Zoc. cit.) whose constitution VII is thus established. The two tetrachloraminopyridines mentioned above, on further treat- ment with ammonia and a t a higher temperature, both yield the same trichlorodiaminopyridine (Zoc. cit.) which must therefore be represented by formula VIII. These derivatives are thus represented : c1 c1 NH, NH2 CL/\Cl c Cl(iC1 - Cl/)Cl Cl/)Cl Cl( ,NH2 Cl( ,c1 C1\N/NH2 N N Cl( )OH N VII.I. VIII. 11. It may here be pointed out that the orientation of the compounds represented by formuh IV and VI reduces the trichloraminopyr- idines whose constitutional formulae are still unknown to two in num- ber and in these cases the hydrogen atom must occupy either the 3- or the 5-position. One of these compounds, melting at 144-145O, is mentioned by Anschutz as resulting from the action of phosphorus pentachloride on P-hydroxyglutaramide (Richter's Organische Chentie, Ed. 1899, ii, 573 ; see also Trans., 1900, 77, 235).CHLORINE DERIVATIVES OF PYRIDINE. PART VI. 773 EXPERIMENTAL. ~etrac?doro-2-c6rn~nopyr~d~ne from 3 : 4 : 5-TrichZo?-o-2-aminopyridine. The trichloraminopyridine (m. p. 159-160') derived from the com- pound containing two pyridine nuclei (Trans., 1899, 75, 980) by distillation with sodium carbonate solution, was heated for 4 hours in a sealed tube a t 220-225O with a slight excess of phosphorus penta- chloride, the cold mixture treated with water and distilled with steam, when a quantitative yield of the tetrachloraminopyridine melting a t 174-1 75' (uncorr.) was obtained.On analysis : 0.1481 gave 14.9 C.C. nitrogen a t 19' and 772 mm. N= 11-75, 0.1080 ,, 0.267 AgCl. C1= 61.30. C,H,N,Cl, requires N = 12.06 ; C1= 61.14 per cent. The properties of the compound thus obtained agree with those of tetrachloro-2-aminopyridine (Trans., 1900, 77, 236). Conversion of 3 : 4 ; 5-Trichloro-2-aminopyridine into 3 : 4 : 5-TrichZo~o- Z-?&ydroxypgridine. Five grams of the compound were dissolved by the aid of a gentle heat in 80 C.C.of sulphuric acid containing approximately 80 per cent. of acid. After cooling, rather more than the theoretical quantity of potassium nitrite was added in small quantities a t a time, the mixture heated on the water-bath for half a n hour, with occasional agitation, and then, after cooling, poured into 500 C.C. of water. The new com- pound separated in flocks of fine needles, was filtered off, dissolved in dilute ammonia, to separate any traces of unaltered amino-compound, and again precipitated by the addition of hydrochloric acid. The substance is readily soluble in alcohol, acetic acid, and most organic solvents. When recrystallised from boiling water, it separates on cooling, either in long, filamentous needles, or in flat needles which are quite colourless. On analysis : 0.527 gave 32 C.C.nitrogen a t 15' and 752 mm. N = 7-04. C,H,OCI, requires N = 7.05 per cent. When dissolved in warm, dilute ammonia, the ammonium salt, which is comparatively sparingly soluble in water, separates out on cooling in colourless, satiny, micaceous plates, which rapidly lose ammonia onexposure to air and become opaque. The potassium and sodium salts are much more soluble. The silver salt is thrown down as a jelly by precipitation from t'he ammonium salt.774 CHLORINE DERIVATIVES OF PYRIDINE. PART VI. Conversion of 3 : 4 : 5-TrichZo?.o-2-l~ydrox~p~~idine into 2 : 3 ; 4 : &Tetra- ch Zoropyridine. Two grams of the hydroxy-compound were heated for an hour at 182" with 5 grams of phosphorus oxychloride and twice the theoretical amount of the pentachloride, the mixture treated with water and distilled in a current of steam.The product formed an oil which after the removal of the water solidified during the night. Ex- amination showed that the compound, which melted sharply a t 21-22', mas a pure specimen of 2 : 3 : 4 : 5-tetrachloropyridine. The yield was quantitative. It has been shown (Trans., 1898, 73, 440) that of the three tetrachloropyridines only that in which the chlorine atoms occupy the positions 2 : 3 : 4 : 5 will give a compound with mercuric chloride. On trying the experiment with a dilute alcoholic solution of this product, a semi-solid mass of the double salt was at once obtained, similar in every respect to the known compound. Conversion of 3 ; 5 : 6-TrichZoro-2-aminopyrid~n~ into TetrachZoro-2- aminop yrid ine. The trichloraminopyridine was mixed with phosphorus oxychloride and an excess of pentachloride and heated in a sealed tube for 4 hours at 220-225'. After decomposing the excess of the chlorides of phos- phorus by water, the resulting mixture was distilled in a current of steam and the solid distillate purified by crystallisation from alcohol. The substance melted at 174-175' (uncorr.). The yield was quanti- tative. The following numbers were obtained on analysis : 001258 gave 12.7 C.C. nitrogen a t 16' and 762 mm. N = 12.00. 0.1178 ,, 0.2933 AgCI. Cl=61*40. C,H,N2Cl, requires N = 12.06 ; C1= 61.14 per cent. The properties of the compound thus prepared agree in every respect with those of tetrachloro-2-aminopyridine (Trans,, 1900, 77, 236). UNIVERSITY CHEMICAL IABOKATOKY, CAMBRIDGE.