POSITIVE HALOGEN I N ORGANIC COMPOUNDS.
991
at %omconcentrations. The general conclusions of the paper are not affected. The most general expression for the first differential coefficient is
At low concentrations the A,CA-curve will cut the A-axis a t an angle I
whose tangent is equal to - -,.
At higher concentrations the tangent to
K
the curve will decrease because of the increase in the value of K', as well as
. The curve will, d(CA) therefore, be convex toward the C-axis in dilute solutions. It is not possible to follow up the form of this curve readily a t highe; concentrations without introducing the equation for the conductance function. If the function XIV i s introduced, we have the equation the increase in the value of the term involving I
So long as m C
I.
-
d A will always have a negative value whish ded(CA)
creases with increasing concentration. When m
>
dA will pass d(C@ through zero and thereafter become positive a t higher concentrations, which corresponds with the form of conductance curves such as we have them in solvents of low dielectric constant. C. A. KRAUS. I,
_ l _ _ l
WORCESTEE,MASS
~CONTEIBLITIONFROM THE CHEMICAL LABORATORY OF THE UNIVERSITY OF
ILLINOIS. 1
OSITIVE HALOGEN IN ORGANIC COMPOUNDS. IODINE IN DT-IODOACETYLENE AND CHLORO-IODO-ETHYLENE.' BY LLOYDB. HOWELL,WITH WILLIAMA. NOYES. Received February 3, 1920.
For a number of years chemists have recognized the fact that certain organic halogen compounds, e. g., those in which a halogen has replaced a hydrogen atom of any of the groups: -NH2, > N H , or -OH, exhibit extraordinary activity. Unlike the halogen of the ordinary types of alkyl and acyl halide linkage, which are reduced with more or less difficulty, the halogen of the above-rnentioned types shows actual oxidizing power in the presence of such reducing agents as aqueous solutions of ferrous An abstract of a thesis submitted by Mr. Howell in partial fulfilment of the requirements for the Degree of Doctor of Philosophy in the Graduate School of the TJiniversity of Tllinois.
LLOYD B. €%OWELLWITH WILLL4M A. NQUES.
992
salts or metallic iodides. In addition to this exceptional property such compounds as a rule are unstable when isolated and many decompose with explosive violence. These peculiar properties have so far not been satisfactorily explained. Inorganic halogen compounds which are similarly unstable and of oxidizing properties are the halogenated ammonias, nitrogen tricnlori le and nitrogen iodide. The work of Chattaway,' Orton, W. A. FSoye~,~ and others with these compounds has led to a satisfactory explanation of their behavior by the assumption that the halogen is combined as a positive atom and not negatively as in ordinary chlorides, bromides and iodides. Certainly no more reasonable explanation has so far been advanced. It was our purpose in this investigation to determine whether or not a similar explanation might be made for the behavior of certain halogen derivatives of acetylene. In addition to the types of linkage mentioned above we have the C - X linkage which gives relative instability to the molecule and, it will be shown, possesses oxidizing properties. Just as for many cases in the groups -NHt, > NH, and -OH the hydrogen atom may be replaced by either metals or halogen, so in acetylene or the monosubstituted acetylenes we have hydrogen replaceable by either metals or halogen. And since both the original hydrogen atom of acetylene and the metal of the acetylides or carbides are undoubtedly positive, i t would seem a reasonable inference that the chlorine of chloro-acetylene and dichloro-acetylene, the bromine of bromo-acetylene and dibroma-ace tylene, and the iodine of iodo-acetylene and di-iodo-acetylene are likewise of a positive nature. Since it is relatively the most stable of the 6 known halogen substituted acetylenes and the easiest of preparation, di-iodo-a cetylene has been investigated first for those properties which might indicate the nature of the =C!-hal. linkage. Certain of the properties of this compound attributed by NefS t o the existence of bivalent carbon in the molecule are better explained by the assumption that the iodine atoms are positive in nature and the carbon quadrivalent. Bi-iodo-acetylene when warmed with a neutral or faintly acid solution of potassium iodide or simply allowed to remain suspended in such a solution for a short time liberates free iodine and acetylene is regenerated. The rate of the reaction is very slow unless an excess of potassium iodide i s present and a trace of acid added to neutralize the alkali formed in the reaction I - Q: zz C -- I 2HOH 2KI H - C G-- H zKOH$ 212. If the iodine be taken up by titration with sodium thiosulfate it is es-
+
3
a
+
+
J. Chew. Soc., 70, 1572 (1896);Ant. Cheri. J., 23,363 (1900);24, 139 (1900). TElrS JOURNAL, 2% 460 (1901);35, 767 (1913); 39, 90.5 {1917), Avn.,_298, !343j(1W7).
POSITIVE: HALOGEN IN ORGANIC COMPOUNDS.
9Q3
pecially noticeable that the end-point of the titration is very indistinct, more iodine being liberated almost instantly as the equilibrium is displaced. It is difficult t o adopt any explanation €or this reaction other than that both iodine atoms of di-iodo-ac~tyleneare strongly electro positive and capable of taking up 2 electrons each. That dibromo-acetylene and dichloro-acetylene recently prepared and described. by Boeseken and Carrierel would show the same reaction even more markedly would be predicted from their relatively more unstable character. Experiments to test out these predictions are now in progress. As a further indication of the positive character of the iodine atoms of di-iodo-ace1ylene, attempts have been made, first, to prepare it by means of iodine monochloride and, second, to prepare nitrogen iodide from diisdo-acetylene by the action of ammonia. Since iodine monochloride and ~ ~ j t ~ oiodide ~ e nare both compounds containing positive iodine these reactions would furnish considerable evidence in the matter. Iodine monochloride, however, as is well known, reacts by addition upon acetylene itself and this has been found to occur both in and out of solvents. The product always obtained i s I -chloro-2-iodo-ethylene as first shown by Plimpton.2 The action of iodine monochloride upon metallo derivatives of acetylene however yields better results, Iodine monochloride with calcium carbide and with copper acetylide forms diiod 0-acetylene zIC1 CaCz -+ G I E C4: CaCh e
+ -+ 2ICl + cu2c2 + CL = G I + CuzCl*.
The reduction of di-iodo-acetylene by ammonia has not been accomplished. The reaction has been tried out in aqueous and in ether solution and in the absence of any solvent, employing liquid ammonia itself (in which di-iodo-acetylene is readily soluble). The conditions of tempera- , ture and of pressure were likewise varied but in no ease could nitrogen iodide be isolated as a product, although the formation of traces of acetylene could be shown. This result might be predicted, however, since it has recently been shown by Datta and Prosada that nitrogen iodide is an exexdent iodinating agent for acetylene and gives practically quantitative yields of tetra-iodo-ethylene. This reaction would thus seem to be only slightly reversible. In his well-known arLicle on “Die Chemie des Methylens,” Nef4 has drawn the conclusion that di-ido-acetylene and iodo-acetylene and the 1
Verslag Akad. W&enschappen, Am~terdanz,22, ~186-88 (19~4); C. A . 8, 3296
( 1 0 1 4).
2
J. Chem, SOL,41. 392 (1882) 391 451 (191 1, Loc, ckt.
’ TBKS JOURNAL,
4
LLOYD B. HOWELL WITH WILLIAM A . NOYES.
993
other halogen substituted acetylenes must possess the acetylidene structures :
'>==e< 1
Hl)c==c
B
That is, the positive nature of the halogen atom as shown by its tendency to become trivalent might account for the formation of iodobromides as well as for the production of an iodochloride. In fact it is not entirely improbable that the compound C&Br2, assumed by Professor Nef to be unsymmetrical, Br
is in fact the compound,
c-c
/I
Br
formed as a secondary or rearrangement product of the first reaction given above. The explanation for the formation of I>C I= (. e1
Cl
as a secondary or rearrangement product in the chlorination of di-iodoacetylene as given below is an analogous case. The poisonous character, disagreeable odor and irritating effects of the vapor of di-iodo-acetylene attributed by Nef to the presence of dyad carbon may possibly be due to positive or unsaturated iodine. The markedly poisonous character of the compourids nitrogen trichloride and nitrogen tri-iodide ammonia is well known. Moreover if we were to admit the coinpound CzIz to be di-iodoacetylidene, the structure of the iodochloride (described below) formed by the action of chlorisarl: ~ q $ tbe +
c1
c'?i 7 1
c1 ;
- - c
