CHARLES A. KRAUS Brown University, Providence, Rhode Island
TIME
vas, before the Hatchet Men-commonly known as "Referees7'-had usurped editorial functions, when an author could introduce into his paper many interesting and useful hits of information even though they had little hearing on the main theme of the paper. Thus, much useful information was conserved to he used later by other investigators while, a t t,he same time, the paper was usually enlivened thereby. Indeed, such information often stimulated others to undertake researches which, otherwise, they would not have begun. Today, all this has been changed; everything not having a direct hearing on the problem in hand is eliminated. The final paper gives one the impression that nothing has been left undone, and that there is nothing more that need be done. Such papers are not very iuspiring. It would seem that all the red meat has been trimmed off the literary roast and all that remains is
1.
bone and fat and gristle. And, when a paper is puhlished, the introduction and discussion are printed in large type while the data, if appearing a t all, and pertinent experimental details appear in type so small that it requires microfilm equipment to read it. Is this not a case of the horse pushing the cart? The most important element in a paper is the result presented in the form of data along with an evaluation of their precision. On the basis of considerations such as these, this author has been led to publish some fragments of chernistry, chiefly in the way of observations which have been accumulated over the years and which have been touched upon only briefly in earlier papers or, otherwise, have been left unreported. The brief sketches which follow are, for the most part, undocumented. On request, the author would he glad to supply such further information as he may have.
REACTION O F POTASSIUM AMIDE WITH ALIPHATIC POLYHALIDES IN LIQUID AMMONIA1
P~TASSIUM amide is a moderately
strong electrolyte and is verv soluble in liauid ammonia. I t is an ammono base and, in liquid ammonia, reacts in a manner similar to that of potassium hydroxide in water. However, the amide ion is much less strongly electronegative than is the hydroxyl ion and, therefore, we frequently find it acting as a reducing agent. Thus, potassium amide is oxidized to potassium hydroxide and potassium nitrite by molecular oxygen in liquid ammonia. The solid is likewise oxidized by oxygen hut, unless the oxygen pressure is kept very low, the reaction takes place explosively. With an alkyl halide, potassium amide reacts according t o the equation:
HCCI,
- +KNH,
HC(NH,),
-NH,
+KNHI HCN ---KCN I (2)
When we come to carbon tetrachloride and hexachloroethane, complex and deep-seated reactions take place which cannot be described in terms of Franklin's ammonia system which involves substitution of NH2 for chlorine and subsequent deammoniation of the product. ( 1 ) Carbon Tetrachloride. According to Franklin's system, we should expect a salt of cyanamide NCNHe, or some related substance, as end product of reaction. Actually, the observed results of reaction are as followsi ( a ) 90 per cent of the carhon appears as potassium cyanide. (b) Nitrogen is evolved, the ratio of nitrogen atoms to mols of cyanide being in the proportion of 2:3. (c) Hydrogen is evolved along with the nitrogen in The reaction is quantitative and rapid. Actually, of the proportion of one atom of hydrogen . . - to three atoms course, it is the amide ion that reacts; however, for the of nitrogen. sake of simplicity, will be written in molec. . equations . (d) The ratio of chloride to cyanide is 4.5: 1. ular form. (e) The ratio of mols of amide to mols of tetrachloride The reactions of methylene halides seem not to have reacted is sli~htlv than five (5.25). " xreater , , been investieated. Chloroform and notassium amide The principal product of reaction is potassium cyareact in the sense of Franklin's "ammonia system of nide. The CN/N ratio of 3:2 is doubtless significant. chemistry" potassium cyanide being formed quantita- The principal reaction might he written: tively. The reaction may be formulated somewhat as
-
-
fnllnws: . -. .... . . 1 The observations which follow were accumulated by Dr. 1931Norman L. Cox in the Brawn Laboratories during the 33; they have not been reported heretofore.
3CClr
+ 15KNHz = 12KCI + 3XCN + N? + 10NHa
(3)
The nitrogen must be formed at some stage of the deammoniation process; potassium cyanamide is a stable, difficultlysoluble compound. In all likelihood, the hy-
JULY, 1952
drogen is formed in reactions that involve the 10 per cent of carbon that does not form cyanide. The excess amide is probably involved in these side reactions. (2) Herachloroethane. If hexachloroethane reacted according to Franklin's ammonia system, we should expect cyanogen as end product. Actually, a deep-seated reaction takes place which results in the complete destruction of the hexachloride molecule. Although difficultly soluble in liquid ammonia, the hexachloride when finely divided, reacts readily with potassium amide. Observations are as follows: (a) When reaction is completed, the evolution of gases ceases and the solution has a pale yellow color. Presently, the color darkens and, in the course of 10 to 20 minutes, carbon precipitates. Approximately 60 per cent of the total carbon appears as free carbon. The residue in the tube consists of carbon and potassium chloride and the weight of the contents of the reaction tube is less than that of the reactants. (b) The gas collected during reaction is nitrogen. Somewhat less than one atom of nitrogen is obtained per atom of precipitated carbon. (c) A volatile carbon compound is produced which decomposes as it is carried into water in collecting the evolved gases. Flashes of light appear in the collecting tube as the bubbles of gas, largely ammonia, collapse. A scum of carbon forms on the surface of the water in the collecting tube. (d) I n one experiment, the ammonia was taken off at low temperatures; when the tube was allowed to warm up there was a mild detonation accompanied by a flash of light and carbon was deposited on the interior walls of the reaction tube. In this case, there were no flashes in the absorption tube and no carbon appeared on the surface ofthe water in the collecting tube.
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The reaction of hexachloroethane with potassium amide is deep-seated anbcomplex. It seems likely that the evolved nitrogen is due to the decomposition of some compound which leaves free carbon, on the one hand, and produces nitrogen, on the other. Roughly 35 to 40 per cent of the total carbon forms an unstable compound mhich is fairly volatile. It decomposes in the collecting tube to form carbon and, perhaps, nitrogen. No other gas appears. This compound appears to be unstable a t room t,emperat,nroand decomposes explosively. The above reactions serve to illustrate how little we know about the chemistry of liquid ammonia and how greatly it differs from that of other solvents. It would be of interest t o know what would be the reaction of potassium amide with highly halogenated derivatives of aliphatics containing more than two carbon atoms per chain. It would also be of interest to know what reactions might occur in the case of highly halogenated aromatics, particularly hexachlorohmzene. Solutions of the alkali metals in liquid ammonia are much more powerful reducing agents than is potassium amide. However, in order to be able to interpret such reduction reactions, we need to have some knowledge of the reaction of the amides. In the reaction of the metals with alkyl halides, the metal amide is formed which, in turn, reacts with the halide to form amine. Thus, sodium reacts with methyliodide to give a quantitative yield of methane and methylamine in equimolar proportions. We know nothing about the reactions of alkali metals with polyhalides. A study of such reactions might throw much light on react,ions such as t,hose out,lined above.
