On the Formation of Hydrazodicarbonamide from Semicarbazide Hydrochloride
Abstract Generated abstract
This paper examines the unexpected formation of hydrazodicarbonamide during heating of semicarbazide hydrochloride under conditions related to Zelinsky’s reagent. The authors identify the crystalline product by elemental analysis, melting behavior, and oxidation to azodicarbonamide, then compare reactions in aqueous solution with acetic acid, disodium phosphate, carbonate, and mixtures of free semicarbazide and its hydrochloride. The experiments show that hydrazodicarbonamide can form at 100°C in water, especially when both semicarbazide and its salt are present, but not in strongly alkaline solution. The authors argue that the reaction proceeds through splitting off hydrazine as a salt, with hydrolysis and salt formation governing whether the condensation advances.
Full Text
Prof. Ya. I. Mikhailenko and scientific associate A. M. Chernukhin
On the question of the formation of hydrazodicarbonamide from semicarbazide hydrochloride
(From the Laboratory of Organic Chemistry of the Tomsk Technological Institute.)
When applying Professor Zelinsky’s reagent1 of the composition 20 g
$\mathrm{NH_2.CO.NH.NH_2.HCl} + 20$ g $\mathrm{CH_3COOK} + 60$ g water, upon heating there was observed the separation of a white crystalline substance, sparingly soluble in water and completely insoluble in ordinary organic solvents. After purification by recrystallization from water, this substance was subjected to elementary analysis. The composition of the substance was expressed by the following figures:
| C | H | N | O |
|---|---|---|---|
| 22.00% | 5.28% | 46.83% | 25.79% (by difference) |
Melting point: 243°C. Melting is accompanied by decomposition.
This composition and melting point correspond very closely to so-called hydrazodicarbonamide:
\[ \mathrm{NH_2.CO.NH.NH.CO.NH_2}, \]
whose composition is expressed by the following figures:
| C | H | N | O |
|---|---|---|---|
| 21.43% | 5.35% | 46.43% | 26.79% |
and which melts at 246°C with decomposition.
The identity of the substance found with hydrazodicarbonamide was, moreover, proved by oxidizing it with a chromic mixture, whereby an orange-red substance was formed, i.e. azodicarbonamide:
\[ \mathrm{NH_2.CO.N{=}N.CO.NH_2} \]
according to the equation:
\[ \mathrm{NH_2.CO.NH{-}NH.CO.NH_2 + O = NH_2.CO.N{=}N.CO.NH_2 + H_2O.} \]
The reaction of formation of hydrazodicarbonamide under the conditions of the experiment in question could proceed only according to the following equation:
\[ \mathrm{ H_2N.CO.NH.NH_2.HCl + HCl.H_2N.NH.CO.NH_2 = } \]
\[ \mathrm{ H_2N.CO.NH.NH.CO.NH_2 + HCl.NH_2.NH_2.HCl } \]
i.e. with the liberation of a molecule of hydrazine hydrochloride from two molecules of semicarbazide.
Reactions analogous to the one given above, namely those proceeding with the splitting off of ammonia in the form of an ammonium salt or in the form of free ammonia from two molecules of an amine, are known, for example:
\[ \mathrm{C_6H_5.NH\boxed{H + C_6H_5.NH_3Cl} = C_6H_5.NH.C_6H_5 + NH_4Cl} \]
\[ \mathrm{NH_2.CO.NH\boxed{H + NH_2}.CO.NH_2 = H_2N.CO.NH.CO.NH_2 + NH_3} \]
In this way Curtius\(^1\) succeeded in obtaining hydrazodicarbonamide itself by heating semicarbazide:
\[ \mathrm{NH_2.CO.NH.NH\boxed{H + NH_2.NH}.CO.NH_2 =} \]
\[ \mathrm{NH_2.CO.NH.NH.CO.NH + H_2N.NH_2} \]
But all these reactions proceed at high temperature. Thus, the first reaction (formation of diphenylamine) proceeds at \(220^\circ\)—\(239^\circ\); the second (formation of biuret)—at \(150^\circ\)—\(170^\circ\); the third (formation of hydrazodicarbonamide) at \(130^\circ\)—\(150^\circ\).
In our case the reaction of splitting off hydrazine from two substituted hydrazines with subsequent synthesis of the residues proceeds at a comparatively low temperature and, moreover, in aqueous solution. This is an exceptional case, and therefore it seemed interesting to investigate more closely the conditions under which this splitting off occurs.
For this purpose we carried out the following series of experiments.
Experiment I.
Taken:
\[ \begin{aligned} &0.5\ \mathrm{gr.} && \mathrm{NH_2.CO.NH.NH_2.HCl.}\\ &0.5\ \text{“} && \mathrm{CH_3.COOH.}\\ &1.5\ \text{“} && \text{water.} \end{aligned} \]
After heating this solution for 6 hours at a temperature of \(100^\circ\mathrm{C}\), \(0.17\ \mathrm{gr.}\) of hydrazodicarbonamide separated. The next 6 hours gave \(0.04\ \mathrm{gr.}\), and, finally, after another 6 hours, a further \(0.02\ \mathrm{gr.}\) was obtained. Further heating, although accompanied by separation of hydrazodicarbonamide, did so only in insignificant quantities.
Thus, over the course of 18 hours, at \(100^\circ\mathrm{C}\), \(0.23\ \mathrm{gr.}\) of hydrazodicarbonamide separated. This amounts to about \(86\%\) of the theoretical yield.
Experiment II.
Taken:
\[ \begin{aligned} &0.5\ \mathrm{gr.} && \mathrm{NH_2.CO.NH.NH_2.HCl}\\ &0.4\ \text{“} && \mathrm{Na_2HPO_4.12H_2O}\\ &2.0\ \text{“} && \text{water} \end{aligned} \]
Under conditions entirely analogous to those of the preceding experiment, \(0.21\ \mathrm{gr.}\) of hydrazodicarbonamide separated over the course of 18 hours. This amounts to approximately \(80\%\) of the theoretical yield.
Experiment III.
Taken:
\[ \begin{aligned} &0.5\ \mathrm{gr.} && \mathrm{NH_2.CO.NH.NH_2.HCl}\\ &2.0\ \text{“} && \text{water} \end{aligned} \]
\(^1\) Ber. 27, 57.
Heating was carried out at \(100^\circ\). The separation of hydrazodicarbonamide did occur, but comparatively slowly, approximately twice as slowly; \(0.21\) g of hydrazodicarbonamide was formed only over the course of 36 hours.
Experiment IV.
Taken:
\[ \begin{array}{rcl} 0.5\ \text{g} & \ldots & \mathrm{NH_2.CO.NH.NH_2.HCl}\\ 1.00\ \text{''} & \ldots & \mathrm{Na_2CO_3.10H_2O}\\ 2.00\ \text{''} & \ldots & \text{water} \end{array} \]
Under experimental conditions analogous to the preceding ones, no formation of hydrazodicarbonamide was observed.
Experiment V.
Taken:
\[ \begin{array}{rcl} 1.0\ \text{g} & \ldots & \mathrm{NH_2.CO.NH.NH_2.HCl}\\ 0.23\ \text{''} & \ldots & \mathrm{Na_2CO_3}\ \text{(anhydrous)}\\ 5.00\ \text{''} & \ldots & \mathrm{H_2O} \end{array} \]
In the solution there should thus have been formed: a mixture of free semicarbazide and its hydrochloride salt in the ratio molecule to molecule:
\[ \mathrm{NH_2.CO.NH.NH_2 + NH_2.CO.NH.NH_2.HCl} \]
Heating for 36 hours at \(100^\circ\mathrm{C}\) gave \(0.44\) g of hydrazodicarbonamide, which amounts to \(85\%\) of the theoretical yield.
The same experiments, carried out at room temperature, even with very long standing, did not give separation of hydrazodicarbonamide.
Thus, the reaction of splitting off hydrazine from two molecules of the semicarbazide salt proceeds in one aqueous solution, but very slowly. It does not proceed at all in alkaline solution (with an excess of alkali).
Potassium acetate, as a salt formed by the cation of a strong base and the anion of a weak acid, is hydrolyzed with formation of active alkali.
\[ (\mathrm{CH_3.COO})'\,|\,\mathrm{K}+\mathrm{H}\,|\mathrm{(OH)}' \rightleftarrows \mathrm{CH_3COOH}+\mathrm{K}\,|\,\mathrm{(OH)}' \]
The active alkali liberates a certain amount of free semicarbazide:
\[ (\mathrm{H_2N.CO.NH.NH_3})\,|\,\mathrm{Cl}'+\mathrm{K}\,|\,\mathrm{(OH)}' = \mathrm{K}\,|\,\mathrm{Cl}'+\mathrm{H_2N.CO.NH.NH_3(OH)} \]
\[ \mathrm{H_2N.CO.NH.NH_3OH \longrightarrow H_2N.CO.NH.NH_2 + H_2O} \]
The latter reacts with semicarbazide hydrochloride, splitting off hydrazine hydrochloride:
\[ \mathrm{H_2N.CO.NH.NH}\boxed{\mathrm{H}} + \boxed{\mathrm{H_2N.CO.}\,|\,\mathrm{NH.NH_3Cl}} = \]
\[ = \mathrm{H_2N.CO.NH.NH.CO.NH_2 + H_2N.NH_3Cl} \]
i.e. for the reaction to proceed forward, the formation of a hydrazine salt is necessary, and, consequently, also the formation of free hydrazine.
In aqueous solution the reaction, although slowly, does proceed, because semicarbazide hydrochloride is hydrolyzed with formation of free semicarbazide:
\[ [\mathrm{H_2N.CO.NH.NH_3}]\,|\,\mathrm{Cl}' + \mathrm{H}\,|\,\mathrm{(OH)}' \rightleftarrows \mathrm{H_2N.CO.NH.NH_3OH + HCl} \]
\[ \mathrm{H_2N.CO.NH.NH_3OH \longrightarrow H_2O + H_2N.CO.NH.NH_2} \]
With an excess of alkali, however, the reaction does not proceed, because free hydrazine would then be formed, whereas the reaction is directed by salt formation.
-
Ber. 30, 1541 (1897). ↩