[CONTRIBUTION FROM THE
DEPARTMENT OF CHEMISTRY
OF THE UNIVERSITY
OF TEXAS]
THE REDUCTION OF NITROPARAFFINS IN LIQUID AMMONIA GEORGE W. WATT
AND
CECIL M. KNOWLES1.2
Received August 7, 19&
As a part of an extensive investigation of the reduction of organic nitro compounds in liquid ammonia (l), we have studied the behavior of nitroethane, 1-nitropropane, 2-nitropropane, 1-nitrobutane, and 2-nitrobutane toward (a) liquid ammonia, (b) hydrogen generated by the addition of sodium to liquid ammonia solutions of ammonium bromide, and (e) liquid ammonia solutions of sodium. It has been found that these nitroparaffins dissolve in and react with anhydrous liquid ammonia a t -33.5’ to form relatively unstable ammonium salts of the type R-CH=N(+O)O-NH4+. All of these salts are white crystalline solids which decompose slowly with liberation of ammonia. Qualitatively, the decreasing order of stability of the corresponding ammonium salts was found to be : 2-nitropropane > 2-nitrobutane > 1-nitropropane > 1-nitrobutane > nitroethane. The formation of metal salts by the aci forms of the nitroparaffins is well known (2,3, 4) and the existence of ammonium salts has been suggested (5). In 1905,Franklin and Kraus ( 6 )reported the isolation of compounds which they represented by the formulas CH3N02.NH3,CHaNO2.2NH3,CH(N0.J3 .NH3, and C(NO&.NHa. The composition of the first of these compounds was established by deammonation of the second, that of the second and third was determined from the weight of ammonia retained when a known weight of nitro compound was exposed to liquid ammonia, while the ammonia content of “trinitromethane ammonia” ( 6 ) was determined volumetrically. When sodium is added to liquid ammonia solutions containing a nitroparaffin together with an excess of ammonium bromide, the quantity of hydrogen liberated is found to be almost exactly equivalent to the quantity of sodium added. Removal of the solvent and decomposition of the ammonium salts results in recovery of the nitroparaffins. Addition of sodium to solutions of these nitroparaffins in liquid ammonia results in liberation of hydrogen, the formation of white precipitates (probably the sodium salts), and after addition of ammonium bromide, the isolation of the corresponding alkylhydroxylamines, solutions of which readily reduce ammoniacal silver nitrate at room temperature.
O-N&
/ RCH=N I 0
+ Na -+
RCH=N
/o-Na+ I
+ “,+ 1/2Hz
0
1 Research Assistant (1942-43), The University of Texas Research Institute, Project No. 25. 2 Present address: General Aniline and Film Corporation, Grasselli, New Jersey. 540
REDUCTION OF NITROPARAFFINS
RCH=bT
/o-Na+ + 4Na + NHa L
541
+
0
1
[RCH-N-O-]3Na+
-
I
I
[RCH-N-O-]3Na+
I
+ 3NH4Br
RCHzNHOH
+ NaOH + NaNHz
+ 3NaBr + 3NHs
The yield!s of hydroxylamines are low due to slow and incomplete reduction and to difficulties encountered in the separation of small quantities of these products from relatively large quantities of inorganic salts. No success attended efforts to isolate reduction products other than the substituted hydroxylamines. The reaction ratios reported below provide an indication of the extent of reduction in each case. In connection with the isolation of alkylhydroxylamines as their condensation products with p-nitrobenzaldehyde, it was found that these derivatives must be prepared under anhydrous conditions. In the presence of water, they are hydrolyzed to the oxime of p-nitrobenzaldehyde and the corresponding alcohols. The reduction of nitroparaffins to the corresponding hydroxylamines has been accomplished previously by means of a rather wide variety of reducing agents. Since these reactions have been reviewed recently by Hass and Riley (7), it seems unnecessary to give further details here. On a comparative basis, however, it is significant that reduction by sodium in liquid ammonia at its boiling temperature provides the same degree of reduction as is realized through the use of other reducing rsystems at much higher temperatures. EXPERIMENTAL
Materiar's. The nitropropanes and nitrobutanes were generously supplied by The Commercial Solvents Corporation. Nitroethane was obtained from the Eastman Kodak Company. All other materials were prepared as described by Knowles and Watt (8). Methods. All reactions in liquid ammonia were conducted as described previously (8). Formation of ammonium salts. A sample of each pure nitroparaffin was added t o a large excess of pure anhydrous liquid ammonia a t -33.5", in which all of the ammonium salts were soluble. After complete removal of the solvent, the white crystalline ammonium salts were subjected to such analyses as were possible in view of the instability of the products. I n each case, spontaneous or induced decomposition resulted in liberation of ammonia a,nd regeneration of the nitroparaffin. The ammonium salts of nitroethane and 1-nitrobutane were BO unstable t h a t reproducible analytical data could not be obtained. Data relatiive t o the other salts are given below. 1-Nitropropane: A n a l . Calc'd for CsHsN02-NH4+: "I+, 16.97. Found: NHd+, 16.70. 2-Nitropropane: A n a l . Calc'd for CsHeNO2-NH,+: NHd+, 16.97; N , 26.40. Found: NH4+,16.86; N , 26.61. 2-Nitrobutane: A n a l . Calc'd for C*H&TOZ-NHS: "I+, 14.98. Found: NH4+, 14.78. Reduction by hydrogen. Failure of any of these compounds to react with hydrogen is illustrated by the following example. Upon addition of 4.90 g. (0.2133 gram-atom) of sodium t o a liquid ammonia solution containing 3.00 g. (0.0337 gram-mole) of 2-nitropropane
542
GEORGE
W. WATT -4ND
C E C I L M.
KNOWLES
together with an excess of ammonium bromide, 0.2128 gram-atom of hydrogen was collected. After evaporation of the solvent and decomposition of the ammonium salt, the 2-nitropropane was recovered. Reduction by sodium. Nitroethane. Small pieces of sodium (2.29 g. or 0.0995 gram-atom) were added slowly to a liquid ammonia solution of 3.06 g. (0.0408 gram-mole) of nitroethane. Hydrogen was evolved during the addition of sodium and a white solid separated from the solution. After the first appearance of the blue color characteristic of a liquid ammonia solution of sodium, a slight excess of sodium was added and the reaction mixture was stirred for one-half hour, during which there was no further visible evidence of reaction. The excess sodium was then destroyed by addition of an excess of ammonium bromide. From these data and the fact that a total of 0.0225 gram-atom of hydrogen was collected, the reaction ratio (8) was found to be 1.88. After removal of the solvent, the organic reaction product was extracted into anhydrous ether, treated with dry hydrogen chloride, and the resulting viscous insoluble product was separated, dissolved in absolute ethanol and treated with a solution of p-nitrobenzaldehyde in absolute ethanol in the presence of solid sodium hydrogen carbonate. After twelve hours, the reaction mixture was filtered, the filtrate was evaporated t o dryness, and the residue was recrystallized from ethyl ether t o provide pale yellow crystals of the condensation product (9) of ethylhydroxylamine and p-nitrobenzaldehyde, m.p. 122-123" cor. A n d . Calc'd for COHION~OS: N, 14.43. Found: N, 14.35. The ethylhydroxylamine hydrochloride from another reaction (in which the reaction ratio was 1.90) was dissolved in 95% ethanol and treated with an aqueous ethanolic solution containing p-nitrobenzaldehyde and sodium hydrogen carbonate. After twelve hours, dilution with water and cooling provided a white crystalline solid which was recrystallized from aqueous ethanol. The resulting product melted a t 128-129" cor. and no depression in melting temperature was observed when this material was mixed with an authentic specimen of the oxime of p-nitrobenzaldehyde, m.p. 128-129" cor. Anal. Calc'd for CZHGN~O~: X , 16.86. Found: N , 16.75. A small sample of the condensation product of ethylhydroxylamine and p-nitrobenzaldehyde was prepared under anhydrous conditions and thereafter suspended in hot water for one hour. Sfter filtration and cooling, the oxime of p-nitrobenzaldehyde crystallized and the solution gave a positive test for alcohol (formation of iodoform). I n this and in each of the cases described below, solutions of the substituted hydroxylamines (liberated from their hydrochlorides) readily reduced ammoniacal silver nitrate a t room temperature. 1 -Nitropropane. I n the manner described above, 3.97 g. (0.0446 gram-mole) of l-nitropropane was reduced by 2 80 g. (0.1217 gram-atom) of sodium. Hydrogen was evolved during the reduction reaction and a total of 0.0448 gram-atom of hydrogen was collected. Hence, the reaction ratio was 1.72. The product, n-propylhydroxylamine, was separated as described above and converted to the p-nitrobenzaldehyde condensation product, m.p. 77-78' cor. Anal. Calc'd for C10H12Y203: N, 13.45. Found: N, 13.55. 2-Nitropropane. I n a similar manner, 4.73 g. (0.0532 gram-mole) of 2-nitropropane was reduced by 4.69 g. (0.2040 gram-atom) of sodium. Hydrogen was not evolved during the primary reduction reaction but 0.0743 gram-atom of hydrogen was collected when unreacted sodium Tvas destroyed by addition of ammonium bromide. The reaction ratio was 2.44. The isopropylhydrosylamine was extracted into absolute ether, from which i t was isolated as the hydrochloride (10). dnnE. Calc'd for C3H9N0.HC1:HC1, 32.71. Found: HC1, 32.75. I-Nitrobutnne. Hydrogen was evolved and a white precipitate appeared during the reduction of 3.60 g. (0.0349 gram-mole) of I-nitrobutane by means of 6.94 g. (0.3018 gramatom) of sodium. Since 0.1770 gram-atom of hydrogen was collected, the reaction ratio was 3.56. By the methods already described, the substituted hydroxylamine was separated and converted to the hydrochloride (an oil) which was then dissolved in ethanol and treated
REDUCTION OF NITROPARAFFINS
543
with chloropl?tinic acid. The resulting yellow chloroplatinate was recrystallized from aqueous methanol. Anal. Calc'd for (C~HIINO)~.HzPtCls: N , 4.76; Pt, 33.20. Found: N , 4.77; Pt, 33.35. S-Nitrobutane. Reduction of 3.87 g. (0.0375 gram-mole) of 2-nitrobutane by 3.38 g. (0.1470 gram-atom) of sodium occurred without liberation of hydrogen. However, 0.0201 gram-atom of hydrogen was collected when unreacted sodium was destroyed by addition of excess ammonium bromide. Hence, the reaction ratio was 3.48. The substituted hydroxylamine was separated and converted to its condensation product with p-nitrobenzaldehyde i n the manner described for nitroethane. After recrystallization from petroleum ether, this product melted a t 80-81" cor. -4nal. Calc'd for CllH14N20a: N, 12.61. Found: N , 12.50. Hydrolysis of this condensation product gave the oxime of p-nitrobenzaldehyde and a positive ilodoform test. SUMMARY
1. Five nitroparaffins have been shown to react with anhydrous liquid ammonia at, - 33.5' to form white crystalline and rather unstable ammonium salts The decreasing order of stability of of the type, R-CH=N(+O)O-NH,+. these salts is: 2-nitropropane > 2-nitrobutane > 1-nitropropane > 1-nitrobutane > nitroethane. 2. These nitroparaffins are not reduced by hydrogen generated by the addition of sodium to liquid ammonia solutions (at - 33.5') containing ammonium bromide. 3. Reduction of these nitroparaffins by liquid ammonia solutions of sodium a t -33.5' has been found to be slow and incomplete and to yield the corresponding alkylhydroxylamines. 3. The condensation products of alkylhydroxylamines and p-nitrobenxaldehyde have been shown to undergo hydrolysis to the oxime of p-nitrobensaldehyde and the corresponding alcohols. AUSTIN,TEXAS. REFERENCES (1) KNOWLES AND WATT, J . A m . Chem. Soc., 66, 410 (1943). (2) MEYER,A n n . , 171, 1 (1874). (3) HANTZSCH, Ber., 32, 575 (1899). ( 4 ) THURSTON AND SHRINER, J. Org. Chem., 2, 183 (1937). (51 FRANKLIN A N D KRAUS, A m . Chem. J., 23, 302 (1900). (6) FR.4NKLIN AND KRAUS,J . A m . Chem. S O C . , 27, 210 (1905). (7'1 HASSA N D RILEY,Chem. Rev.,32, 390 (1943). (8) KNOWLES AND WATT,J . Org. Chem., 7.56 (1942). (9) PIERRON, Bull. SOC. chim., [3] 21, 780 (1898). (10) K J E L L I N , Ber., 30, 1891 (1897).
