[CONTRIBUTION FROX THE CHEMICAL L.4BORATORY OF THE U N I V E R S I T Y OF ILLINOIS]
SALTS OF NITRO COMPOUNDS. 11. T H E REACTION O F T H E SILVER SALT OF PHENYLNITROMETHANE WITH DIPHENYLBROMOMETHANE G. B. BROWX
AND
R. L. SHRINER
Received October 8, i9SY
A previous study of the alkylation of the silver salt of phenylnitroacetonitrile (I) with methyl iodide or benzyl chloride showed that unstable nitronic esters were produced' indicating that oxygen-alkylation had occurred. However, Wieland and Hochtlen2 obtained a-nitro-a P ,P-triphenylpropionitrile (11) by treatment of this same silver salt (I) with diphenylbromomethane. This reaction CN
CN
I + (CaH6)2CHBr+ CBH5--C-N02
CsH6CNo2Ag
I
f AgBr
AH (C6H6)2 I1
involved carbon-alkylation, and indicated that diphenylbromomethane behaved differently from methyl iodide or benzyl chloride. Since this seemed rather unusual, a study was made of the reaction between the silver salt of a primary nitro compound, phenylnitromethane (111), with diphenylbromomethane in order to determine whether carbon-alkylation would produce the compound IV by the following reaction: C6H6C"02Ag I11
4- (C6H6)&HBr + CsHjCHNOz f AgBr ~
CH (CsHs)2 IV
A careful examination of the products of this reaction has shown that no compound corresponding to formula IV was produced. Instead, two compounds were isolated: sym-tetraphenylethane (V) and 1,2-dinitro-l, 2diphenylethane (VI). 1
THURSTON AND SHRINER, J. ORG. CHEM.2, 183 (1937). WIELANDAND HOCHTLEN, Ann., 606, 237 (1933). 376
377
SALTS O F NITRO COMPOUNDS
+ 2 (CsH5)zCHBr + (CBH~) 2CHCH (CGHJ +
2C6H5CHN02Ag
2
v
NO2 NO2
I
1
+ 2AgBr
C6H5-CH-CH--C~H5
vr
These products were evidently formed by two simultaneous coupling reactions. The silver salt is very unstable and decomposes on standing or shaking in benzene solution, depositing metallic silver. NO2 NO2 2CsH5CHN02Ag
-+
1
1
C~H~CH-CH-C~HS VI
+ 2Ag
The free silver then caused coupling of two molecules of diphenylbromomethane to produce sym-tetraphenylethane (17). 2(C6H5)2CHBr
+ 2Ag -+ (C6H5)2CH-CH(C6H5)2 + 2AgBr 17
The sym-tetraphenyletbane (V) was readily characterized by comparison of the melting point with that of a mixtue with an authentic specimen. The 1!2-dinitro-l ! 2-diphenylethane (VI) decomposed over a considerable range (224'-240') when attempts were made to determine its melting point in a capillary tube. It melted with decomposition a t 231-233' on the Maquenne block. This molecule also contains two similar asymmetric carbon atoms and hence may exist in meso and racemic modifications. Both of these forms had been prepared previously by Schmidt3 and by Wieland4 by treating stilbene with nitrogen dioxide. NO2 NO2 C,jH&H = CHCcH5
+ 2NO2
I
+
/
C~HSCH-CHC~H~
This preparation was repeated and the two forms isolated. One form (a-isomer) melted with decomposition a t 230-233' and the other form (p-isomer) melted at 154-155'. The /3-form could be converted to the a-form by heating a sample just above the melting point for a minute and allowing it to resolidify. No data are available to indicate which of these forms is meso and which is racemic. SCHMIDT, Ber., 34,623,3537 (1901). ~WIELAND Ann., , 424, 105 (1921).
378
G. B. BROWN AND R. L. SHRINER
The p-form was also obtained by treating the sodium salt of phenylnitromethane with iodine. NO2 NO2 2C6H5CHN02Ka+ I2
I
---f
1
+ 2NaI.
CeH,CH-CHCsH6
The compound from this reaction was shown to be identical with the Pform obtained by the nitrogen dioxide reaction with stilbene. Mixtures of the a-form obtained synthetically with that produced by the action of diphenylbromomethane on the silver salt of phenylnitromethane decomposed at 230-233" on the Maquenne block thus indicating that they are identical. The 1,2-dinitro-l, 2-diphenylethane was further characterized by conversion to triphenylisoxazole (VII) by treatment with alkali.5 The compound from the coupling reaction (a-form) and the synthetic a- and NO2 NO2
I
/
CGHr,CH--CHCsHr,
NaOH
CoHj-C=N
\ /"
1
CsHj-&c
I
CeHs p-forms yielded the same triphenylisoxazole, melting at 214-215'. These results indicate that the second product of the action of diphenylbromomethane on the silver salt of phenylnitromethane is 1'a-dinitrolf2-diphenylethane. EXPERIMENTAL
Pheny1nitromethane.-This compound was obtained as a yellow liquid boiling a t 114-115" a t 13 mm. according to the procedure described by Wislicenus and Enders.6 S o d i u m salt of pheny1nitromethane.-Sodium (0.9 g.) was dissolved in a mixture of 10 cc. of absolute alcohol and 10 cc. of ether. One hundred cubic centimeters of ether was added, followed by 5 g. of phenylnitromethane in 25 cc. of ether, with stirring. The white, flocculent sodium salt precipitated, was collected on a filter, washed with absolute ether, and preserved in a vacuum desiccator. The yield was almost quantitative. Anal. Calc'd for C,HBNbiaOZ:Na, 14.46. Found: S a , 14.46, 14.40. Silver salt of pheny1nitrornethane.-A solution o f 5.35 g. of silver nitrate in 150 cc. of water was added to 5 g. of sodiumaci-phenylnitromethane in 150 cc. of water, with 5 NENITZESCU, Ber., 62B,2669 (1929); HEIM,i b i d . , 44,2016 (1911); MEISENHEIMER, ibid., 64,3206 (1921). The mechanism of this reaction has not yet been established. 6 WISLICENUS AND ENDERS,ibid., 36, 1755 (1902).
SALTS OF NITRO COMPOUNDS
379
vigorous stirring. The silver aci-phenylnitromethane separated immediately as a white precipitate. It was filtered, washed with ether, and then with petroleum ether. The salt is very unstable and turns brownish-black quickly. The yield was 7.2 g., or 94 per cent of the theoretical. The salt explodes when heated. Reaction between silver aci-phenylnitromethane and dipheny1bromomethane.-To a suspension of 7 g. of the silver aci-phenylnitromethane in 200 cc. of dry benzene was added a solution of 7.5 g. of diphenylbromomethane' dissolved in 50 cc. of benzene, with stirring and cooling. This reaction mixture in various runs was stirred from 7.5hours to four days. One run was allowed to stand for five weeks without stirring. The solution soon turned dark, and in the longer runs a silver mirror formed on the flask. The benzene solution was separated from the insoluble silver salt by filtration, and dried over magnesium sulfate; the benzene removed by distillation, and the residual oil was taken up in 250 cc. of warm absolute alcohol and allowed to crystallize. The first crop of crystals consisted chiefly iif tetraphenylethane, which was purified by three recrystallizations from absolute alcohol. It melted a t 210°, and the melting point of a mixture with a pure sample of tetraphenylethane showed no depression. Considerably larger amounts of tetraphenylethane were obtained in the experiments in which the reaction mixture was stirred a longer time. Concentration of the alcohol filtrate yielded a mixture which was separated by three to five recrystallizations from xylene rind a final recrystallization from alcohol. obtained melted with decomposition a t 231-233", The 1,2-dinitro-lj2-diphenylethane as determined by means of the Maquenne block. The melting point of a mixture prepared from stilbene with a sample of the a-form of 1,2-dinitro-l,2-diphenylethane, and nitrogen dioxide, was 230-234", as determined by means of the Maquenne block. Melting points taken by the capillary tube inethod vary from 224-240", depending on the rate of heating and the size of the c5pillary tube. Previous investigators3*4 report melting points varying from 230-235" to 234-236". Anal. Calc'd for Cl4Hl2N2O4: C, 61.75;IT, 4.42;N, 10.3. Found: C 61.77,61.83;H, 4.62,4.45;N,9.57,9.49,9.82,9.98. The nitrogen analyses carried out by the l h m a s method were always low. A small sample of the 1,Z-dinitro-1,Z-diphenylethaie was decomposed by heating slowly t o 235"in a small test tube. The evolution of nitrogen dioxide was evident, and carbonization took place rapidly. The low analyses were evidently due to this faculty of evolving the oxides of nitrogen on heating, the unreduced oxides being caught by the potassium hydroxide. Attempts to determine the nitrogen by the Kjeldahl method, zinc or sodium tk$osulfate being used as the reducing agent, were also unsuccessful. 1 ,d-Dinitro-i ,d-diphenylethane. A . From stilbene.-The procedure described by Schmidt was followed. Nitrogen dioxide, generated by heating lead nitrate, was passed into a benzene solution of stilbene. Crystallization took place gradually. The crystals were filtered, washed with benzene and recrystallized from alcohol. The decomposition point, as determined by means of the Maquenne block, was 230233". The filtrate and the wash benzene were shaken with 1 per cent sodium bicarbonate solution, and the benzene was removed by evaporation, leaving a yellow powder. On crystallization from ether, followed by recrystallization from acetic acid, broad, flat, needle clusters, melting point 154-155",were obtained. This p-, or low-melting form, was converted to the a-, or high-melting form, by heating above its melting point for a few minutes and allowing to resolidify. 7
COURTOT, Ann. chim., [9],6,80 (1916),
380
G . B. BROWN AND R . L. SHRIKER
B . From sodium aci-phenylnitromethane and iodine.-A solution of iodine in potassium iodide was slowly added t o 2 g. of sodium aci-phenylnitromethane in 10 cc. of water until a slight excess was present. The solution was stirred for three hours, and a few cubic centimeters of dilute sodium thiosulfate was added t o remove the last traces of iodine. 'The solution was extracted twice with 25 cc. of benzene, the extract was dried over calcium chloride, the benzene was distilled and the oily product was crystallized twice from alcohol, yielding the p-form of 1,2-dinitro-l,2diphenylethane; melting point, 151-153". The melting point of a mixture with a sample of the @form, prepared by the reaction of nitrogen dioxide with stilbene, was 151-153'. Triphenylisozazo1e.-Approximately 50 mg. of the 1,%-dinitro-l,2-diphenylethane, prepared in the reaction of nitrogen dioxide and stilbene, was treated with 5 cc. of 30 per cent sodium hydroxide solution and heated on the steam bath for three hours. The crystals of triphenylisoxazole were filtered and recrystallized twice from acetic acid. It melted a t 214-215' which checked the values in the literature.5 Anal. Calc'd for C~IHIINO: C, 84.83; H, 5.05; N, 4.72. Found: C, 84.28; H, 5.54; N, 4.60, 4.85. Triphenylisoxazole was also prepared, according to the above procedure, from approximately 30 mg. of the 1,2-dinitr0-1,2-diphenylethaneprepared by the reaction of silver aci-phenylnitromethane and diphenylbromomethane. It also melted a t 214-215", and the melting point of a mixture showed no depression. Decomposition of the silver salt of phenylnitr0methane.-Five grams of the silver salt of phenylnitromethane was placed in 150 cc. of benzene and shaken for 17 days. The unchanged silver salt was removed by filtration and the colloidal silver was removed by passage through a layer of Xorite on a sintered glass funnel. The solution was dried over calcium chloride, and the benzene was removed under reduced pressure. Two recrystallizations of the residue from ethyl alcohol yielded the &form of I ,2-dinitro-l,2-diphenylethane me1 ting a t 153-154". The alcoholic filtrate from the recrystallizations was mixed with 10 cc. of 30 per cent. sodium hydroxide solution and heated on the steam bath for three hours. When this mixture cooled crystalti of triphenylisoxezole melting a t 213-214" xere obtained. SUMMARY
The reaction of the silver salt of phenylnitromethane and diphenylbromomethane resulted in a coupling of the nitro compound to give 1,2dinitro-l,2-diphenylethane and of the diphenylbromomethane to yield sym-tetraphenylethane.
