IKVESTIGATION OF T H E DIFFERENTLY COLORED FORMS OF CERTAIN DERIVATIVES OF DIPHENYLAMINE BY SICHOLAS MICHAEL CULLINANE, OLGA EDWINA EMBREY, AND DANIEL RICHARD DAVIES
A considerable number of substinces are described in the chemical literature as existing in modifications of different color. I n many cases the only differences in properties noted were the colors, in which the variations were usually not very pronounced. Such color differences can frequently be accounted for by the presence of traces of impurity, differences in the degree of fineness of the particles, differences in texture, and pleochroism, the forms being otherwise identical. Thus red phosphorus when fine-grained is scarlet in color, and when coarse-grained is violet. Further, the red and yellow forms of mercuric oxide are identical except in color. Mercuric iodide exists in two dimorphic forms, the red being stable below, and the yellow above, 128’. Yet in liquid air the red form becomes yellow, and in liquid hydrogen, white. The existence of a body in varieties of different color may also be due to polymorphism, and here differences in other physical properties besides color are observed, such as crystalline structure, melting point, solubility, density, these differences being found only in the solid state. On transformation of the solids into the liquid or the vapor state, or by solution, all differences between the forms disappear. Further, the alteration in color of a substance may be caused by change in chemical structure, for instance polymerisation, tautomerism, or stereoisomerism, and in cases of this type differences in properties will persist in the liquid state, or in solution, a t least for some time. Many organic compounds exist in forms of different color, but only in comparatively few cases have the crystallographical structures of physicochemical properties been compared. In the present research a number of compounds were prepared in forms of varying color, and their crystalline structures, densities, solubilities, colors in different solvents and refractive indices of their solutions compared. In some cases the forms were found to be identical in all respects except color, some were shown to be dimorphic, and some were observed to exhibit chemical isomerism. A. Hantzsch’ has prepared several compounds which exist in modifications of different color, termed ‘chromoisomerides,’ and he attributes the change in color to change of structure. Among them are a number of nitroanilines, including some diphenylamines. The forms appear to differ only in the solid state, yielding with the same solvents optically identical solutions, possessing the same colors, refractive indices, and absorption spectra. He states that polymorphism is out of the question since solutions of certain ’chromoisomer’
A. Hantzsch: Ber., 43, I662 (1910).
COLORED FORMS O F CERTAIS DIPHEKTLAMISE DERIVATIVES
143 j
ides’ in different media are different in color, and as the solute is found to be unimolecular it is assumed that the variation in color of the solutions is due to the presence of different ‘chromoisomerides.’ However, it is shown in the present communication that similar variations in color in different solvents exist where there is no indication of chemical isomerism or even polymorphism. Such color differences may be due, a t any rate in some cases, to the presence of solvates, for many such additive compounds, derived from diphenylamines, are known. I n fact Hantzsch,’ in a later paper on acridine derivatives, postulates the formation of solvates to account for similar color variations. Since ‘chromoisomerism’ as observed by Hantzsch appears to be evident only in the solid condition, in order to prove the existence of chemical isomerism he has recourse to a comparison of the physical properties of certain homologous series; for example, the members of the homologous series.
NO2 0
8
0-NR*
where R is methyl, ethyl or propyl, all give yellow solutions in chloroform, and the increments in molecular refraction on replacing methyl by ethyl, or ethyl by propyl, are respectively 9. j and 9.4, these values being in close agreement with the theoretical value 9.2 (Briihl). On the other hand, in the case of the corresponding 3 :4-dinitroanilines, the solutions in pyridine of the dimethyl and diethyl derivatives are respectively yellow and orange, and the observed increment, is 7.8 as compared with the theoretical value 9 . 2 . From this result Hantzsch concludes that the two substances cannot belong to an homologous series, but to two different isomeric series, and hence the difference in color is due to isomerism. I t seems quite likely, however, that this anomalous result is due to the formation in solution of different amounts of the additive compound of solvent and solute, for pyridine is basic and the nitroanilines slightly acidic. Although in some cases the ‘chromoisomeric’ modifications of Hantzsch may be chemical isomerides, yet the existence of isomerism among the nitroanilines does not seem to have been satisfactorily proved by him. His conclusions appear t’o be rather too far-reaching, for polymorphism is in most cases sufficient to account for his experimental results, and it is usual to assume the existence of polymorphism until there is satisfactory evidence of chemical isomerism. I t is also possible that in some instances the forms are actually identical save in color, for although sometimes the melting points differed, in many cases the only distinction observed was in color. I n the present research a number of nitrodiphenylamines of similar constitutions to those prepared by Hantzsch were examined. z :q:6-Trinitro-4‘-methyldiphenylamine(picryl-p-toluidine) exists in two forms, and a crystallographical investigation of them by Lenk2 showed that 1
3
Hantzsch: Ber., 44, 1783 ( 1 9 1 1 ) . J. prakt. Chem., (2) 79, 548 (1909).
1436 NICHOLAS M. CCLLINANE, OLGA E. EMBREY AND DANIEL R. DAVIES
the one modification was composed of yellow or orange-yellow monoclinic needles, and the other of dark red needles belonging to the rhombic system. The results obtained in the present research for the densities of the two forms confirmed this distinction but did not indicate whether the case was one of dimorphism or of chemical isomerism. However, it was further observed, contrary to the statement of Hantzsch' that solutions of picryl-p-toluidine in all media were orange in color, that the colors in solution varied considerably with the solvent, and furthermore that the colors of the two modifications in the same solvent differed considerably in some cases. Thus solutions of equal concentration in acetone were orange-red (yellow form) and orange with a yellow tint (red form); in pyridine very deep orange-red (yellow form) and reddish-orange (red form). I n other media differences in color, though not so pronounced as in these two solvents, were also noticed. The yellow variety always gave the deeper color in solution. Molecular weight determinations in benzene proved here (as in the case of all the compounds examined) that both modifications were unimolecular. The refractive indices of solutions of equal concentration of the two forms in pyridine were different. It was observed that the red form of picryl-p-toluidine yielded with benzene an orange-red solvate of different composition from that furnished by the orange-yellow variety. On heating, both additive compounds were converted into the red solvate-free form, while a t the ordinary temperature both solvates were slowly transformed into the orange-yellow modification of the amine. Further, the latter form was changed into the red variety on heating alone or on standing in contact with acetone. at high temperatures
>-
Red Form
Orange-red Additive Compound
~o0liN1,CsHs.
Additive Compound at
room temperature 2
CnHio0sN1,Cs"I.
From the above results the two modifications of picryl-p-toluidine must be chemical isomerides. I t is interesting to compare the foregoing phenomena with those observed by P. Pfeiffer2 and his coworkers in the case of certain nitro derivatives of stilbene. They found, for example, that 2-nitro-4'-methoxystilbene-4carboxylic acid existed in a yellow and an orange form of identical melting point; these would normally be considered dimorphic modifications except that the following reversible phenomena occurred: the yellow acid gave an Hantasch: Ber., 43, 1679 (1910). ZBer., 48, 1777 (1915);49, 2426 (1916);51, 554 (1918). 1
COLORED FORMS O F CERTAIN DIPHENYLAMINE DERIVATIVES
I43 7
orange pyridine salt, whilst the orange acid gave a yellow pyridine salt of the same composition as the other, the acids being regenerated by treatment with hydrochloric acid. It was found possible to carry out the following reactions:
’
Orange Pyridine Salt HC1
I 1 pyridine
Yellow Acid
pyridine 4
heat
+-
Yellow Pyridine salt HCl
11
pyridine
Orange Acid
The different varieties of the one substance isolated by Pfeiffer yielded identical colors in a given solvent, but the colors varied considerably with the medium employed, this result being attributed by him to the formation in solution of different solvates, some of which were isolated. The melting points of the two modifications of picryl-p-toluidine were observed to be the same, viz., 1 6 j .j o ;this was evidently due to the conversion of one form into the other by heat, since the orange-yellow crystals on being heated gradually turned red at I jo-15 j”. A mixture of the two varieties also gave the same melting point. z :4-Dinitro-~-methyl-2’-methoxydiphenylamine was found by the present authors to occur in two forms of different color. These were then subjected to an optical and crystallographical examination. Owing to the specialised methods of preparation of the forms of this and the other substances herein described it was difficult in some cases to isolate suitable crystals, but in general the results confirmed those obtained by the physico-chemical methods. All the crystallo-optical examinations were carried out by hlr. A. Stuart. In the case of z :4-dinitro-~-methyl-z’-methoxydiphenylamine he reports as follows “These two substances are crystallographically and optically distinct, the one being composed of brownish-yellow transparent monoclinic plates (which become yellow on being powdered) with a maximum extinction angle of 2 7 O , and pronounced pleochroism, and the other of scarlet monoclinic needles with a maximum extinction angle of j”, and pleochroism hardly noticeable. Different crystallographical forms occur in each and no angular measurements correspond.” The densities of the two substances were found to be different, and also the solubilities in chloroform. In contact with acetone the metastable form was transformed into the stable one (this occurred in the case of all the compounds investigated) and hence the solubilities in this solvent were observed to be identical within the limits of experimental error. N o change of either modification took place in presence of chloroform. The stable variety was found to be less soluble than the metastable form. The colors of solutions of z :4-dinitro-5-methyl-z’-methoxydiphenylamine varied with the solvent employed; thus in benzene the color was orange, in acetic acid deeper orange, in alcohol and acetone a little deeper than in acetic acid, in chloroform reddish-orange, and in pyridine reddish-orange (slightly A more detailed and complete report will appear in a future communication.
1438
NICHOLAS
M. CULLINANE, OLGA E. EMBREY AND DANIEL R . DAVIES
deeper than in chloroform). Ths brownish-yellow modification gave a slightly deeper color in the last two media (in all experiments 0.1g. of solute was dissolved in 30 g. of solvent). Also the refractive indices of solutions of equal concentration of the two forms in pyridine were quite different. Hence, the two modifications of 2 :4-dinitr0-5-methyl-z ’-methoxydiphenylamine must be chemical isomerides. The red form turned yellowish on heating, and accordingly the melting points of both varieties were the same. z:4-Dinitro-~:methyl-4’-ethoxydiphenylaminealso crystallised in two forms. Stuart reports: “The two substances are different in respect of color, crystal habit, transparency, and internal structure, one occurring in perfectly translucent bright-yellow monoclinic needles having an extinction angle of 31’; the other in rather opaque orange-red rhomb-like crystals giving no definite extinction between crossed nicols. The nature of these crystals precluded further investigation.” The orange-red solid was produced by the action of heat on the yellow crystals. The latter when rapidly heated shrank considerably at about 125O, turning reddish, and then melted at the same temperature as the other modification. The transition point of the yellow variety is therefore in the neighbourhood of 125’. The densities and solubilities in chloroform of the two forms were different. The bright-yellow modification is the stable one, and it was found to be less soluble than the orange-red solid. Solutions of equal concentration in the one solvent were identical in color, although the colors varied with the medium. The refractive indices of solutions of equal concentration in pyridine were identical within the limits of experimental error. As no differences in properties were observed except in the solid state the two forms of 2:4-dinitro-5methyl-4’-ethoxydiphenylaminemust be considered dimorphic. z :4-Dinitro-z ’-methoxydiphenylamine occurs in two forms of distinctive color, long thin orange-yellow needles and bright red needles. Stuart reports: “The two modifications are very much alike optically despite the startling difference in color. Both show that the length of the needles is the direction of fast vibration; pleochroism in each case is very slight, and extinction straight.” The identity of the two modifications was proved by determinations of their densities and solubilities. The orange-yellow variety on being heated became reddish at about 145’ and melted at 165.5’, which was also the melting point of the red form. In a recent paper by Gallas and Alonsol a red modification of this compound is described, melting a t 165’, and ayellow form which changed to red at 125-145’ and melted at 153-159’. The two forms obtained by the present authors, however, tho prepared by the same methods as those employed by Gallas and Alonso, both melted a t 165.5’. The refractive indices of solutions of equal concentration of the forms were also approximately the same and both were observed to be unimolecular in benzene. Gallaa and Alonso: Anales SOC.Espail. Ffs. Quim., 28, 645 (1930).
COLORED FORMS OF CERTAIS DIPHENYLAMINE DERIVATIVES
I439
I440
NICHOLAS M. CULLINANE, OLGA E. EMBREY AND DANIEL R. DAVIES
I n the case of this substance the physical properties (except the colors) of the two modifications were the same and the colors of solutions of equal strengths in the one solvent were identical, yet the color varied considerably with the medium employed altho there was no indication of isomerism or even polymorphism. z :4 :6-Trinitrodiphenylamine (picryl aniline) was isolated as large reddishorange monoclinic prisms with a mauve colored reflex and also as very small bright-yellow prisms which were similar in appearance, but a complete examination was not possible owing to their minute size. Both varieties melted a t 180.5’. It was noticed that the larger crystals varied from red to orange in color, the exact hue appearing to depend upon their size (in all cases yellowish crystals were forlded on powdering). This possibly accounts for the various descriptions of the amine in the literature, deep red prisms,’ scarlet prisms,2 orange needles,s yellow needle^.^ Bamberger and Mullers considered that there were two forms, orange-red needles and scarlet-red prisms, while Hantzsch6 stated that there was only one, a reddish-orange, modification. The two varieties prepared by us gave the same density, and the solubilities in acetic acid and in chloroform were likewise identical. The colors of the two modifications in the same solvent were alike, but they varied considerably in different media. The forms were both found to be unimolecular in benzene, and the refractive indices of solutions of equal concentration in pyridine were in close agreement. The only difference then noted between the two varieties of picryl aniline was the color; they were identical in all other properties examined. Table I gives a comparison of the colors of solutions of the compounds in various solvents, and also of some other substances (obtained in one form only) of analogous constitutions. The colors were compared by means of a Klett Top Reader Colorimeter (in all cases 0.1g. of solute in 30 g. of solvent was taken). Experimental Part Before carrying out the experiments described below each compound was first of all completely purified by repeated recrystallisation. Then the two forms were prepared and examined. The density determinations were carried out by means of a 2 5 cc. Regnault density bottle, the specific gravities of both solids being determined simultaneously under identical conditions. Water was found to be an unsuitable liquid t o use for in most cases the solids floated (partly at least) on the surface, and also it was not easy to remove air bubbles completely. Light petroleum ether (b.p. 4Oo-5O0), the density of which is considerably lower than that of Ullmann and Nadai: Ber., 41, 1876 (1908). Sudborough and Picton: J. Chem. SOC.,89, 583 (1906). Leemann and Grandmougin: Ber., 41, 130 (1908). * Giua and Cherchi: Gaaz., 49 11, 152 (1919). 5 Ber., 33, 108 (1900). ‘Hantasch: Ber., 43, 1678 (1910).
COLORED FORMS OF CERTAIN DIPHENYLAMINE DERIVATIVES
I441
water, was found to be quite satisfactory. Only a minute trace of either modification dissolved in this liquid, nevert'heless a solution of t'he light petroleum ether saturated at the temperature of the experiment with thesubstance was employed. Any slight differences in solubility between the forms was negligible. Air bubbles were removed by connecting the pyknometer to the pump. The bottle was placed in a vessel of water at the required temperature for a half hour before each weighing was taken. For the determination of the solubilities excess of each solid together with the purified solvent was placed in a flask, fitted with a ground-glass stopper, and immersed in a thermostat at the required temperature, which did not vary by more than 0.1'. The mixture was frequently shaken until equilibrium was attained. A portion of the solution was then transferred to a weighing bottle by means of a pipette (also at the thermostat' temperature). The latter consisted of a glass tube closed at one end and containing near the closed end a small hole corresponding to which was a similar hole in the ground-glass neck of the bott,le. By rotation of the stopper in t'he neck the two holes could be brought into coincidence, and by this means the pressure inside the vessel was made equal to the atmospheric pressure, and then by furt'her rot'ation of the stopper the bottle was made airtight. The weighing-bottle and contents were then weighed and the solvent evaporated off to constant weight. The refractive indices of solutions of each form were determined for sodium light in pyridine by means of a Pulfrich refractometer; and the molecular weights were determined cryoscopically. The solvents used were purified as follows. Benzene W H S obtained pure by removal of thiophene by means of concentrated sulphuric acid, drying over calcium chloride, and distilling. Then it was thrice frozen, dried again, distilled from sodium and fractionated. The acetone after standing over potassium permanganate was distilled, converted into the sodium iodide derivative, and again distilled. After standing over calcium chloride it was once more distilled, treated with potassium carbonat,e and fractionated. The chloroform was successively washed with sodium hydroxide, hydrochloric acid, and water, dried by means of calcium chloride, and distilled from phosphoric oxide. The pyridine was refluxed with quicklime and fractionally distilled. The acetic acid was partially frozen thrice, fractionally distilled, dried, and again fractionated. d:~:6-Trinitro-if,~~eth yldiphenylamine (Picryl-p-Toluidine). The orangeyellow form of t,his compound, according to Busch and Pungs,' was got by addition of hydrogen chloride to a solution of the amine in alcohol containing some alkali, and according to Hantzsch2 by recrystallization from chloroform, carbon tetrachloride, benzene or acetone. It was found by the present authors that by evaporation at the ordinary temperature of a solution of moderate concentration in acetone the orange-yellow cryst'als were usually produced. It was, however, difficult in most cases to prepare the orange-yellow variety uncontaminated by the red. From a solution in alcohol containing a little Busch and Pungs: J. prakt. Chem., 1679 (1910).
* Hantzsch: Ber., 43,
(2) 79,
547 (1909).
I442 NICHOLAS M. CULLINANE, OLGA E. EMBREY AND DANIEL R. DAVIES
hydrochloric acid the orange-yellow solid first separated, but this partly changed on standing to the red form. From benzene an orange-red solvate resulted. The orange-yellow modification was best obtained by recrystallization of the mixed forms or even of the red form from hot carbon tetrachloride. The statement of Busch and Pungs that the red variety can only be converted into the orange-yellow form thro the alkali salt is therefore incorrect. The red form is the stable one and separates from hot concentrated solution in acetone. It is readily obtained pure for the orange-yellow modification on standing in presence of acetone is transformed in a short time into the red compound. According to Busch and Pungs it can also be obtained from benzene containing some alcohol and also from alcohol to which ammonium hydroxide has been added. This form is also said to be deposited from dilute solution in alcohol, and from pyridine. The melting point of the red modification is given by Busch and Pungs as 165'~two degrees higher than that of the orange-yellow form. Hantzsch states that both substances melt a t 164'~while Ullmann and Nadail describe picrylp-toluidine as red needles melting a t 169'. It was observed in the present work that the melting points of both forms were the same, vis. 165.5'~ the orange-yellow crystals on being heated turning red gradually. It was remarked that after heating the orange-yellow variety above its melting point yellow and red crystals separated out side by side on cooling. Prolonged heating of the orange-yellow solid to a temperature just below its melting point caused it to be completely converted into the red. Two additive compounds with benzene were isolated. The orange-yellow crystals were dissolved in boiling benzene and on allowing the solution to cool orange-red needles separated out. These were dried rapidly and a weighed portion heated to 100' for several hours until the weight was constant. Wt. of eample
Benzene found
G.
70
1.5939
1 1 .o
Benzene calcd. for ~CiaHiaOsN4,CsHa 10.9
On heating this solvate it shrank slightly a t about 100-110'and reddened somewhat, becoming quite red at 155-160' and melting at 165.5'. After several weeks a t the ordinary temperature it changed into the orange-yellow form of picryl-p-toluidine, Similar experiments were carried out with the red modification of the amine. The solvate, obtained in the same way as that from the orangeyellow variety, gave the following results on analysis : Wt. of sample G.
Benzene found
%
Benzene calcd. for CisHioOsN4, CaHs
0.6605
20.4
19.7
This solvate also shrank on heating a t about 100' and deepened in color. At about 150' it became quite red and melted at 165.5' to a deepred liquid. Ullmann and Nadai: Ber., 41, 1876 (1908).
COLORED FORMS O F CERTAIN DIPHENYLAMINE DERIVATIVES
1443
The densities of the two forms of picryl-p-toluidine were determined by the method above described and gave the following results: Temp.
Density g./ml.
0
Orange-yellow form Deep-red form
14.2 14.2
1.467 I ,626
The molecular weights of the two forms were determined cryoscopically in benzene, the freezing constant for the solvent, being found by a separate experiment. Mol. wt. found
Orange-yellow form Deep-red form
Mol. wt. calcd. for CisHioOaNi
314; 323 318;315
318 3 18
The refractive indices of solutions of the two forms gave the following results: Solvent
Orange-yellow form
Pyridine
Deep-red form Orange-yellow form Deep-red form
Pyridine Pyridine Pyridine
Stren th of sofn.
% 5
5 2 . 5
2.5
Angle of deflection Mean
Refractive index n?"
Absorption too great; no reading
--
34'38.5' 35'33.5' 35'44.5'
1.51785 I . 51289 I ,51189
d:4-Dinitro-i5-Methyl-Z'-Methoxydiphenylamine. This compound was obtained in two modifications. As a rule slow crystallization a t the ordinary temperature from acetone yielded large brownish-yellow transparent crystals melting at 146' to a deep-red liquid. Slow evaporation of the solvent from a solution in light petroleum ether a t the ordinary temperature, or separation from hot alcohol gave in most cases this form also, which was the stable one, for on allowing the other variety to stand in presence of acetone in the cold it reverted in a short time to the yellow modification. By crystallization from a hot solution in acetone the brownish-yellow crystals were found to be mixed with red needles, which could be obtained in small quantity free from the other form by mechanical separation. On adding cold light petroleum ether to a warm moderately concentrated solution in benzene red mixed with yellow crystals were deposited. The red solid became yellowish on heating; its melting point was also 146' and was undepressed by admixture with the other modification. The preparation of the red variety in quantity uncontaminated by the yellow was difficult. The most satisfactory method consisted in refluxing the amine for 30 mins. with a large volume of light petroleum ether (60-80') containing a little benzene, then decanting rapidly thro a hot filter into an ice-cooled flask. The latter was continuously shaken and the red solid filtered off and dried.
1444
NICHOLAS M. CULLINANE, OLGA E. EMBREY AND DANIEL R . DAVIES
2 :4-Dinitro-s-methyl-2 '-methoxydiphenylamine was found to be readily soluble in benzene, acetone, chloroform, or pyridine, moderately soluble in alcohol, and sparingly soluble in light petroleum ether. Anal. Calcd. for C I ~ H I ~ O:SCN55.4, ~ H 4.7, N,13.9.Found (brownish-yellow form) C 55.1, H 4.5, Tu', 13.9;(red form) C 5 5 . 2 , H 4.4,N 13.9. The following results were obtained for the densities of the two forms:
Temp.
Density g./ml.
0
Red form Brownish-yellow form
1.485 1,414
15.2
15.2
Red form after standing in contact with acetone for three days, the color having changed to yellow: 15.2
I
411
The last result shows that the red modification was converted into the yellow in presence of acetone. Hence, the solubilities of both varieties were found to be the same in this solvent. In chloroform no change in color occurred and the solubilities of the two forms in this medium were quite different. Solvent
Temp
Solubility
G. solute in roo g. s o h . 4.685
0
Brownish-yellow form Red form Brownish-yellow form Red form Brownish-yellow form Red form
24
5
Acetone Acetone Acetone Acetone Chloroform Chloroform
24.5
3 I .93 31.93 3 I .9j 31.95
4.691 5.853 5.853 I 5 ,861 16.998
The molecular weights determined cryoscopically in benzene were as follows: Mol. wt. found
Mol. wt. calcd. for CIIHISOSNS
305 307
303 303
Brownish-yellow form Red form
The refractive indices of solutions of both forms at Solvent
Brownish-yellow form Red form
Pyridine Pyridine
Strength of soln.
% 5 5
2
2
were as follows:
Angle of deflection Mean
34O49/ 3S03l
Refractive index nF'= I I
51691 ,51565
2:4-Dinitro-B-Methyl-4'-Ethoxydiphenylamine. The original product was dark in color, but a more light-colored compound was obtained by dissolving the substance in acetic acid and pouring the solution into much water with vigorous shaking. It was then washed with water and recrystallized several times.
COLORED FORMS OF CERTAIN DIPHENYLAMINE DERIVATIVES
1445
From hot acetone-alcohol by rapid cooling bright-yellow crystals were obtained melting at 148,5'. Similarly rapid recrystallization from warm soht,ions in either of these solvents or precipitation from cold moderately concentrated solution in benzene by means of light petroleum ether yielded the yellow form, which was the stable one. A second modification was formed by heating the yellow solid t o 130' for several hours, the product consisting of orange-red crystals. Both varieties were readily soluble in hot acetone, benzene, acetic acid, pyridine, or chloroform, slightly soluble in alcohol, and sparingly soluble in light petroleum ether. As t,he yellow form was converted into the orange-red on heating without loss in weight the former only was analysed. Anal. Calcd. for C I S N I S O ~:N, N ~ 13.25. Found: N, 13.4. The densities of the two modifications were different, but after standing in presence of acetone the density of the orange-red crystals was observed to be approximately the same as that of the yellow, the specific gravity of which was unaffected by similar treatment. Temp.
Bright-yellow form Orange-red form
0
Density g./ml.
14,2 14.2
1.444 1.371
Orange-red form after standing in presence of acetone for 3 days, the color having changed to yellow: 14.2
1,445
As the orange-red form was transformed into the yellow in acetone the solubilities of both were in close agreement in this solvent. I n chloroform no color change of either form was noted and their solubilities were different in this medium. Temp.
Solvent
0
Bright-yellow form Orange-red form Bright-yellow form Orange-red form Bright-yellow form Orange-red form
31.8 31.8 37.' 37.1 3 I . 9j 31.95
Solubility G. solute in IOO g. s o h .
Acetone Acetone Acetone Acetone Chloroform Chloroform
7.756 7.757 9 ' 789 9 792 19.104 19.343 '
The following results were obtained for the molecular weights, determined cryoscopically in benzene: Bright-yellow form Orange-red form
Mol. wt. found 313 315
Mol. wt. calcd. for CISHI sOSN) 317 317
1446 NICHOLAS
M. CULLINANE, OLGA E. EMBREY AND DANIEL R. DAVIES
The refractive indices of solutions of the two modifications were as follows: Solvent
Bright-yellow form Orange-red form
Pyridine Pyridine
Strength of soln.
%
Angle of deflection Mean
Refractive index n’:
5 5
35O27‘ 35’25’
1.51358 I . 51366
d:4-Dinitro-Z’-Methoxydiphenylarnine. The condensation product was purified by repeated recrystallization from acetone. The two forms were prepared by the following methods, which, however, could not always be repeated : By allowing a hot concentrated solution in alcohol to cool slowly the scarlet variety separated out. On rapid cooling of a warm solution of moderate concentration in acetone orange-yellow flocculent crystals were deposited. This modification was also formed by slow evaporation from a solution in alcohol-acetone. Recrystallization from hot alcohol yielded at a high temperature the red solid; when the solution had cooled to just above the room temperature the orange-yellow crystals were produced. 2 :4-Dinitro-z ‘-methoxydiphenylamine was found t o be soluble in hot acetone, chloroform, pyridine, or glacial acetic acid, moderately soluble in alcohol, and sparingly soluble in light petroleum ether. As the orange-yellow modification became red on heating without loss in weight the former only was analysed. Anal. Calcd. for C13H110~N3 :N, 14.5. Found: N, 14.45. The densities of the forms were as follows: Temp.
Density g./ml.
0
Orange-yellow form
14.4
I
,468
Scarlet form
I4.4
I
,464
The solubilities of both forms were in very close agreement. Temp. 0
Orange-yellow form Scarlet form Orange-yellow form Scarlet form Orange-yellow form Scarlet form
31.5
31.5 37.1 37.1
29.8 29.8
Solvent
Solubility G. solute in 100 g. soh.
Acetone Acetone Acetone Acetone Chloroform Chloroform
4.467 4.461 5.461 5.467 7 . 97 9 7.960
COLORED FORMS OF CERTAIN DIPHENYLAMINE DERIVATIVES
I447
The molecular weights, determined cryoscopically in benzene were as follows : Mol. wt. calcd. for CisHiiOsNa 289
Mol. wt. found
Orange-yellow form Scarlet form
2 7 1 ;282
289
281;zSj
The refractive indices of solutions of the two forms were as follows:
.
Solvent
Strength of soln.
Angle of deflection Mean
Refractive index ":n
j
34'4 j'
1 51727
j
34'44'
1.51736
yo
Orange-yellow form Scarlet form
Pyridine Pyridine
2:4:6-Trinitrodiphenylamine (PicrylAniline). By slow crystallization of the above compound from acetone a t the ordinary temperature reddishorange crystals separated. Crystals of the same color were also obtained from alcohol, even when some hydrochloric acid was present. On pouring a fairly dilute solution of the diphenylamine in boiling acetic acid into a large v o l m e of water with vigorous agitation small bright yellow crystals were precipitated. These were immediately filtered, washed with water, and dried. The densities of the two varieties were as follows: Temp.
Density g./ml.
0
Bright-yellow form Red-orange form
14.1 14.1
1.571
1.570
The following results were obtained for the solubilities of the two forms: Temp. 0
Bright-yellow form Red-orange form Bright-yellow form Red-orange form Bright-yellow form Red-orange form Bright-yellow form Red-orange form Bright-yellow form Red-orange form
24.3 24.3 29.3 29.3 '4.5 14.5 24.3 24.3 29.8 29.8
Solvent
Solubility
G. solute in
Acetone Acetone Acetone Acetone Acetic acid Acetic acid Acetic acid Acetic acid Chloroform Chloroform
100 g.
7.66j 7.658 8.551 8' 567 0.7580
0 , 7jss 0.9065 0.9036 I ,483 I ,489
soh.
I448
NICHOLAS M. CULLINANE, OLGA E. EMBREY AND DANIEL R. DAVIES
The molecular weights determined cryoscopically in benzene were as follows: Bright-yellow form Red-orange form
Mol. wt. found
Mol. wt. calcd. for
306 311
304 304
CnHaOBN,
The refractive indices of solutions of the forms were in close agreement. Solvent
Strength of soln.
70
Angle of deflection Mean
Refractive index
5
34’38’
I
51790
5
34’39‘
I
51781
n200
D
Bright-yellow form Red-orange form
Pyridine Pyridine
In conclusion we wish to express our thanks to Prof. W. J. Jones for his valuable suggestions, and also for his help in the determination of the refractive indices. summary
in two modifications of different color, crystalline structure, and density. Moreover each form yields a different additive compound a i t h benzene, and solutions of equal concentration in pyridine possess different colors and refractive indices. The two forms are therefore chemical isomerides. The two forms of 2 :4-dinitro-~-methyl-z’-methoxydiphenylamine are 2. different in color, crystallographical properties, density, and solubility. Solutions of equal strength in pyridine are different in color and refractive index. Hence, the two modifications are also isomeric forms. 3. The two modifications of 2 :4-dinitro-5-methyl-4’-ethoxydiphenylamine are dissimilar in crystallo-optical properties, density, and solubility. As no distinctions were observed except in the solid state they are considered to be dimorphic forms. 4. The two forms of 2 :4-dinitro-z ’-methoxydiphenylamine and of z :4 :6-trinitrodiphenylamine are of distinctive color. The modifications appear to be similar in crystallographical properties, and their densities, solubilities, colors and refractive indices of solutions of equal concentration are in very close agreement. The two forms are therefore identical save in color. I.
z :4 :6-Trinitro-4’-methyldiphenylamine exists
Universatv College, Cardiff, Wales. February 6, 1952.
