Identification of Organic Bases by Means of the Optical Properties of Diliturates (Nitrobarbiturates) Aliphatic Amines ELMER M. PLEIN AND BARTLETT T . DEWEY University of Washington, Seattle, Wash., and University of Colorado, Boulder, Colo.
D
ILITURIC acid (5-nitrobarbituric acid) has been suggested as a satisfactory reagent for the separation of potassium and sodium (7, 9) and for the isolation and determination of many organic and inorganic bases (15). Fredholm (9) determined the ratios of solubilities of alkali and alkaline earth diliturates and presented photomicrographs of several of them. Chamot and Mason (6) also gave photomicrographs of diliturates of inorganic bases and reported the use of the acid in identifying the bases by the appearance of the crystals developed. Larsen (IS) determined the optical properties of diliturates of amino acids as a means of their identification. Dilituric acid can be prepared by the direct nitration of barbituric acid (1, 9-19, 17) and by other methods (1-4, 16). The acid is easily purified (9,11). This investigation was undertaken to determine whether it was possible to use the optical constants of diliturates to identify the organic bases. Melting-point determinations of the diliturates are of no value because the compounds decompose upon heating.
Preparation of the Diliturates Equivalent quantities of dilituric acid (from Eastman Ilodak Company) and the amine were dissolved in a minimum of boiling water and the solution was allowed t o cool ( 1 5 ) . The salts possess high-temperature coefficients of solubility which alloLy purification by recrystallization. F i c h diliturate was recrystallized one or more times.
Analysis of the Diliturates Dilituric acid and the diliturates were dried t o constant weight in a vacuum oven a t 80” and analyzed for nitrogen by the Kjeldah1 method modified to include nitro compounds. The deviation of the percentages found from those calculated did not exceed 0.20 except for the following salts: 2-aminobutane, calculated 22.76, found 22.52; propylenediamine, calculated 26.98, found 26.67 ; a-methylhydroxylamine, c a l c u l a t e d 25.45, found 25.78; hydroxylamine, calculated 27.18, found 26.84; 2,4-diaminobutane, calculated 25.80, found 25.40. The results for these five were obtained with the addition of glucose as a reducing agent (8). The salts of ethanolamine and hydrazine were analyzed by the semimicro-Dumas method (14). The results for ethanolamine checked closely n.ith the theoretical; hydrazine diliturate, :alculited 34.14, found 34.50.
Determination of Optical Properties The optical crystallographic data presented in Table I were determined by methods described b y C h a m o t a n d
Mason (5) and by Winchell (18). The highest index of refraction in the authors’ set of liquids was 1.785; hence no value above this figure is reported. The highest index of refraction for isobutylamine diliturate could not be determined because of the difficulty experienced in orienting the crystals properly. Hydroxylamine diliturate possesses very weak dispersion; hence this property was not obtained. Ammonium diliturate does not show a true value for any principal index in the usual orientations, but the values can be determined from crushed crystals. The diliturates of n-butylamine, ethanolamine, ethylamine, ethylenediamine, methylamine, a-methylhydroxylamine, and isopropylamine show but one index, p, in the usual orientation. All the other compounds present two true indices in the most frequent orientations. All extinction angles were measured in the acute angle, 6. I n Table I1 are recorded some optical and crystallographic values which were observed on the most frequently occurring orientations of the crystals. Most of the diliturates of the primary aliphatic amines are so flattened that the crystals tend to assume a common orientation when suspended in an immersion liquid. The optical orientation designated as acute, obtuse, or optic normal indicates that a centered interference figure is found in the usual position of the crystals. The descriptive term “inclined” indicates that the interference figure is not centered. In these inclined obtuse orientations one of the optic axes usually presents itself, but the view of the crystal is essentially on the obtuse bisectrix side. Thick crystals of ammonium diliturate present no definite orientation, hence “variable” optical orientation for
TABLE T. OPiwaL PROPERTIES OF SOMEDILITURATES OF PRIMARY AMINES A N D OF DILITURIC ACID Diliturate
Extinrtion Angle
Dilituric acid 31 2-Aminobutane Parallpl 2-Amino-n-ortane 30 Ammonium 44 Isoamylamine 6 n-Amylamine Parallel Bensylamine Parallel Isobutylamine 41 n-Butylamine 43 Cyclohexylamine 29 2.4-Diaminobutane 39 Dieth ylenetriamine 26 Ethanolamine 39 r.thylamine 43 Ethylenediamine 44 n-Heptylamine Parallel Hydrazine 26 Hydroxylamine 25 Irethylamine 31 ar-~fethylhydroxylaniinp 39 Isopropylamine 43 n-Propylamine Para!lel Propylenediamine 28
534
Optic Sign
-
-
-
A
-
f -
Refractive Indices Alpha Beta Gamma
1 388 1.452 1.460 1.427 1.4.56
1.684 1.650 1.635 1.772 1.644 1.614 1.766 1 TO6
> 1.785 >
1.662 1.647 1.785 1.672 1 679 1.785
1,596 1.418 > 1.470 1.476 1 704 i : k 1.483 1 648 1.697 1.433 1761 > 1.785 1.446 1.731 1.736 1.438 1744 1.777 1.459 1.734 >1.785 1.454 >1.785 > 1.785 1.392 1.616 1 660 1.458 1.748 1.783 1 487 1.748 1.763 1.426 1.696 > 1.785 1.416 1.702 >1.785 1.447 I 701 1.782 1,606 1.619 1.701 1.452 > 1.785 > 1.783
Elongation
-
+
*
* * + -
2-
* * *
-
Dispersion V > P P > V
P>v v
v v
>p >p >p
V > P
lione
r >P V > 3
v>P V > P
>
\’ p V > P V > P v P Y p
> >
V’YP
Y
>
7 ‘
>p
p V > P
v
>p
August 15, 1943 TABLE 11.
535
ANALYTICAL EDITION APP.4RENT PROPERTIES O F PRIMARY ALIPHATIC AMIN?, DILITURATES FROM
MOSTFREQUENTLY OBSERVEDORIENTATION
Diliturate
System
Optical Orientation
Habit
Dilituric acid 2-A4minobutane
Monoclinic Orthorhombic
Tabular Acicular
2-Amino-n-octane Ammonium
Monoclinic Monoclinic
Isoamylamine n-Amylamine
Monoclinic Orthorhombic
Acicular Foliated
Benzylamine
Orthorhombic
Tabular
Iaobutylamine n-Butylamine
Monoclinic Monoclinic
Foliated Tabular
Cyclohexylamine 2,4-Diaminobutane
Monoclinic Monoclinic
I z;lia;ia; Tabular
{
$5;
Diethylenetriamine
Slonoclinic
Lamellar
Ethanolamine
Slonoclinic
Lath-shaped
Ethylamine
Monoclinic
Lath-shaped
Ethylenediamine
llonoclinic
Tabular
n-Heptylamine
Orthorhombic
L a m e11a r
Hydrazine Hydroxylamine
Monoclinic llonoclinic
Columnar Tabuiar
hlethylamine
llonoclinic
L a m e11a r
u-Xlethylhydroxylamine
Monoclinic
Tabular Lamellar
Isopropylamine
Monoclinic
Tabular
n-Prop ylamine
Orthorhombic
Lamellar
Propylenediamine
;\lonoclinic
Lamellar
1.388
Obtuse Optic normal Obtuse Variable Inclined obtuse Acute Optic normal Optic normal Obtuse Inclined obtuse Obtuse Optic normal Optic normal Inclined obtuse Inclined obtuse Inclined obtuse Opt10 normal Obtuse Optic normal Inclined obtuse Inclined obtuse Optic axis Inciined obtuse Optic normal Obtuse
Extinction Angle Parallel Parallel
Refractive Indices 1,388 1.452
1.684 1,662
6 Variable 0-15
1.469 Variable i'ariable
1:635 Variable > 1.785
6 Parallel
1.644 1,596
Parallel
1.448
14 Parallel
1.470 Variable
Parallel 20 20-30 Parallel
1.483 1,455
1.446
1.731
39
Variable
1,744
Parallel
S'ariable
1.734
44
Variable
> 1,785
1,672 1.679 >1.785 1.706 1.704 1.648
> 1.785
Parallel
1.592
1.660
24 25
1.468 1.487
1,748 1.763
Parallel
Variable
1.696
38
Variable
...
1.702 1.702 1.701
43
Variable
Parallel
1.606
1.701
21
1.452
> 1.782
-7
1
those which possess equant habit. Tabular c r y s t a l s of t h e a m monium compound show an inclined o b t u s e b i s e c t r i x figure. Apparent refractive indices of some of the compounds could not be satisfactorily determined within narrow limits and are therefore reported as variable. These variable indices of all compounds besides equant ammonium are greater than the true index a, but less than the true index 0. Crystal habit is described according to Winchell (18). In Figures 1 and 2 a r e d i a g r a m s of t h e crystals as they appear in the most frequently occurring orientations. Observed refractive indices (in the direction of the dotted lines) and observed crystal angles are recorded on most of
1 662
- + -1.452
DILITURIC ACID
2-
AMINOBUTANE 2- AMINO-n- 0CTANE
1.644
ISOAMYLAMINE
1.679
n- AMYLAMINE
goo
BENZYLAMINE 1.455
1210
n- B U T n A M I N E
A
[ 1,455
ISOBUTYLAMINE 1 731
m o d -
90"
CYCLOHFXYLAMINE
2,4-DIAMINOBUTANE
FIGURE 1. DIAGRAMS OF CRYSTALS OF AMINEDILITURATES
DI ETHYLENETRIAMINE
INDUSTRIAL A N D ENGINEERING CHEMISTRY
536
ETHANOLAMINE
ETHYLAMINE
Voi. 15,
No. 8
ETHYLENEDIAMINE
1.592
n-HEPTYL -
HYDRAZINE
HYDROXYLAMINE
-n-PROPYLAMINE FIGURE 2.
METHnAMINB
PROPYLENEDIAMINE
DI.4GRAMS OF CRYSTALS O F AMINE DILITURaTES
the diagrams. The angle for a-methylhydroxylamine diliturate varies considerably; a value as high as 131' is frequently noted on lamellar crystals, whereas 109' is a good average for tabular crystals. Crystal angles for diliturates of propylenediamine and isopropylamine also vary a few degrees either may from those values recorded for each. Diliturates of 2-aminobutane, isobutylamine, and isoamylamine present irregularly shaped or broken ends. Occasionally the latter compound shows angles of approximately 138'. Cyclohexylamine diliturate possesses irregularly shaped ends, but 90' steps are usually noted. Hydroxylamine diliturate crystals are characteristically boat-shaped. Sometimes ammonium diliturate crystals are boat-shaped, but can easily be distinguished from hydroxylamine diliturate by means of the various constants given. Diethylenetriamine diliturate shows a definite cross-patching pattern or cleavage lines, especially in the thicker crystals, Hydrazine diliturate shows decided cleavage. The diliturate of 2-amino-n-octane exhibits slight cleavage. This compound occurs as masses of crystals which must be crushed to isolate individuals. Binary mixtures of amines (methyl and ethyl, methyl and n-propyl, methyl and n-amyl, isobutyl and n-butyl, ethyl and n-propyl, n-propyl and n-butyl) in equal proportions were used in preparing diliturates. The resulting compounds of the first four mixtures were composed of two types of crystals, each possessing the same optical properties as those exhibited when prepared from the pure individual amine; whereas the last two mixtures presented many crystals with properties other than those determined from the pure amines.
These compounds have been successfully used as unknon-ns for students in an elementary chemical microscopy course.
Summary The optical crystallographic data fo- 22 primary aliphatic amine diliturates and for dilituric acid have been determined. The optical properties provide a means of identifying pure amines and some mixtures of amines.
Literature Cited Ann., 127,209 (1863); 130,140 (1864). (1) Baeyer, .4., (2) Bartling, R., Ibid., 339,37 (1905). (3) Biltz. H., and Sedlatscheck, K., Ber., 57,339 (1924). (4) Ceresole, M., Ibid., 16, 1134 (1883). (5) Chamot, E. M., and Mason, C. TI'., "Handbook of Chemical Microscopy", 2nd ed., Vol. I, New York, John Wiley & Sons, 1938. (6) Ibid., Vol. 11, 1940. (7) Dermer, 0. C., and Dermer, V. H., J . Am. Chem. S O C 61, , 3302 (1939). (8) Elek, A., and Sobotka, H., Ibid., 48, 501 (1926). (9) Fredholm, H., Z. anal. Chem., 104,400 (1936). (IO) Grimaux, M. E., Ann. chim. (5), 17.278 (1879). (11) Hartman, W. W., and Sheppard, 0. E., 070. Syntheses, 12,58 (1932), h'ew York, John Wiley & Sons. (12) Holleman, A. F., Rec. trau. chim., 16,168 (1897). (13) Larsen, Junius, thesis, University of Colorado, Boulder, Colo., 1941. (14) Lauer, W. M., and Sunde, C. J.. Mikrochemie Preul-Festschrift. -. 235 (1929). (15) Redemann, C. E., and Niemann, Carl, J . Am. Chem. Soc., 62, 590 (1940). (16) Schlieper, A:, Ann., 56. 24 (1845). (17) Vogel, C., Ibid., 315,265 (1901). (18) Winchell, A. N., "Elements of Optical Mineralogy", Part I, New York, John Wiley & Sons, 1937.
