X-Ray Diffraction Patterns of Solid Aromatic Hydrocarbons L. J. E. HOFER
AND W. C.
PEEBLES
Ofice of Synthetic Liquid Fuels, Bureau of Mines, Brucaton, Pa.
For the positive identification of solid crystalline aromatic hydrocarbons, x-ray diffraction analysis is proposed. X-ray powder diffraction patterns of 59 hydrocarbons have been obtained using iron-target radiation. Impurities sufficient to lower the melting point by as much as 15’ C. do not appreciably modify the diffraction patterns. The patterns are very characteristic; those of closely related compounds and even isomers are unique and can be readily identified.
I
NVESTIGATIONS into the basic aspects of coal hydrogenation a t this laboratory have led to the preparation of a series of highly purified solid aromatic hydrocarbons that are of interest to the coal tar, dye, plastics, fuel, and other industries. The well-known relationship of euch compounds to carcinogenesis makes them especially interesting in the field of medicine. Aromatic hydrocarbons of high molecular weight are often difficult to purify, resulting in tedious and difficult identification by melting point. I n some instances-for example, periflanthene-the melting point is unattainable. X-ray diffraction patterns of relatively impure aromatic hydrocarbons, however, are characteristic. Even minor modifications in structure produce almost
Table I.
completely different powder diffraction patterns. To take full advantage of the possibilities that x-ray diffraction offers as a method of identification of micro samples, a device for preparing extruded specimens from very small samples (2 to 3 mg.) using no permanent binder has been developed ( 1 2 ) . Thus, x-ray diffraction offers a completely nondestructive method of microanalysis. PROCEDURE
A modified form of the technique employed by McKinley, Nickels, and Sidhu ( 1 4 ) was used. A finely ground sample con-
Melting Points and Three Most Intense Diffraction Lines of Aromatic Hydrocarbons (Arranged in order of first lines)
Pattern NO.
54 50 22 38 29
58
Three Strongest Lines 2nd 3rd 1st 8.0 10.9 3.96 10.5 4.01 3.63 5.3 8.4 5.85 3.71 8.3 3.27 4.12 8.1 6.6 4.70 6.0
{::E
17 49
5.6 5.4
4.51 3.68
5.4 10.9 3.98
1:;
5
5.3
4.15
12 31 16
5.3 5.2 5.2
3.45 5.8 3.98
28 2 33 42 55 56 9 40 48 26 30 32 39 7 45 15
5.1 5.1 5.0 5.0 5.0 4.97 4.93 4.88 4.88 4.88 4.86 4.86 4.80 4.76 4.74 4.72
3.67 3.49 12.1 3.98 3.39 13.4 3.36 4.51 3.95 3.39 4.62 4.33 3.81 3.77 4.38 3.48
23 10 27 25
4.71 4.68 4.68 4.67
3.86 5.1 4.11 5.4
3.23 7.3 3.36 4.25
Melting Points, O C. Literature Founda 255.7b 257 (7) 9 1 . 4 t o 92.4 ( 8 1 ) 9 1 . 4 t o 92.4
Dibenzo [cd,jk]pyreneC 5-Ethylchrysened
135.2 t o 135 7 (83) 100.5 (11) 147.5 to 148.5(1)
135.2 t o 1 3 5 . 7 101.6 t o 1 0 1 . 9 1 4 8 . 8 to 1 4 9 . 4 142
4,s-Dihydropyrene e Bimmitvlf . 4-3fethGlpyrene E
76 ( 1 ) 128.6 to 129.8(21) 46 t o 47 ( I S )
7 7 . 2 t o 78 2 128 6 t o 129 8 4 5 . 6 to 4 5 . 8
45 ( 7 ) 6 7 . 5 t o 6 8 . 5 (6) 73 t o 74 (7)
44.8to 45.6 68.9 to 70.4 7 2 . 0 t o 73.0
9.3 4.31 4.18
{$!i
1 2 4 . 5 (7) 95 ( 7 )
1 2 6 . 8 t o 127.4
3.93 12.1 13.6 3.65
1 5 9 . 5 t o 160.5(7) 2 1 5 . 5 to 2 1 6 . 0 (18) 364 ( 3 ) 281.6 t o 252.2 (22) 1 0 0 . 7 t o 101 (7)
158.0 to 159.0 2 1 7 . 0 t o 217.4 36G.0 t o 3 6 7 . 0 2 5 4 . 5 t o 255.0 9 8 . 8 to 99.8
4,625 4.10 3.68 11.75 10.7 9.8 3.84 4.12
1 6 1 . 0 t o 161.4 (10) 196.6 t o 1 9 7 , 2 (88) 189 t o 190 (7) 5 5 . 5 (11) 4 5 . 7 to 4 8 . 0 ( 8 ) 1 1 7 . 2 t o 1 1 7 . 8 (21) 46 t o 47 (10) 79 t o 80 (11) 103 t o 105 (7)
1 6 1 . 0 to 196.6 to 185.4 t o 54.3 to 45.7to 117.2 to 53.8to 76.4 to 99.8 to
1 0 2 . 5 (16) 108,5 (7) 208 t o 2 0 9 46 ( 6 )
102.2 t o 1 0 3 . 8 108.6 t o 109.6 213.0to214.2 47.0to 47.8
{3E. 8L 7
93.2 to 93.8
(7)
‘ Corrected. Decomposed. Synthesized b y M
a
Orchin Bureau of Mines. Donated and synthesized 6 y M. S. Newman, Ohjo S t a t e University. Donated by M. S. Newman, Ohio State University. I Synthesized b y L. Reggel, Bureau of Mines. 0 Donated by J. E. Nickels, Mellon Institute. h Donated by Bureau of Mines. e
690
161.4 197.2 186.0 55.3 48.0 117.8 54.2 77.4 100.6
Compound
2,2‘,7,7’-Tetrarnethyl-l, 1’binaphthyl e
1,4-Di-tert-butylhenzenen 5,G-Dirnethylchr~sene~ 2,2’-Dirnethvldicvclopentylh 9-1Zlethylfluorene 1-o-Tolyl-naphthaleneh
1,2,3,4,5,6,7,8-OctahydroanthraceneC 3,4-Benzofluorene Acenaphthene i
1 2-Benzanthracene j 8:9-Benzofluorantheneh Piceneh hlethylpicened Phenanthrene i
V O L U M E 23, NO. 5, M A Y 1 9 5 1
691
taining no binder was partly extruded from a 0.75-inch tube of 19-gage, stainless-steel tubing having a n inside diameter of 0.7 mm. The detailed method of sample preparation is described in another paper (12). Each specimen was exposed in a 114.6-mm. diameter, DebyeScherrer camera for 6 hours in order t o obtain the long spacings (up t o 19 4.)in the low angle region; the sample was overexposed in a 57.3-nim. diameter, Debye-Schemer camera for 2 hours to bring out the shorter spacings in the larger angle region of the diffraction pattern. Long TTave length radiation (FeK,, X = 1.937 -1.) n-as obtained from a commercial sealed-off x-ray tube equipped with an iron anode, beryllium windon-s, and manganese oxide filters. I n choosing ci method for measuring the diffraction patterns of organic crystalline compounds for identification purposes, the following considerations are important. I n general, the patterns of these compounds exhibit strong reflections only a t small Bragg angles (6545 ") even when long wave-length radiation (CrII, or FeII,) is used in producing the powder patterns. This effect is related t o the fact that the amplitudes of the thermal vibrations of the atoms in organic molecules arc a large fraction of the crystal spacing, d , when d is sniall-t,hat is, n-hen e is large. The width of the diffraction lines is exactly equal t o the specimen width if parallel radiation is used and if little or no absorption takes place in the specimen ( 2 4 ) . But neither of these conditions is actually met generally. Divergent radiation broadens the lines in the region ~ 4 5 and ' n a r r o w the lines in the region 8>45". Inasmuch as the patterns studied herein w r e found only in the region 0(45', only the broadening effect need be considered. The effect of finite focus size is to broaden the lines in all regions. Because of the efficient centering system, the
Table I. Pattern
broadening effect resulting from eccentricity is so small as to be negligible. Finally there is the absorption effect which tends to shift the point of maximum density toward larger values of e and toward smaller values of d. The absorption effect increases with the product PT where p is the absorption coefficient and T is the specimen radius. I n the present study IJT = 10 reciprocal cm. and r = 0.035 cm. Thus, PT is 0.35 and is large enough t o produce a small but definite shift of density maximum (2.4). The following are several methods of measuring the arc corresponding t o the angle 48: ( a ) measurement of the distance between the densest portions of corresponding lines; ( b ) ineasurement of the distance between the outside edgc of one line t o the inside edge of the corresponding line; ( c ) nieasuremerit of the distance betlveen the outsides of the tn-o Corresponding lines and subtraction of the specimen width from thc dietance. Method (a)produces maximum systematic errors in the region e
