T
.
HIS is the secondinaseries ofmonthlysummaries of crystallographic data. The first paper [ANAL.CHEM. 20, 274 (1948)l covered the organization of thie project, the conditions for cooperation by outside organizations, the conventions to be used for crystallographic descriptions, and orystallographic data for the two polymorphic forms o f p,p'-DDT.
2. Adipic Acid Well formed crystals of adipic acid (hexanedioic acid) can he, ohtitined from ethyl ctcetaee. Crystals from water either macroscopically or on a microscope slide are not well formed, although they are recogniaable as basal pinacoid tablets elongated parallel to b. The crystalsfromsuhlimtLtiononamioroscopeslide are well formed and usually give rhombs lying ou the basal piuacoid (Figure 1). There is no evidence from either the thermal work or recrystallization that adipic acid exists in more than one polymorphic form. CRYSTAL MORPHOLOGY (determined by A. w. c.
McCronei.
IJ
d 6.82 4.67 4.49 4.13 3.79 3.52 3.45 3.31 2.86 2.53 2.51 2.41 2.32 2.26 2.19 2.14
oii;oii 101 200 002
...
210 020 201
an
300 on3
...
2.m
220 022 505
2.04 1.92 1.87 1.80 1.76 1.71 1.50 1.46 1.42 1.40 1.28 1.24 1.22
202
322 400 004, 030 222 420 024 500 040 402, 303 240
1906.
3. trans-Azobenzene
_.
~
I/I, 0.41 0.02 '0.02 1.00 Very voak Very weak 0.31 0.05
o.14
Very weak 0.07 0.07
0.10 0.08
o.oe
0.08 Very v e a k Very weel. Yery weak Very weak Very weark Very weak Very weak Very weak Very weak Very weak very weal Very weak Very weak Very weak
.~~~
inilined dispersion, v
Excellent crystals of aaoheneene can be obtained from alcohol and ethylacetate, by sublimation or on a microscope slide by recrystdlization from thymol. For most puqmses the sublimed Figure 1. Crystals of Adipic Acid Formed by Sublimation on a Microscope Slide
OPTICALPROPERTIES (determined and checked bv A. Smedal
Uisuersion. V&sl&htly
LITERATURE CITED
(3) MaoGillavry, Rec. trao. chim.. 60. 605 (1941).
Principal Line.
Index
~
Caspari, J . C h m . Soc.. 1928, 3235. (2) Groth. "Chemisohe Kristallographie," Vol. 3, p. 465, Engelmann,
.
~ ~
(+y,
(1)
Crystal System. Monoclinic. Form and Hahit. Tablets from ethyl acetate elongated elaxigated parallel to b with well developed basal pinacoid 1001); I001 I ; other forms present are: prism 13201, orthouinacoid 11001. 11001 and occasionally the clinopinacoid 1010). Axial Ratio. a : b : e = 2.014:1:1.5 Interfacial Angles (Polar). 100111 52 48'. Beta Angle. 137"5'; (137"5')(8)). X-RAY DIFFRACTION DATA(deter, _..__.._I Corvin and J. Whitney). Space Group. C t ( P 2 , l a ) (5'). Cell Dimensions. a = 10.27; b = 5.10; c =. 10.02. (a = 10.07: b = 5.16: e = 10.00). (Si. (a . . . = 10.27: b = 5.16: c = 10.02j ( 1 ) . Formula Weights per Cell. 2; (2) (I,S ) . Formula Weight. 146.14. Donsity. 1.344 (measured by flotation and pycnometer); 1.37 (calculated).
_....
Optic Axial Plane. 010. Acute Bisectrix. y. Extinction. yAe = 3 " in acute 0. Si-n of Double Refraction. Positive. Molecular Refraction (Ri. . . R (caled.) = 32.97. R iahsd.) = 33.00. THERMAL DATA(determined by W. C. McCrone). 1. Adipic acid sublimes readily just helow the melting point to give well formed rbomhs lying on the basal pinacoid and showing an almost centered optic axis interference figure and a profile angle of 54". 2. Melting occurs a t 151-153' C. with no decomposition: the melt erystdizes on cooling with only slight supercooling. Sharp pointed rods grow rapidly to form feathery crystals; the growth rate increases 8s the temuerature falls to room temperature. 3. All three principal views can he ohtainea; shrinkage cracks and interference figures are characteristic of each view (Firmre 2). An almost centered outic axis fieure shows 2V = 76". with very slight dispersion, > I. 4. Adipic acid is almost insoluble in thymol, although crystals in the zone of mixing during a mixed fusion show a profile angle of 44", parallel extinction and one index less than the thymol mclt.
> 1. 385
Figure 2. Fusion Preparation of Adipic Acid Crossed Nicols
ANALYTICAL CHEMISTRY
386
c
Formula Weight. 182.22. Density. 1.220 * 0.001 (1.22) (1). oo
Pripcipal Linea d 7.03 5.59 5.33 5.12 4.88 4.62 4.54 4.47 4.30 4.18 4.02 3.82 3.75 3.67 3.51 3.39 3.29 3.19 3.09 3.00 2.88 2.80 2.68 2.57 2.51 2.46 2.34 2.27
Index 002 200 011 110
...
003 111 012
... ... ...
210
300 202 004
... ... ... ...
a-c
.
02b 005, 400 022 220 204 303 006
222
Figure 5. Orthographic Projection Showing Principal Views of Adipic Acid a.c
c
Red Blue 5893
,CG
Figure 6. Orthographic Projection Showing Principal Views of Azobenzene
crystals are most satisfactory; no evidence of the existence of polymorphic forms of azobenzene was obtained. Azobenzene has been set up differently from the orientation reported in the literature (1, 2 ) . The reorientation involves reversing the a and c axes to follow the convention c < a. -4lthough this change is made with reluctance we feel that any convention based on crystalhabit is impractical, as habit depends on so many factors other than cell dimensions-e.g., solvent, temperature, impurities, etc. If the convention a -=? c, rather than c < a,had been chosen the orientation of adipic acid would have had t o be changed. CRYSTALMORPHOLOGY (determined and checked b j IT-. C. McCrone and J. Cook). Crystal System. Monoclinic. Form and Habit. Usually tablets lying on the orthopinacoid { ! O O ] , slightly elongated parallel to b. Other common forms are clinodome [ 011 },orthodomes { 302 1, and the basal pinacoid { 001 1. Axial Ratios. a:b : c = 2.676: 1 :2.114 (calculated from x-ray data). 2.662: 1 :2.108 (calculated from goniometry) ( 2 ) . Interfacial Angles (Polar). 011h011 = 5 5 " ; 302A100 = 50". Beta Angle. 114"; (114' 26') (2). X-RAY DIFFRACTIONDATA (determined and checked by J. Whitney and I. Corvin). S ace Group. CL, (P2Ja) (1). &ll Dimensions. a = 15.40; b = 5.77; c = 12.20. (a = 15.40 * 0.04; b = 5.77 * 0.02; c = 12.20 * 0.04) (1). Formula Weights per Cell. 4; (4) ( 1 ) .
0.07
1.00 0.05 0.44 0.92 0.41 0.04 0.17 0.10 0.58 0.50 0.49
0.08 0.04 0.10
0.23 0.25 0.12 0.07 0.04 0.17 Very weak Very weak Very weak Very weak Very weak
OPTICAL PROPERTIES (determined and checked by IT;. C. Mc- ' Crone and J. Cook). Refractive Indices (5893 d.: 25" C.). LY = 1.706 * 0.005. p = 1.720 0.008. = 1 . 8 5 ' 1 0.02.
I
y1
I/Il 0.25 0.12
Optic Axial Angles 2v 27O 880 490 64' (59.5) (1) 36" 2E 480
A.
2H 31O 640 41' (39'21') ( 1 )
Dispersion. Very strong horizontal dispersion of the optic axial angle, u > r; very slight dispersion of the optic axial plane. Optic Axial Plane. 1 0 1 0 with y h c = 7 " in obtuse beta. Acute Bisectrix. y . Sign of Double Refraction. Positive. Molecular Refraction ( R ) . R (calcd.) = 59.71. R (obsd.) = 62.26. Pleochroism. Very light yellow ( X ); orange ( Y ); and deep orange ( 2 ) . THERMAL DATA(determined by W. C. McCrone). 1. Azobenzene melts at 68" C. with no decomposition and only a slight tendency toward sublimation. The melt always crystallizes spontaneously and very rapidly; the rate increases as the temperature falls. 2. The crystal front is angular, usually with a profile anglt of 50". This view shows y and p with oblique extinction of 7 and an obtuse bisectrix interference figure. Figure 4 shows a completely crystallized fusion preparation of azobenzene. 3. Azobenzene is very soluble in thymol and can be crystallized from this solvent (Figure 3). A thymol mixed fusion gives good profile angles; 129", 115", and 155" are prominent with a flash interference figure. LITERATURE CITED
(1) de Lange, Robertson, and Woodward, Proc. Roy. Soc., 171A,398 (1939).
(2) Groth, "Chemische Kryatallographie," Vol. 5 , p. 60, Engelmann, 1906.
I Symposium on Spectroscopic Equipment. Polytechnic Institute of Brooklyn, Brooklyn, hi. Y., May 22. Symposium on Electron and Light Microscopy. .Armour Research Foundation and Physics Department of Illinois Institute of Technology, Chicago, Ill., June 10, 11, and 12. Symposium on Nucleonics and Analytical Chemistry. Division of Analytical and Micro Chemistry, Northwestern University, Evanston, Ill., Aug. 13 and 14. I
