CYANAMIDE, DICYANDIAMIDE, AND MELAMINE Optical and Crystallographic Properties T. G. ROCIIOW, K. W. STAFFORD, D. W. DAVIS, A N D K. I,. GILBERT American Cyanamid Conrpany, Slamford, Conn.
I W purpose of this i q i e r is l a jireseirt some rlescriptive and determinative microscopical data 011 tlre optical arid crystallograpliic properties of cyauamiile, iiicyandiamide, and melamirre. These compounds are of interest because they arc produced from calciiim cyanarniile, CaC the product of fixing atmosplierio nitrogen by means of lime and coke. Caic:iiiin cyanamide is tlieoret,ically a salt of cyanamide, which has been isolated iu a free state but so far has Id relat,ively little commercial applicatioii. It is very rcilotive and polymerizes easily to form dicyandiarnide
T
Some determinative optical data are presented for cyanamide, tL--C-, dieyan-
/NE&
, arid
diamide, HN--C
melamine,
\RHCN %I&
I N /-C\N
I
H,N-. -C
I/ "/
C-~~-N1i2.These three coin-
pounds can be produced from ealeium cyanamide, the produet of fixing atmospheric nitrogen by means of lime and mke.
priuciyal vicw uf the cryatals. These indices are of d e t e r m i n a t i v e value, but are not, necessarily c o r r e l a t e d with other optical or crystallugraphic directions. Tire data listed were obtained from laboratory sild pilot-plant samirles; commercial m a t e r i a l s may be ground, and thus n o t show c r y s t a l l o grapliic Faces. C Y A N A M I D EElon. ("rlicy"). This compound is fimiing cormrrercial use in the manufacture of resins. Uicy is also important in tlre commercial production of guanidine compounds which are used in explosives, rubber compounds, textile chemicals and dyestuffs, pharmaceuticals, and otlier industrial chemicals. Mclamiire is being used in moldiiig resins under the trade riame "Beetle-Melaniine" resins. Melamine is also being incorporated in renins for surface-coating enamels and varnishes, under the trade name "Melamac" resins.
The following optical data were determined by irriinersion metirotis, using tlie petrographic microscope. The refractive
0.003, on views showing parallel extinction; Na = ai~iiruxirnately 1.556, nTz = 1.675 * 0.003 on views showing oblique extinction. Maximum extinction angle, 10". Elongated crystals lengthen slowly. Biaxial (+). . . ,, 21.' estimated 30-40". r < u weak. Specific gravity (S), d:' = 1.073. Cvanamide is difficult to recrystallize, chiefly because it is so readily converted to its dimer, dicyandiamide. Figure 1 shows the shape of cyanamide crystals as they were
i n , l i ~ ~N~ .v N . ani4
nrirrinnllv menmad
Optical Data
.kJ..nnrraurumri t r i
mutinotinn
ilirwt,iona fnr
~'iounx:4. 'rHrlr CRYSTAL OF MELLMINE, S E I O W I N ~BASAL I'INACOID, IN TRANSMITTED LIGHT( X 100)
DICYANDIAMIDE. Six-sided plates, which are ixmnoclinic (2) prisms modified by diiiopinacuids and cliiiodomes. The usual view is the basal pinacoid which show-s symmetrical extinction (Figure 2 ) . The refractive indices, determined ia two ext.inction directions on this view, are: N , (81, 1.547 * 0.002; N,, approximately 1.630. This view gives a biaxial (+) optic axis interfcrence figure, 2V estimated 40-45", r < u moderate. The view of the clinopinacoid, shoving oblique oxtinction, has refract,ive indices IV,, 1.88 * 0.02, and A',, 1.547. Specific gravity (S), d14 = 1.40. Figore 3 shows a group of crystals of dicyandiamido, recrystallized from water. MEIAMINI,:. Simple monoclinic ( 1 ) prisms terminated by basal pinacoids, when recrystallized from water. The uaial view in thin crystals is the basal pinacoid, wlrich shows sym-
In transmitted light ( X 100) E'IGUXS
nietrical axtinction (Figure 4). The acute angle in this view is ahout 70", and the refractive indices, determined in two extinction directions, are: N,, approximately 1.670; Ns 1.86 0.03. The lowest refractive index, determined on fragments, was approximately 1.490(a). The symmetrical view gives an uncentered biaxial optic axis figure. Melamine is biaxial (-), 2V estimated as about 35", T < v distinct. Specific gravity (S), dz6 = 1.573. The crystalline habit of melamilie depends on the processes by which it is synthesized and crystallized. Figure 5 shows melamine recrystallized from water. The commercial material is usually ground and ordinarily shorn few crystallographic edges.
Li Lernture Cited (1) Beilrtein. Handbucti der organirehe Chenrie, Yol. I. p. 1443
(1893). (2) Dohiinper. U . . Z. Krisl.. 65, 286-80 (1927). (8) Lange. Handbok of Chemistry. 2nd od., 1837.
I n reficcted light ( X 15)
5. MELAMINE. 1
