J. F. HYDE,L. K. FREVEL,H. S. NUTTING,P. S. PETRIE.4ND A I . -1.PURCELL
488
[CONTRIBUIIO V FROM THE
RESEARCH LABORATORIES O F CORNIXC GLASS\ r O R K S
ASD
THEI)OlV
Vol. B!)
CHEMICAL COMPAYY.]
Cyclo-diphenylsiloxanes BY J . F. HYDE,'L. K. FREVEL,~ H. S. NUTTING,'P. S. PETRIE?AND 11.-4. PURCELL~ The marked tendency of di-organosiloxanes to assume cyclic structures was demonstrated by the early isolation of a hexaphenylcyclotrisiloxane, [ (CeH&Si0]3,3a.'bmelting a t 18S0, and an octaphenylcyclotetrasiloxane, (CsH&SiO] 4, 3b melting a t 201' (for convenience these are hereafter called trimer and tetramer, respectively). Kipping and RobisonYcshowed t h a t the trimer crystallized in the orthorhombic system and the tetramer in the triclinic (anorthic) system. They first encountered the variations in melting points and appearance of crystals along with low molecular weight values, which have been a source of difficulty in subsequent investigation^.^ [(c~H&Sio~ 3 l
I d
Orthorhomtiic
is identical with that described by Kipping.3c The second, 113, is triclinic. Each form melts a t 187-18s' and there is no lowering in melting point when they are mixed together. Diagrams of their crystalline appearance are shown in Fig. 1 , The two forms have been obtained sitnultaneously upon crystallization from ethyl acetate in large enough crystals so t h a t they could be separated by hand. Is is converted to I I j upon resolidification of molten 13. The tetramer has been found to exist as a crystalline substance, -q4, containing two moles of tetramer t o one of benzene and as three solventfree crystalline polymorphs 1 4 , 114 and 1 1 1 4 . [(Ci")&Ol4
113 It 114 Triclinic Triclinic Monoclinic Fig. 1.-Crystal habits of trimer and tetramer.
2 [(C6H&SiOl ~ . C ~ H F ,
A4 Llonoclinic
Such variations have been observed by the Diagrams of their crystalline appearance are authorssh during the past four years but i t was shown in Fig. 1 and a diagram indicating their not until X-ray methods were applied t o the prob- transformations from one t o the other is shown in lem that it was fully appreciated that these varia- Fig. 2 . 1 4 is triclinic and its crystal measurements tions are due t o polymorphism, solvent of crysalmost exactly with those given by tallization and eutectic formation. B ~ r k h a r d ~ ' ,correspond ~ and co-workers have also used X-ray techniques K i ~ p i n g . ~ ~ and have described one of the new tetramer 111is monoclinic and is the material described polymorphs. by Hyde and D e L ~ n g . I~t ~is also identical with I t has been found that certain of the poly- the inaterial described by Burkhard and comorphs may be changed to others a t will but due workers with the exception that the crystals to their similarity and instability the procedures were clear and not opaque as described by the presented are not t o be considered infallible. latter authors. This has been confirmed b y XNo attempt has been made to work out complete ray examination of the original crystals erroncously described by the-former as a trimer melting phase diagrams. a t 200' and by simultaneous X-ray examination Polymorphism The trimer has been found t o exist in two crys- of a recent sample with one which was kindly talline forms. The first, 1 3 , is orthorhombic and loaned by Dr. Burkhard for the purpose. 11and 1 1 4 and their mixtures melt a t 200-2001'. They (1) Corning Glass Works. are stable a t room temperature o w r a period of ( 2 ) The Dow Chemical Company. years. ( 3 ) (a) Dilthey, Bey., 38, 4132 (1905); (b) Kipping, J . Chem. Yo( ,. 101, 2 3 2 5 (1912); ( c ) Kipping and Robison, ;bid., 105, 481 1 1 1 4 melts a t IbX', the same point AS the trimer, ( 1 9 1 4 ) ; k r l ) Hyde and DeLong. THISJ O U R N A L , 63, 1194 (1941), and is quite unstable, changing over t o I4 a t room Burkhard. ihi.1.. 67, 2173 (1945): ( f ) Burkhard, Decker a n d temperature in a matter of a few hours. Conliarker. ? h i d , 6 T , 2174 ( 1 9 4 . 5 ; (g) Kipping. Chcm. I d . , l(i8 versely, Ii is converted to 1111by cooling its inelt (19t.j); (11) k y d c , i b i , / , , 270 (10.4.j). IC)
4S!)
+
:With loss "r
111,
M.
I).
t
lXXO
C.II~.
slowly or by holding the crystals a t 100" lur :ibout a n hour. llixtures of I4 aud I l l l souietinics uwlt gradually over the entire rangc between ISS and 2001 and at other times thcy iuclt rclativcly sharply at some iutcrinediate point. I l l n is also formed by cooling the molten 114 slowly, but the corrrsponcling change a t 1 0 0 O docs not seem to take place. A4 can be obtained a s large truisparent uiomclinic crystals which arc quite stablc when held in the mother liquor or i n a small closrd container. \\;hen thesc are subjected to conditions under which the benzene may escapc, the crystals retain their original size and shape but becornc opaque and the X-ray shows that they havc changed t o polycrystallinc I & (see Fig. 3 ) . The saiue change takes place rapidly upon grintliug to a fine powder.
X-Ray Investigation In view ( ~ fthe fact that niost of thc molecular wright detcrniinations o n the trinicr iuid tetramer (see l';ible 11') gi\~einilccisi\rc v;ilurs, i t was decided to invcstigatc tlic ~)rol,lciii by X-ray diffractioii uicthcrils. 'l'hc procedure followed p~i~'iIIcls that reported by I3urkhard, Decker :iuiI Hwkcr?" I3olh Lair ani1 ciscill;itioii photographs wcrc used to determine tlic unit ccll dinicusions. The clcnsity valuc for 11, o f l.l!lS g.:cc. is belic\~cdto be quite accurate, since it was di~terniiiicdOII a clear crystal specimen (O..> X 1 .X 3 iuni.). This density givcs a valuc uf I>.X:3 i n o u ~ ~ m euuits r per unit cell :is compared with the \ d u e 15.52 showu by I3urkharrl. This valuc 01 I5.S:l rcprcsents an intcgcr which is sulliciciitly clmcr ti) I ( i than t i J 13, t i l w:irrant the colic~us~oll that I ( ; is the rei1 d u c to he e i u p l ~ ~ y ~ :\ccordingly d. there :ire ( l l i * l . v ) [(C6H5)2SiO]x ~ur~leculcs in thr unit ccll where s iiud Ilils have tu bc integers. This rcquireiiient uuiqucly excludes the trimer forinula inasmuch a s :3 is not an integral factor of lti. Since cryoscopic data preclude .x = 2 or S. the crystalline substance 111 c u i be cli:micti,rizi~I ~ ~ I 111I . I ~ .iiiglv ~ ~ Icry.i:~l ~ . ~ cd~ 2;(C,,ll ~ ~ ~ ,l:Si(I;,.C,,l I , , ii.trli;tlly ,irrcm>IIow~/.'I'INI:,yw l i n ~ v
