SILANES CONTAINING BROMINEIN SIDECHAINS
Aug. .?, 19.52
ture and the l,l-dichloro-l,2-dibromoethane* distilled at 175-177" dec., f l z 31.5554. ~ Pyrolysis of Acetylene and Trichlorosilane.-Cylinder acetylene, washed and dried, was bubbled (1' head) through trichlorosilane (40 8.) during 6 hr. and the gas mixture passed into the furnace at 610' to give a recovery of 23 g. Distillation gave some recovered trichlorosilane, 4.7 g of ~-inyltrichlorosilanc,b.p. 86-89', active chlorine ti4.8%, d,"" 1.23,and 2 S g. of more complex silanes boiling a t 180-217 . Pyrolysis of s-Dichloroethylene and Trichlorosi1ane.-A mixture of trans-dichloroethylene (42 g. ) and trichlorosilane (54 g . ) was pyrolyzed a t 610' during 600 min. t o give 80 g. of product. Distillation through a 12" packed column gave 36 g of recovered charge, b.p. 35-60', an intermediate cut, and the product, p-chlorovinyltrichlorosilane (19.9 g.) I, p. 133-135' (738mm.), nZoD1.4735,d2* 1.45. Anal. Calcd. for C2H2SiC14:3 active C1, 54.2; Si, 14.3. Found: 3 active C1, 53.3; Si, 13.6. The above product (14.5 9.) was treated with bromine (12.3g.) dropwise a t room temperature. Distillation gave a,P-dibromo-p-chloroethyltrichlorosilane, b.p. 131-133' (10 mm.) (22.2g.). Anal. Calcd. for C2H2SiCl,Br2: 4 active C1, 39.9. Found: 4 active C1, 41.2.
[CONTRIBUTION FROM
THE
3899
This brominated silane (22 g.) was hydrolyzed by shaking in about 50 cc. of cold water, and then excess base was added. Distillation gave a lower layer which weighed 6.4 g. after drying, and was accompanied by flashes of flame. Distillation gave 3.0 g. of 1-chloro-%bromoethylene,* b.p. 80-85', dao 1.8,rt"D 1.4956. Similarly, cis-dichloroethylene (22 9.) and trichlorosilanc (30 g . ) a t 610" gavc 13.7 g. of 8-chlorovinyltrichlorosilane, b.p. 132-134' (707 mm.). Bromination gave the same product as above and side chain cleavage with alkali also gave l-chloro-2-bromoethylene, b.p. 80-85" (1.8 g.), 1 2 2 3 ~ 1.4955, dZo1.8. Pyrolysis of Vinylidene Chloride and Trichlorosi1ane.--A mixture of vinylidene chloride (34 9.) and trichlorosilane (46 8.) was passed through the furnace a t 550' during 100 min. to give 62 g. of product. Distillation gave 48 g. of recovered charge, b.p. 31-35', an intermediate cut, and a product cut, presumably a- or i3-chlorovinyltrichlorosiiane, b.p. 115-135' (4.7g.). Redistillation gave 2.7 g. of product, b.p. 59-63' (63 mm.), n% 1.4610. Anal. Calcd. for C2HZSiClr: 3 active Cl, 54.4; Si, 14.3. Found: 3 active C1, 54.9; Si, 13.9. NORTHFIELD, MINNESOTA
DEPARTMENT O F CHEMISTRY, ST. OLAF COLLEGE']
Observations on Certain Silanes Containing Bromine in Side Chains BY COURTLAND L. AGREAND WALLACE HILLING RECEIVEDJANUARY 10, 1951 Vinyltrichlorosilane readily adds bromine to give a,P-dibromoethyltrichlorosilane. Pyrolysis of this silane is complex and among the products formed are silicon tetrachloride, trichlorobromosilane, a- and 8-bromovinyltrichlorosilanes and ethynyltrichlorosilane. The obtainment of silicon tetrachloride is unexpected for trichlorobromosilane only would be expected. Removal of hydrogen bromide from a,p-dibromoethyltrichlorosilane by treatment with quinoline gives a-bromovinyltrichlorosilane and silicon tetrachloride. Various transformations of the silanes encountered are described as their structures are determined mainly by side chain cleavage by alkali. Brief mention is made of the pyrolysis of a mixture of trihromoethylene and trichlorosilane.
Many examples have appeared recently showing that halogen atoms in the side chains of substituted trichlorosilanes encourage side chain cleavage with the net result that a halogen atom from the chain seemingly has become attached to the silicon atom. This research deals with the reactions which are encountered when bromine is present in the side chain, as in a,p-dibromoethyltrichlorosilane. Hurd2 treated a- and p-chloroethyltrichlorosilanes with quinoline to prepare vinyltrichlorosilane and obtained also a small amount of silicon tetrachloride. The reaction presumably progressed qualitatively as expressed in the equation Quinoline ClCH2CH2SiClS ------+ CH2=CH2 Sic14
+ + CHZ=CHSiClo f HCI (1) Sommer, Bailey and Whitmore3 later observed similar results on other silanes when cleavage was effected by heat, aluminum. chloride or methylmagnesium bromide-in these reactions i t was postulated that the reaction proceeded through the formation of @-carboniumions. Like Hurd, these authors also observed that silicon tetrachloride accompanied the vinyltrichlorosilane in the dehydrochlorination by quinoline of pure P-chloroethyltri(1) This research was conducted under Contract N8 onr 73700 of the Office of Naval Research. (2) D. T. Hurd, THISJOURNAL, 67, 1813 (1945). (3) L. H . Sommer, D. L. Bailey and F. C. Whitmore, i b i d . , 70, 2869 (1948).
chlorosilane. The preponderance of dehydrohalogenation relative to p-elimination (to give silicon tetrachloride) is suggested to be due t o the inability of the quinoline to provide a nucleophilic anion and also to the formation of quinoline hydrochloride. Parallel reactions with other substituted silanes were observed by Sommer, Tyler and Whitmore, and by Gold, Sommer and Whitm0re.j By similar reasoning, i t would be expected that a , P-dibromoethyltrichlorosilane (11)) for example, would decompose thermally to give vinyl bromide and trichlorobromosilane by &elimination, and a bromovinyltrichlorosilane and hydrogen bromide by quinoline dehydrohalogenation. Actually, in the pyrolysis of this silane dehydrobromination to give some ethynyltrichlorosilane and a mixture of a- and ,%bromovinyltrichlorosilanes is encountered to a major extent. Accompanying this reaction, however, is a side reaction in which silicon tetrachloride and trichlorobromosilane are both obtained. Another complex reaction was encountered in the dehydrohalogenatioh of I1 with quinoline for accompanying the a-bromovinyltrichlorosilane was an appreciable amount of silicon tetrachloride. Other similar examples are shown in the Aow sheet. (4) L. H. Sommer, L. J. Tyler and F. C. Whitmore, i b i d . , TO, 2872 (1948). ( 5 ) J. R . Gold, L. H. Sommer and F. C. Whitmore, { b i d , , 70, 2874 (1948).
CT-I,==CHBr
CI-IBr?CHBrSiCl3
+
\ l
j Rr:
CHpBrCBr?SiCl? \-I I
' quinoline
+
' 1I
BrCH=CBrSiCI? S
I
630 O j
+
CHlBrCHRr? IlrCII==CI3rSiCI (SI) i I
