Jan., 1951 [CONTRIBUTION
PREPARATION AND REACTIONS OF DICHLORODIFLUOROSILANE No. 284
FROM THE CHEMICAL
DEPARTMENT, EXPERIMENTAL STATION, E. I. DU COMPANY ]
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NEMOURS AND
Preparation and Reactions of Dichlorodifluorosilane * BY R. V. LINDSEY, JR. I n view of the differences in behavior of silicon fluorosilane, together with traces of butyl silicate, tetrachloride and silicon tetrafluoride toward were isolated.12 In view of the observation of Emcertain reagents, for example, alcohols, it was of eleus and Heallo on the disproportionation of diinterest to determine whether these differences ethoxydifluorosilane, it appears probable that the would manifest themselves in the mixed halide, primary product of the reaction of dichlorodifluorodichlorodifluorosilane. Selective replacement of the silane with n-butyl alcohol is dibutoxydifluorochlorine atoms in the mixed halide should provide silane and that the other products are formed by a direct synthesis for a number of compounds of the disproportionation. Although it has been reported that mercaptans general formula R2SiF2 (R = alkyl, alkylthio, alkoxy, the thio etc.) which have hitherto been difficultly accessible. do not react with silicon tetra~hloride,'~ During the course of this work, a new synthesis orthosilicates are obtained when the alkali me tal for the chlorofluorosilanes was developed. These mercaptides are emp10yed.l~ No reports on the halides have previously been prepared by the behavior of mercaptans toward silicon tetrafluoride explosive reaction of chlorine with hexafluorodi- have been noted. With dichlorodifluorosilane, it silane' and by the Swarts reaction from silicon was found that the alkali metal mercaptides react tetrachloride and antimony trifluoride. Since smoothly in the cold to give good yields of the neither method appeared suitable for large-scale previously unknown bis-(alkylthio)-difluorosilanes, laboratory preparation, attention was turned to the (RS)&iF2. Thus, with sodium ethyl mercaptide, redistribution reaction by which the bromo- bis-(ethy1thio)-difluorosilane and some tris-(ethylchlorides3 and fluoroiodides4 of silicon, and the thio)-fluorosilane were obtained. These comchlorofluorides6 and bromochlorides of phosphoruss pounds, like the oxygen analogs, are rapidly have been obtained by heating a mixture of the hydrolyzed by water. The behavior of dichlorodifluorosilane toward corresponding homohalides. It was found that the chlorofluorosilanes can be Grignard reagents was also of interest since silicon conveniently prepared by passing a mixture of tetrachloride reacts to give the series R4-,SiClX, silicon tetrachloride and silicon tetrafluoride whereas with silicon tetrafluoride the main product through a silica tube packed with broken porous is usually of the type R$3iF.l6~l7 From the replate heated to about 800'. The product nor- action of dichlorodifluorosilane in ether with 2 mally consists of a mixture of all of the possible mixed moles of n-propylmagnesium bromide a t - 7S0, halides and of unchanged reactants. However, there was isolated mainly dipropyldifluorosilane, i t was possible to obtain a high conversion to the some dipropylchlorofluorosilane, and higher boiling dichlorodifluorosilane by a combination of frac- products from which no pure individuals could tional condensation and recycling techniques as be isolated. The preponderance of dipropyldidecribed in the Experimental section. By a simple fluorosilane in the product indicates that selective low-temperature distillation, pure dichlorodifluoro- reaction of the chlorine atoms does occur. silane was readily obtained in good yields. Experimental The reaction of dichlorodifluorosilane with alcohols was of particular interest since silicon tetraPreparation of Dichlorodiiluorosilane.l*-The apparatus chloride reacts readily to give esters of the type is shown in Fig. 1. Silicon tetrafluoride (368 9.) was bubbled through silicon tetrachloride (550 9.) warmed to (R0)~xSiC1x,7 whereas no well-defined products about 50" and the mixed vapors passed through a silica have been reported from silicon t e t r a f l u ~ r i d e . ~tube ~ ~ packed with broken porous plate heated t o 830" in an Esters of the type (R0)4-,SiFx have been obtained electric furnace (A). The exit gases were passed through by fluorination of the corresponding chloro com- a vertical condenser (B) maintained a t -30 t o -35" and the condensate, consisting mainly of trichlorofluorosilane poundsl0or ethyl orthosilicate. l1 and unchanged silicon tetrachloride, returned directly t o The reaction of dichlorodifluorosilane with n- the mixing chamber through tube (C) which dipped below butyl alcohol in dry ether a t -78" gave a mixture the surface of the silicon tetrachloride. The vapors were of products from which approximately equal led to the botto? of a second vertical condenser (D) cooled to -60 to -65 . The condensate (540g.), which was rich amounts of dibutoxydifluorosilane and tributoxy- in dichlorodifluposilane, was collected in the receiver (E)
*
Presented before the Division oi Physical and Inorganic Chemis try at the 118th Meeting of the American Chemical Society, Chicago, Illinois, September 8, 1950. (1) Scbumh and Gamble, THISJOURNAL, 64, 3943 (1932). (2) Booth and Swinehart, ibid., 67, 1333 (1935). (3) Forbes a n d Anderson, ibid., 66, 931 (1944). (4) Anderson, ibid., 71, 2091 (1950). (5) Booth and Bozarth, ibid., 61, 2927 (1939). (6) T. Mitobedzki, Chem. List?, 16, 458 (1932); C. A . , 17, 476
(1933). (7)Friedel and Crafts, Ann. chim. phrs., g, 11 (1866). JOURNAL,68, 786 (1936). (8) Gierut, Sowa a n d Nieuwland, THIS (9) Tarbutton, Egan and Frary,
