In summary, it appears overwheliningly probable that the S and R data apply not to an alloy of approximate composition Na4Pb but to some other substance or substances as yet unidentifieri, ant1 possibly of uukriowri constitution and structurc We are grateful to the Ethyl Corporation for financial support, and to hIr. S.AT. Rlitzer aitd r h . H. Shapiro for valuable discussions. DEPARTMENT OF CHEMISTRY MASSACHUSETTS ISSTITUTE OF TECHXOLOGY CAWHRIDGE, MASS
The Reaction of Chlorosilanes with Benzaldehyde BY ALBRECHTZAPPEL RECEIVED FEBRUARY 28, 1965
Iiochow and Gingold' recently stated that they did not succeed in combining chlorosilanes with aldehydes, including benzaldehyde, to form siloxanes, even on boiling for 3-3 days, the starting products being obtained again in unchanged form. I n this respect I wish to report on work carried out on this reaction, though with different scope and aims. Silicon tetrachloride reacts with benzaldehyde on being allowed to stand a t room temperature, the reaction being expressed by the gross equation Sic14
+ C,H,COH +( S i C l ~ 0 )+~ GHaCHCI?
If Sic14 is allowed to stand together with benzaldehyde, after a few weeks these liquids which inis well show an increase in viscosity which is somewhat accelerated b y exposure t o daylight. Dernixing occurs in two phases after 2-3 months. This phenomenon is caused more rapidly a t elevated temperatures. Likewise, in the gaseous phase Sic14 reacts with benzaldehyde within the sense of the above equation. The lighter one of the two layers consisted chiefly of excess benzaldehyde and benzal chloride as well as a small quantity of chloropolysiloxane while the heavy phase consisted to the major part of chloropolysiloxane. The latter was obtained as a residue in the fractional distillation. 'The determination of the molar weight estimate resulted in values between lS00 and 2000. The chlorine values of these polysiloxanes, calculated on hydrolyzable chlorine, were correspondingly around 60m0 with the silicon values around 3FCC. The index n in the formula (SiCl,O), thus appears to be in the order of 1.5. ii-hile always an excess of benzaldehyde reacted with Sic&in all the cases examined, the reaction did not proceed beyond the formation of a chloropolysiloxane. I t appears to be probable, however, that the reaction will proceed to the formation of Si02 with sufficiently long periods of eyposure or more critical conditions. ;\s shown by orientating qualitative experiments, the reaction is not limited to S i c & but also proceeds in a corresponding manner in the case of organochlorosilanes, e.g., phenyltrichlorosilane. The reaction appears to take place in two stages. (1) I(1074)
G
Rochox,
and
h' (:m,rold
?HI5
Jol
R\IAl,
76, - i Y i ?
111 a first stage the Sic14 will add on tlic CO tloul)lt~ link of the aldehyde
I'I.ISiCl
+ OP-CIIC611i--d Cl.,SiOCIICICeIln ( 1 )
This product seeins to react, relatively rapidly with a further Sic1 link t o form CitSiOC€IC1C611~ j
.
CI.,SiOSiCl:;
+ C6HsCIICll
(2)
S o such products as result from equation 1 were isolated. The apparent discrepancy with respect to the work of Rochow and Gingold can satisfactorily be accounted for by these two authors only having tried triphenylchlorosilanes with benzaldehyde.' In the case of this silane the reaction is strongly inhibited for steric reasons, and the reactivity of the Sic1 linkages is unfavorably influenced by t h e three phenyl groups. This suggestion is supported by the observed fact that already the PhSiC13 reacts with benzaldehycl:. somewhat slower than SiCI,. ( 2 ) Private report b y Prof. E . G. Rochow
BAYERi\KTIENGESSEI,I,SCHA~T I ~ ~ ~ E R K ~ - s E N - B (:ERRIAUY . ~ ~ - ~ R ~ ~ , ~ ~ ~ , FARBENFABRIKEN
Phase Diagram of the System KSbO3--KTaO3by the Methods of Differential Thermal and Resistance Analysis B Y ARs0r.D
REISMAX,S O L TRIEBWASSER AKn HOLTZBERC RECEIVEDA P R I L 15, 1953
FRXnERrC
K N b 0 3 and KTa03both exhibit the BBOn perovskite structure, but have widely separated Curie points. The unit cell size of both compounds, in the cubic state, differs only slightly.' On the basis of this, and the isomorphic nature of tantalum and niobium compounds, a strong possibility for solid solution interaction between the meta salts was seen to exist. If such an interaction takes place, it might be possible to prepare dielectric ceramics with Curie points ranging between 13 and 68S°K., the Curie temperatures of KTaOy and KNb03, re~ p e c t i v e l y . ~Resolution ,~ of the diagram woukl provide needed information for the preparation ( i f the necessary ceramic materials. The solidus curve of a solid solution is generally more difficult to determine than the liquidus curve. The graphical extrapolation method employed by Tammann4 and later modified by Campbell and Prodanj was found inapplicable because of the difficulties in attaining reasonable equilibrium throughout the cooling range. The standard heating curve techniques are a t best laborious, and if not performed with the utmost care tend to gi\?e low results.6 If applicable, quenching methods are invaluable, but in this system the tendency fur crystallization to occur, even with small charges, (1) P. Vousden, Acta C y y s l . , 4 , 373 (1951). ( 2 ) J. K. IIulm, B. T. LIatthias and E. -4. L o n g , P h y s . X l v , 7 9 , 885 (19.50). ( 3 ) G. Shirane, H. Danner, A. Pavlovic a n d I< P e p i n s k y . i!'i,i., 93,
672 (19nO). (4) C. 'l'ammann, Z . Q E O Y ~ . C h e m . , 37, 303 (1903). ( 5 ) A S . Campbell a n d L. A . Prodan, T H I SJ O U K N A I . . 70, 5.-A (1'1) C, \T, l f o r e y , Jr., Il'ash. A i n d . (1.f Sii., 13, :lf; (19231.
(Ill
IX!
