AI. 31. SPRUNG .WD F. 0. G ~ E S T I I E R
3990
1) indicates that each compound shows its 0 ~ 1 1 ~wlarograpliicbehavior irrespective of the PH of the medium (Fig. 2). The diffusion currents obtained for the first wave of azoxybenzene a t the same concentrations (Tabks I1 and 111) change vcrv little when studied alone or in the presence of hydrazobenzene and indicate t h a t very little reaction occurs between the two cornpountls. ‘:‘he r c d t s for hvdrazobcnzene in geiicral sul)stnriti,ite tliis conclusion. Coli i ~ l i ~ a t i oh~ol ~~ e, ~ cnriw r , i i i coiii1xiri50x1s with this coinpound if traces of olvgeii cm present, since hydrazotien7ctie is \ ery casi1~-( > \ I dizecl t o ambeiizt-ne. The i)Iesence of the latter puts part of the polarographic ciir\’c o1)servcd for li? c l r ‘ ~ mbenmtie ,ilmvc thc 7ero line of the ,plvnrionicter (polarograms E and D in Fig. 71. The occurrence of such a reaction was fount1 o:ilv a t p€I 2.0 (47’;). 3.1 (19%), G.2 (12%) aiid 11 1 (2176). The coricentration of azoxybetizene in these buffers, as indicated hv the diffusion currents, was decreased signifi-
--]
y ’
A’
I
-0.5
-1.0 E d . e . DS.
I
-1.5 S.C.E., Volts.
Fig. 2.--Polarograms for cis-azobenzeiie, azoxybenzene anti hydrazobenzene in a buffcr of p H 5.1: A, cis-azobenzene; B, azosybeiizene; E, hydrazobeiizeiie; C, residual current ; D, mixture of hydrazoberizcie and azor!,beiizeile.
1’01. 77
cantly onl>7in the 1,uffcr of fiH11.1. Tlic coiiibiiicd CIITXX~ for liydrazobenzene and azobenzeric under these circumstances was not materially increased and points to some other reason for the decrease in current obscmwl. The po13rogra;’hic results obtained not only iiidirate that cis-axobenzene is a definite compound but :ilso preclude the occurrence of :i reaction 1ietn:er:l l~~,dr:izobenzt.ne uid azoxylwnzene i n the p1-I reqioil O i 2.0 t o 11.1 to for~iif r m s - or cis-azobenzcrie. ’I’he s!iift in hzll-wa\-e potentials of hydrazobeiizene in the prewiice of uzozyhenzene il1iistr;ites :lie sensitivitv c i i tliis svstein to tlic presence of maxi11111111 sripprvssors aiid otiicr coiiipo~.indsin the s o h timi. ’Thr polaroqralhic behavior of azoxvberizene in this work parallels t o a great extent the results reported r e ~ e n t l y . ~D u e to the more concentrated buffers employcd in this work the half-wave potentials when plotted against pH in the range of 2 to 7.5 gave a line with a slope of 0.081 v. as aqtinst the 0.1 v. r e p ~ r t e d . ~T n the PH range of 7.5 tu 11 the half-wave potentials were not coilstarit but s h o w 4 a slight increase with an increase iii PI-I. I n the present iiivestigation n second wave was obtained :it a pH 7.0 which was apprositnately equal to one 1i:ilf of the first w:.i\-e in height and pointed to the further reduction uf azoxybenzene to aniline. This wave appeared in the buffer of pH 3.0 but was complicated by the appearance of the atlsorption wave which has been found previously with hydrazobeiizene and cis- arid Imns-asobenn oiic a i 15 (19.531.
[ COXTRIBUTIOS PROM T H E GCXERAL ELECTRIC
R E S E a R C H LABOR.\TOKY]
The Partial Hydrolysis of Methyltriethoxysilane BY T\’x. h1. SPRUNG .\XD F.0. G U E N r I I E K RECEIVED SEPTEMBER 17, 1954 The action of three molar equivalents of water and catalytic amounts of acid 011 a benzene solution of inethyltriethoxysilane gave small yields of distillable liquids. These are principally cyclic polysiloxaties having both ethcxyl and hydroxyl “end groups.” I n alcohol solution, under similar conditions, onlv polynieric “methylsilicone gel” mas obtained. Using 50 or 25% of the calculated quantity of vater, complex inistiires of linear and cyclic products resulted. In the foriiier case, the t r o major products isolated are a monocyclic polysilo\r:tne (1,3,5,~-tetraethoxy-l,~~,5,7-tetramethylcyclotetrasiloxa1i~) and a closely related bicyclic structiim. 111the latter cas? the products are rniuture,>of the linear partial hydrolysis products, ~ t @ / C K r ( E t O ) S i O j , , Ewith t , minor atnotints of the cyc!ic Iroducts, ICHr(I?‘tO)SiO]., ivhere n is 3 t o 5. Under certairi conditions, it is possible to isolate sinal! amounts of sub1iin:ible solids having the composition, ( CI-12Si0,.5),,,where n is proh ably 6 and 8.
Introduction Trifunctional silanes of general structure RSiX3, \\,here R is an alkyl or aryl group and x is a functional group such as halogen, alkoxy or acyloxy, produce cross-linked polymeric structures LVhen hydrolyzed. Among organic silicon products, these structures are at present least well understood. Tile characterization of partial hydrolysis prod.. ucts of trifunctional silanes tvas unc1ertal.A u , generally nisociatcd rvith metllyic?i:lotetr;isil,iuini. r i n g s T h e r e is nn a b i u r l r t i o n v e a k a t 9 W . S i ‘ , I\ here h e s n I n e i ! ; ? i c p c l o t r ~ , , i ~ ~ s ~absorbs n~ strongly. O t h e r feature; of t h e c u r v e , however, >r.erc difficult t o i n t e r l j r c t . I‘herefnre, on th1.i basis alone, i t is not poisihle to concliide t h a t t l i e s t r i i r t u r e is entirely t h a t of 111, cxclusive of I I b .
Vol. 77
trimethyl-l,l,3,5,5-pentaethoxytrisiloxane (previously described by Fletcher and H ~ n t e r )and ~ 1,3,5,i - tetraethoxy - 1,3,5,7 - teiramethylcyclotetrasiloxane. Other fractions contained mixtures of homologous linear and cyclic polysiloxanes. I5‘ith 0.75 mole of water per mole of methyltriethoxysilane (this approximates the molar ratio of Fletcher and Hunter’s alkaline hydrolysis) the yiclcl IWS 100 g. of distillable oil from a 1-mole run. Redistillation into 39 cuts was effected, but onl!fivc of these represented the mid-points of welldefined ”flats.” .lnalyses indicated that only the lowest-boiling of the mid-cuts was pure; this W:LS the l i n e x dimer, 1 ,:3-dimethyl-1,1,3,3-tetraetlioxydisiloxane. ’The higher-boiling “flats” xvere of the straight-cliain polymer-homologs , 4, mid .5 silicon atoms, with the corig ~~olyethox~iiietliylcyclopolysiloxaiie~. Uiider alkaliiie hydrolysis conditions, Fletcher antl Hunter obtaincd these particular partial hydrolysis producis, free froni cyclic by-products. Total Hydrolysis Products.--The usual total hydrolysis product of a methyltrialkoxy or niethytrihalosilane, so-called “T-gel,” has the empirical composition (CH:$iOl.j:),?. I t is a granular, insoluble, infusible, 3 ntl generally intractable solid. Molecu1:ir weights have not been assigned to this tyi’e of pro,Iuct for obvious reasons. Tlie foriiiati~iiof ’T-gel freyueiitly is observed during ixirtid hydrolysis experiments. Sometimes sniall aiiiciunt:; d solids having the geueral appear~uicr.of ’T-gel Lire i‘oriiiul which, however, arc found to lie quite tlifferciit c i n closer exaniinatio~i. IfI-hereas ’Y-gcl can bc 1it.atetl ahc~ve250” in vacuum without appreciabltx physical change, slow sublimation could be accoinplished with several of these solid bypro(lucts under similar conditioiis. The sublimates usually did riot melt below 300”. In one experiment, lion-ever, the sublimable, high melting solid TWS accoiiipaiiiecl by a very small amount of a lower iiieltiiig (-210”) solid, from which it was separated I);*- fractiiin:il subliiiiation. The two conipounds 1i;iri t h e saiiw ctii1)irictll coinpositiou. I t is believed that the chief coinponelit of these high-iiieltiiig subliiiiates is the completely colitlerisctl, cage-like molecule having eight silicon atoms, with one methyl group attached to each silicon (IV). For lack of a simple systematic name, the designation “octamethyl Ts” is used for this molecule. It is quite likely t h a t Scott’s’4 subliiiiahle crackiiig product was, in fact, “octamttliyl rTs.” Barry antl (:ilke?rln suggested similar structure>for their cyclic hydrolysis products. ‘ ~ I J ~lower T tiielting subliinable solid was recognized as n polpnier hoiiiolog. It could differ froiii “ineth>-lTs” by any multiple of the unit C2H&O:{. That is, i t could be “methyl Ts,”‘‘Ti{,,’’ “Tn’ etc., litit not “illethyl T4,” which is presumably sterically impossible. The deterininecl molecular weight is very close to that calculnted for “hexarnethvl Tc,” T‘. Re-examination of several distillatcs obtained from partial hydrolysis products of tnethyltriethoxysilane disclosed that very small amounts of “inethyl ?‘R’l frequently- were preseiit in solution. esIpccially i l l thc lower boiling fractions. n!,
Aug. 5, 1955
PARTIAL HYDROLYSIS OF METHYLTRIETHOXYSILANE
3993
appropriate treatment i t again was possible to isolate small amounts of this completely condensed. cyclic product.
Fig. 1.-Photograph of "octarnethyl Ts," constructed from Fisher-Hirschfelder models.
Figure 1is a photograph of a Fisher-Hirschfelder model of "octamethyl T8," in which the highly symmetrical, cage-like character of this molecule is illustrated. A model of "hexamethyl Ts" cannot be constructed satisfactorily. Figure 2 is a view of the nearly completed model, showing the spatial relation of the 6- and 8-membered rings and the resulting dissymmetry. Figure 2a ihows the extent to which the model fails to allow closure of
i( i
b
Experimental Hydrolysis of Methyltriethoxysilane in Benzene with Three Molar Equivalents of Water.--One mole (178.4 g.) of methyltriethaxysilane (Dow-Corning Corp., 99% purity, b.p. 143.5'), dissolved in 500 ml. of C.P.benzene, was stirred rapidly, and the mixture heated to boiling (81 ")under a reflux condenser. Three moles (54.0 9.) of water containing 0.2 ml. of 35.4% HCI was added in 15 minutes. The temperature dropped to 68.0'; then, as heating and stirring were continued, the equilibrium liquid temperature dropped to 64.6" in one hour. A modified Dean-Stark trap was attached, and 33 ml. of aqueous distillate was removed in one hour a t 64.7-65.5". This contained some ethanol and benzene and some of the HCl, in addition to water. The solvents then were distilled (500 g., b.p. to 81", d. 0.85, 1.4640, containing approximately 134 of ethanol and an additional 11 ml. of aqueous distillate?: The residue (106.5 9 . ) was filtered t o remove suspended gel (1.0 g.), and subjected to vacuum distillation. After residual solvents were removed, 10.2 g. of oil boiling a t 130-
Fig. 2.-a: photograph of model of "hexamethyl Te," showing 6 and amembered polysiloxane rings. b: reverse side of "hexamethyl T." showing failure of model to allow complete ring closure.
140' at 3 mm. came over. The remainder (60.5 9.) then rapidly gelled. The final pot temperature was 200". A run with double the quantities of reagents yielded only 6.3 g. of oil, and resulted in 128.5 g. of gelled resin. Table I summanes the data obtained in a number of similar mns. A d . Calcd. for c,&i&iich,: C, 24.4; H , 6.1; Si, 34.0; OH, 6.9; OGH6, 18.2; mol. wt., 495.7. Calcd. for CtoH~sSisOlo:C, 25.3; H , 5.9; Si, 35.4; OH, 0.0; O W S , 18.9; mol. wt., 477.7. Found (oils from runs 1, 2, and 5): C, 25.9, 25.5, 25.0; H, 6.0, 5.9, 6.5; Si, 34.3, 33.2, 33.9, 35.7; OH, 2.5, 2.4; OGH,, 17.6, 17.0; mol. wt., 478, 525. Calcd. far (C,6H48Si120m),: C, 21.4; H, 5.4; Si, 37.5; OCsHr, 10.0. Found (gel from run 2): C, 20.9; H , 5.6; Si, 37.6; OGH,, 9.0.
TABLE
I
HYDROLYSIS O F ~ ~ E T I I Y L T R I E T H O X Y S I L A UIEN BENZEYE II'ITH THREE h I ( I L ~ 5O f
I:lln
1 2 3 4 5h
6"
.
moles
Benzene ml.
n't ,
0.5 1.0 2.0 1.0 1.0 1.0 0.5
500 500 1000 1000 1000 1000 500
2.0 10.2 6.3 11.5 7.0 5.2 0.6
MTS,~
r.
9 ~Icthyltriethoxysil~nc. A-0 catalyst used.
I'rnction
oc.
8 , 9,1:I
8;. 5
21 31,82 44 49,50 58
91.5 110.5 99 120 138
.,, . O b s d . b.p.
ic. 7 3 3- 1.X 130-140 120-130 135-143 125-133
\vATFR
-__
Products----
srm.
Gel, 112"D
15 ... 11.2 3 1.410s 1.0 1 1 ,4223 1 .0 1 1.4168 25.0 1 1,4208 30.0 13il--1:13 3 1,4183 30.0 1~)ILlE 0.4 ... 11.3 Distillation through the Deati-Stark trap omitted.
_.__.___. .\,,al)sr 5,;. 9
128.5 32 6 30.0 :34.0 14.0
