- Email: [email protected]
Heats of formation of silicon tetrachloride, dimethyldichlorosilane and diphenyldichlorosilane
JOVRXU,
Iq
HEATS
OF
FORJSATIOS
DICHLOROSILXXE
31:X.
RIXG.
Dcpadmcnr (Received
H. E. O’SEXL. rSth.
SILICOS
TETRACHLORIDE,
CHE31ISTRY
DIJIETHTL-
_K.ZiD DIPHEXYLDICHLOROSILXXE
of Cfmnis:r3. 3fay
OF
OF ORC.ISOJ~ET_GI,XC
_a_ He KADHI-U
San Diego
.~SD FRED
JXPPE
Stale Cdicgc. _%nz Diego, Cuifp71ia
g-‘xrS (G.S._-z .)
rg6~)
E.TRODC‘CTIOS
Heats of formation of the majorit_v of organosilicon cornpour& are unknown. The orgzxm&IorosiIanes may be included in this cate,ooF_ Ex-en the heat of formation of silicon tetrachloride is not well resoh-ed. Since estensive combustion studies have been made on the polydimeth_vI and the pol~diphenyIsiIosanes, which are the condensed hydro!yGs products of dimethyl and diphenyklichlorosilane, the heats of formakion of the corresponding chIorosiIanes ma>- be determined from additional data OR their heats of hydroIysis_ in this paper we describe the determination of the heats of h>-drolysis of sex-eraI chiorojilanes and discuss the enthaIpy bond additivit>- re-lationships in these compounds. ESPERI3lESTAL
The cornpour& studied were ub~tained from the Marhewn, Cole-man. and Bell Compan_v_ Each compound was \-acuum distilled to remove dissolved hydrogen chIoride_ H>-drolyzed samp!os of each compound were anafvzed for chIoride ion. and the foliowiq sample purities were obtained: Siiicon tetrackoride (~9.9 5 0.0s Og), dlmethyidichlorosiIane (gi_Go 2 0-15 :; j. trimethyIchIorosiIane ($.oS + 0.03 y&j, phr;lyItrichlorosikne (99-70 + 0.06 ?A) and diphen~!dichIorosiIane (c)$51 & 0.0-3 sOj_ The analyes showed that the hydroIysis reactio:ls did go to completion. Proton oucfear mqnetic resonance spectra were obtained for dimeth>-I and diphen- dichlorosilane. trim&h>-Ichiorociiane and pheny-lrrichloroziiane. The spectra showed that the Dimethyldichlorosikme and trisampies were free from reciprocaI contamination. methvlchtorosiiane were treated with Iithium aiuminum hydride in di-n-but_\-1 ether. So si&ne was formed indicating that silicon tetrach!oridi, a possibIe contaminant, 1k-x not present. The calorimeter used was similar in design and operation Stem and Passchierx_
to one described by
The heats of hyiroI_vsis are iisted in Table I. Corrections for sample purity were made on the assumption that the impurity did not h)-drolyze.
162.05 167.S*
79-35
=--1x x.zrg
Ii3.10
79.33 so.os
I.ISO
X7+.36
I-339 a.S2+
X71-$
r.Qoj
3r.23
I_*=$
166.30 159.96
1.r3S I .046
I7.+3S Ii+.67
3=-73 31.66
I.267
I=&72
55-1-O
0.962
159-77 rg.S.67
55-15 5+-1-3
X.0=$
J.54-93 zyj.js
55.4 f3_22
LA&
159.36
s-19
131;
2$5.0s
;=.I2
2.035
“25_S3
3’_06
1.036
-‘3”_30
12.70
x-099 12S3
70.99 I%.?9
11.9.l X3.00
I-t57
r.399
(C,H,),SiCi,
C,H,Sict,
16S.6S
175.61
O-933 I-991
(CH,),SiCI, (CHJ,SiC1
=
-79-75
& 0.14
;g.ss
79.73 so.03 33-0-t 30-55
I_IS~
I_iS.OO
12.21
X.085
I;$;2
I~.00
I.350
r6S.94
IX-77
r.Ag’
164.52
Ij.XO
I_163
I7J_3S
I'.00
-p-09
-_1 0.03
--Iz&?
&
0.19
The heats oi formation of gaseous silicon tetrachIoride, dimeth7;IdicMorosilane and diphen>-1dichloroGlane [Table 3) were obtained from the appropriate combinations of the folloxing reactions: SiCl,tg)
i;iCt,(l)
fH’r’
+ 2
f
SiCt,jZ)
fr)
Hz0 _Si6,
ICH2),SiC!,&]
AHig’ s
~C&j2SiCt,(i)
+ 2 H,O
(CottoidaIsofn.] + &rffCt-goo H,O)
(4
(CH.J,SiCL(Z) *+
(3)
(CH,),Si(OH)2(aq) + z{HCI-5~
Z,o)
.
(C$i&SiCl,tp) ‘%” + (C&&SK%(Z) ~r;,H,).+ricl,;ij+ I?Hz0 -fHoi
(C&iJ+(OH),(aq)
I-r) (51
+ z(HC1-500 H,O) J_ Or~anomrfal.
Chem..
(6) 5 (x966)
rzq-SzQ
126
31. A_ RISG,
TABLE
11. E_ O’SEAL,
A_ H.
ILlDNIu,
F. J_*PPE
2
SiCI, CH,SiCJ, CzH,SiCI, C,H,SKJ,
-153-7 -r56_9
I-
--;O.I
-163.4
‘8
-_51_5
-_52_1 -55. I -4i.6 -3z5 -32.1 -31-6 -x6.x
(CH&SiCL _ (C,H5),SiCJ, (CH&SiCl
-12.4
b
s
a
8
b
a
b
s
-1os.o -1os.4 - jl.3
b b
paper.
b SC cornbu&on
s c ii a ---
a This
a
--;g.s -76.6
da& ;rraihb!c.
The &a[ products of the h>-drolysis reactions are written as silanols which are krmx-n to polymerize. Howe\-er, the polymerizations o f silanok are reactions in which s:{Si-OM) and +iO-H) bonds are broken and rr(H-OH] and x(SiO-53) bonds are forme& \1-ri~ren in ferms of the bonds;, the poIymerization reactions xe di+ proporti~onations wd therefore. assuming that ‘bond additivity rcfationships holctc, should have Zero enthalpies. Therefore, the actual final product should not effect :he heat of formation calculations_ tie other fact can ako be considered. The hydrolysis reactions are v-er~-rapid while soi~e polymerization reacrions are not_ The rare of po!ymcrization of silanols decrease with increasing aerhyi stibstitution and great&- decreases \sith increasing phenyi s>lbstitution7_ XIso, each successix-e condensation product is more stabk than its precurs&. Therefore, at Iea~t for diphen>-Isilanediol, little pal_\-merization shouId occur during our heat of hydrolysis measurements. The variations apparent in Table 2 for the heats of E~drol~-Gs of the chIor&lanes studied are much larger than one would expect for such elementary reaction c&ximete tti,-hniques. The most probable source of these errors is sampIe pm-it!-, since these compounds are not readif_\-obtainabk in a high degree of putit>-. -3s described in the espetimental section. we carefulI>- examined our sarrples for cross-contamination
HE_%TS OF FORMATIOS
OF CIILOROSIL_~SES
I27
and chloride content. Similar precautions, if any, exercised by other workers have not been described. It is our opinion that chloride analysis alone is not a sufficient indication of sample purit\-. It should also be noted that the most probable errors in sample purity would lead to less esothermic heats of hylrolysis for silicon tetrachloride and phenyltrichlorosilanes and a more esothermic heat of hydrolysis for trimeth_vlchlorosilane. The data suggest that the heats of hydrolysis for chlorosilanes containing the same number of silicon4loride bonds are rather insensitive to the nature of the organic group bonded to silicon. In addition, all data shorn a consistent decrease in the hydroI>-sis heat per silicon-chloride bond in going from the tetracfiloride to the monoch!oride_ _-Although the heats of hydrolysis may he interpreted in terms of many separate heat terms such as heats of solution or heats of vaporization, such a variation in the hydroIysis heats couId be interpreted as an indication of silicon-chloride bond strengthening with increasing degree of chlorine s-ubstitution. Examination of Table 3 shows that prior to the hydrolysis studies reported here, four separate determinations of the heat of formation of silicon tetrachloride had been made using three d&rent standard reactions_ The results of these earlier studies5-11
centered on the two values of llH”,- = -136.9 and -163.3 kcal/mole. Our hydrolysis result supports the more positi\-e \-ahre. It should be mentioned that in all of these dett_rminations, the mosr probable espcrimental errors (sample purity and loss of sample b>- evaporation during the reaction) would lead to more negative heats of formation of silicon tetrachloride. Thus, we feel that a dHO~~SiC1,~)~ = -133-S hcal~mole obtained as the a\-erage of the three more positive results represents a “best \-alue” at this time. It is interesting to examine the enthalpy bond additivity relations in the chlorosilanes as a function of the degree of chlorination. Silicon-methyl (Si-Me) and silicon-phenyl (Si-Ph) enthalp>- bond additivities are --r&o and +IO.~ kcal/molebond respcctivelv5. \\‘ith these values and the determined heats of formation of dimethyldichlorosilane and diphen-ldichlorosilre we obtain Si-Cl bond additkities of -36.:: and -36.6 kcal:mole-bond in these disubstituted chlorosilanes. The Si-Cl bond additivitv in silicon tetrachloride using dH”fSiCl,(.y)l = -153.S kcal/mole is -354.9 hcal:lmole-bond. An examination of the heats of formation of man- meth+contaimng or.zanosiIicon compounds has previously shown no lariation of the silicon-methyl bond strength with degree of methyl substitutiox9. Thus, there appears to be a defmite
163
31. A. RISG,
H. E. O’SE.=iL,
_a_ H. KADHI~CI, F_ JAPPE
bond strengthening of the order of 2 kcaljmole-bond per S&Cl bond with an increase in chlorine sub>%tution in the chlorosilanes. If our zero enthalpy assumptions for the condensation reactions of the silanols are incorrect and the enthalpks of the reactions are negative, the heats of formation of the organochIorosiIaes would be more positive than we calculate. Therefore, e\-en if our zero enthalp- assumptions are incorrect, the conclusion of silicon-chlorine bond strengthening \vith an increase in chlorine substitution is still valid. This apparent change in the silicon-chlorine bond strength which suggests that bond add&iv&~- relationships do not hoid in the organochlorosilanes appears to cast doubt on the x-aWit_\-of our zero enthalp>- assumption for the silanol condensations_ sowe\-er. during the condensation reactions, the siiicon atoms are always bonded to the same number and kind of atoms and therefore the bond additivity relationships should LoId veq- well for the siiicon compounds invok-ed. \Fith the formation of water an O-Si bond is broken md ark O-H bond is formed_ Since the electronegativity of hydrogen and silicon are not too different, bond additivit- relationships should ako be valid for this part of the reaction q-stem. The observed bond strengthening can be rationalized on the basis of an increase in “s’* character in the hybridized silicon orbit& bonded to chIorine with incre&ng degree of chlorination”. The obser\-ed decrease in silicon-halogen bond length with an &creasing degree of halogenation in the haIo-siianes support this h>-pothesiP_ Thm, the bond Icngth and bond add&x-it- x-ariations would be expected to occur when the electronegativity of the Ii,oands are appreciabI>- different from each other. It would be of interest to obtain and trichforosilanes and for compounds
accurate heats of formations for some monoof the other halosiiane series.
The authors are indebted fo the L--S_ Army- Research ofice (Durham) and the SatiLtnal Scicncr--Foundation for fin=&1 ajsi~ance.
Heats of h_\drol-sis in aqueous solutions have been obtained for the following chtorosilanes: SiCI, i-79-75 = 0.14 kcaI~‘nwIr). (CBH5j2SiC12 1--31-64 +- 0.46 kcaI/ moIe>. C,K5SiC13 (---3~_07 & o-17 kcai_‘mole),
(CH,jLSiCI,
(-3zog
ti 0.03 kcal,‘moIej
kczl,‘moIe,!. From these data we have calculated heats of formarion for the foiiowing .gzjcous chfnrosilanes: SiCI, (-153-7 kcaljmolej. (CH,‘) SiCf, (--10s.~ kcal~molcj and (C,H,j SKI, ( --~z.z !xalz.moIej _ _-I change in silicon-chlorine bond strength with degree of chIorination is disand
(CH,!,SiCI
Cl.lZf?d.
(--IZ_~
2
0.19
IZE_ATS OF FORLTIOS 6 ; 8 Q IO IX 12 13
OF C_rLLOROSLL_~SES
129
S. U-. Bassos ASD J_ IL Buss. -1. Ckrz. F’itys., “g (195s) 5+6. C. EABORS. Or~at:osiiicott Corttpozotd~, Academic Press, Xew York. Ig6o. p- z+-‘?~o. K. _A_ _%SDRI_XSOX’ ASD S. A. Px~~Lo~-, DokZ. Akad. Sauk SSSR. SS (1953) SXI. \\‘. A. ROTH AXD 0. SCXWARTZ. 2. Phys. Ckent.. 134 (192s) 456. H_ SCHAEFER _&SD H. HEISE. 2. -4t:org. _-li@tt. Chent., 331 (1964) 25. _a_ E. BEEZER MD C. T. MORTIUER, J. Cicent. SOL, (1964) z7’7H. A. BEST. /_ Cbctx. Edtrc.. 3; (x960) 616: also. Ckrrn. Rcr.. 61 (xg6r) 275. E. A. \-_ ESSX\~ORTH.I’o!attk Silt&t Cotttpouttds. MacMilIan. Sew York. 1963, p. 56. J_ or,attotnrfaZ.
Cheat..
5 (rg66)
xq-I”g
Iq
HEATS
OF
FORJSATIOS
DICHLOROSILXXE
31:X.
RIXG.
Dcpadmcnr (Received
H. E. O’SEXL. rSth.
SILICOS
TETRACHLORIDE,
CHE31ISTRY
DIJIETHTL-
_K.ZiD DIPHEXYLDICHLOROSILXXE
of Cfmnis:r3. 3fay
OF
OF ORC.ISOJ~ET_GI,XC
_a_ He KADHI-U
San Diego
.~SD FRED
JXPPE
Stale Cdicgc. _%nz Diego, Cuifp71ia
g-‘xrS (G.S._-z .)
rg6~)
E.TRODC‘CTIOS
Heats of formation of the majorit_v of organosilicon cornpour& are unknown. The orgzxm&IorosiIanes may be included in this cate,ooF_ Ex-en the heat of formation of silicon tetrachloride is not well resoh-ed. Since estensive combustion studies have been made on the polydimeth_vI and the pol~diphenyIsiIosanes, which are the condensed hydro!yGs products of dimethyl and diphenyklichlorosilane, the heats of formakion of the corresponding chIorosiIanes ma>- be determined from additional data OR their heats of hydroIysis_ in this paper we describe the determination of the heats of h>-drolysis of sex-eraI chiorojilanes and discuss the enthaIpy bond additivit>- re-lationships in these compounds. ESPERI3lESTAL
The cornpour& studied were ub~tained from the Marhewn, Cole-man. and Bell Compan_v_ Each compound was \-acuum distilled to remove dissolved hydrogen chIoride_ H>-drolyzed samp!os of each compound were anafvzed for chIoride ion. and the foliowiq sample purities were obtained: Siiicon tetrackoride (~9.9 5 0.0s Og), dlmethyidichlorosiIane (gi_Go 2 0-15 :; j. trimethyIchIorosiIane ($.oS + 0.03 y&j, phr;lyItrichlorosikne (99-70 + 0.06 ?A) and diphen~!dichIorosiIane (c)$51 & 0.0-3 sOj_ The analyes showed that the hydroIysis reactio:ls did go to completion. Proton oucfear mqnetic resonance spectra were obtained for dimeth>-I and diphen- dichlorosilane. trim&h>-Ichiorociiane and pheny-lrrichloroziiane. The spectra showed that the Dimethyldichlorosikme and trisampies were free from reciprocaI contamination. methvlchtorosiiane were treated with Iithium aiuminum hydride in di-n-but_\-1 ether. So si&ne was formed indicating that silicon tetrach!oridi, a possibIe contaminant, 1k-x not present. The calorimeter used was similar in design and operation Stem and Passchierx_
to one described by
The heats of hyiroI_vsis are iisted in Table I. Corrections for sample purity were made on the assumption that the impurity did not h)-drolyze.
162.05 167.S*
79-35
=--1x x.zrg
Ii3.10
79.33 so.os
I.ISO
X7+.36
I-339 a.S2+
X71-$
r.Qoj
3r.23
I_*=$
166.30 159.96
1.r3S I .046
I7.+3S Ii+.67
3=-73 31.66
I.267
I=&72
55-1-O
0.962
159-77 rg.S.67
55-15 5+-1-3
X.0=$
J.54-93 zyj.js
55.4 f3_22
LA&
159.36
s-19
131;
2$5.0s
;=.I2
2.035
“25_S3
3’_06
1.036
-‘3”_30
12.70
x-099 12S3
70.99 I%.?9
11.9.l X3.00
I-t57
r.399
(C,H,),SiCi,
C,H,Sict,
16S.6S
175.61
O-933 I-991
(CH,),SiCI, (CHJ,SiC1
=
-79-75
& 0.14
;g.ss
79.73 so.03 33-0-t 30-55
I_IS~
I_iS.OO
12.21
X.085
I;$;2
I~.00
I.350
r6S.94
IX-77
r.Ag’
164.52
Ij.XO
I_163
I7J_3S
I'.00
-p-09
-_1 0.03
--Iz&?
&
0.19
The heats oi formation of gaseous silicon tetrachIoride, dimeth7;IdicMorosilane and diphen>-1dichloroGlane [Table 3) were obtained from the appropriate combinations of the folloxing reactions: SiCl,tg)
i;iCt,(l)
fH’r’
+ 2
f
SiCt,jZ)
fr)
Hz0 _Si6,
ICH2),SiC!,&]
AHig’ s
~C&j2SiCt,(i)
+ 2 H,O
(CottoidaIsofn.] + &rffCt-goo H,O)
(4
(CH.J,SiCL(Z) *+
(3)
(CH,),Si(OH)2(aq) + z{HCI-5~
Z,o)
.
(C$i&SiCl,tp) ‘%” + (C&&SK%(Z) ~r;,H,).+ricl,;ij+ I?Hz0 -fHoi
(C&iJ+(OH),(aq)
I-r) (51
+ z(HC1-500 H,O) J_ Or~anomrfal.
Chem..
(6) 5 (x966)
rzq-SzQ
126
31. A_ RISG,
TABLE
11. E_ O’SEAL,
A_ H.
ILlDNIu,
F. J_*PPE
2
SiCI, CH,SiCJ, CzH,SiCI, C,H,SKJ,
-153-7 -r56_9
I-
--;O.I
-163.4
‘8
-_51_5
-_52_1 -55. I -4i.6 -3z5 -32.1 -31-6 -x6.x
(CH&SiCL _ (C,H5),SiCJ, (CH&SiCl
-12.4
b
s
a
8
b
a
b
s
-1os.o -1os.4 - jl.3
b b
paper.
b SC cornbu&on
s c ii a ---
a This
a
--;g.s -76.6
da& ;rraihb!c.
The &a[ products of the h>-drolysis reactions are written as silanols which are krmx-n to polymerize. Howe\-er, the polymerizations o f silanok are reactions in which s:{Si-OM) and +iO-H) bonds are broken and rr(H-OH] and x(SiO-53) bonds are forme& \1-ri~ren in ferms of the bonds;, the poIymerization reactions xe di+ proporti~onations wd therefore. assuming that ‘bond additivity rcfationships holctc, should have Zero enthalpies. Therefore, the actual final product should not effect :he heat of formation calculations_ tie other fact can ako be considered. The hydrolysis reactions are v-er~-rapid while soi~e polymerization reacrions are not_ The rare of po!ymcrization of silanols decrease with increasing aerhyi stibstitution and great&- decreases \sith increasing phenyi s>lbstitution7_ XIso, each successix-e condensation product is more stabk than its precurs&. Therefore, at Iea~t for diphen>-Isilanediol, little pal_\-merization shouId occur during our heat of hydrolysis measurements. The variations apparent in Table 2 for the heats of E~drol~-Gs of the chIor&lanes studied are much larger than one would expect for such elementary reaction c&ximete tti,-hniques. The most probable source of these errors is sampIe pm-it!-, since these compounds are not readif_\-obtainabk in a high degree of putit>-. -3s described in the espetimental section. we carefulI>- examined our sarrples for cross-contamination
HE_%TS OF FORMATIOS
OF CIILOROSIL_~SES
I27
and chloride content. Similar precautions, if any, exercised by other workers have not been described. It is our opinion that chloride analysis alone is not a sufficient indication of sample purit\-. It should also be noted that the most probable errors in sample purity would lead to less esothermic heats of hylrolysis for silicon tetrachloride and phenyltrichlorosilanes and a more esothermic heat of hydrolysis for trimeth_vlchlorosilane. The data suggest that the heats of hydrolysis for chlorosilanes containing the same number of silicon4loride bonds are rather insensitive to the nature of the organic group bonded to silicon. In addition, all data shorn a consistent decrease in the hydroI>-sis heat per silicon-chloride bond in going from the tetracfiloride to the monoch!oride_ _-Although the heats of hydrolysis may he interpreted in terms of many separate heat terms such as heats of solution or heats of vaporization, such a variation in the hydroIysis heats couId be interpreted as an indication of silicon-chloride bond strengthening with increasing degree of chlorine s-ubstitution. Examination of Table 3 shows that prior to the hydrolysis studies reported here, four separate determinations of the heat of formation of silicon tetrachloride had been made using three d&rent standard reactions_ The results of these earlier studies5-11
centered on the two values of llH”,- = -136.9 and -163.3 kcal/mole. Our hydrolysis result supports the more positi\-e \-ahre. It should be mentioned that in all of these dett_rminations, the mosr probable espcrimental errors (sample purity and loss of sample b>- evaporation during the reaction) would lead to more negative heats of formation of silicon tetrachloride. Thus, we feel that a dHO~~SiC1,~)~ = -133-S hcal~mole obtained as the a\-erage of the three more positive results represents a “best \-alue” at this time. It is interesting to examine the enthalpy bond additivity relations in the chlorosilanes as a function of the degree of chlorination. Silicon-methyl (Si-Me) and silicon-phenyl (Si-Ph) enthalp>- bond additivities are --r&o and +IO.~ kcal/molebond respcctivelv5. \\‘ith these values and the determined heats of formation of dimethyldichlorosilane and diphen-ldichlorosilre we obtain Si-Cl bond additkities of -36.:: and -36.6 kcal:mole-bond in these disubstituted chlorosilanes. The Si-Cl bond additivitv in silicon tetrachloride using dH”fSiCl,(.y)l = -153.S kcal/mole is -354.9 hcal:lmole-bond. An examination of the heats of formation of man- meth+contaimng or.zanosiIicon compounds has previously shown no lariation of the silicon-methyl bond strength with degree of methyl substitutiox9. Thus, there appears to be a defmite
163
31. A. RISG,
H. E. O’SE.=iL,
_a_ H. KADHI~CI, F_ JAPPE
bond strengthening of the order of 2 kcaljmole-bond per S&Cl bond with an increase in chlorine sub>%tution in the chlorosilanes. If our zero enthalpy assumptions for the condensation reactions of the silanols are incorrect and the enthalpks of the reactions are negative, the heats of formation of the organochIorosiIaes would be more positive than we calculate. Therefore, e\-en if our zero enthalp- assumptions are incorrect, the conclusion of silicon-chlorine bond strengthening \vith an increase in chlorine substitution is still valid. This apparent change in the silicon-chlorine bond strength which suggests that bond add&iv&~- relationships do not hoid in the organochlorosilanes appears to cast doubt on the x-aWit_\-of our zero enthalp>- assumption for the silanol condensations_ sowe\-er. during the condensation reactions, the siiicon atoms are always bonded to the same number and kind of atoms and therefore the bond additivity relationships should LoId veq- well for the siiicon compounds invok-ed. \Fith the formation of water an O-Si bond is broken md ark O-H bond is formed_ Since the electronegativity of hydrogen and silicon are not too different, bond additivit- relationships should ako be valid for this part of the reaction q-stem. The observed bond strengthening can be rationalized on the basis of an increase in “s’* character in the hybridized silicon orbit& bonded to chIorine with incre&ng degree of chlorination”. The obser\-ed decrease in silicon-halogen bond length with an &creasing degree of halogenation in the haIo-siianes support this h>-pothesiP_ Thm, the bond Icngth and bond add&x-it- x-ariations would be expected to occur when the electronegativity of the Ii,oands are appreciabI>- different from each other. It would be of interest to obtain and trichforosilanes and for compounds
accurate heats of formations for some monoof the other halosiiane series.
The authors are indebted fo the L--S_ Army- Research ofice (Durham) and the SatiLtnal Scicncr--Foundation for fin=&1 ajsi~ance.
Heats of h_\drol-sis in aqueous solutions have been obtained for the following chtorosilanes: SiCI, i-79-75 = 0.14 kcaI~‘nwIr). (CBH5j2SiC12 1--31-64 +- 0.46 kcaI/ moIe>. C,K5SiC13 (---3~_07 & o-17 kcai_‘mole),
(CH,jLSiCI,
(-3zog
ti 0.03 kcal,‘moIej
kczl,‘moIe,!. From these data we have calculated heats of formarion for the foiiowing .gzjcous chfnrosilanes: SiCI, (-153-7 kcaljmolej. (CH,‘) SiCf, (--10s.~ kcal~molcj and (C,H,j SKI, ( --~z.z !xalz.moIej _ _-I change in silicon-chlorine bond strength with degree of chIorination is disand
(CH,!,SiCI
Cl.lZf?d.
(--IZ_~
2
0.19
IZE_ATS OF FORLTIOS 6 ; 8 Q IO IX 12 13
OF C_rLLOROSLL_~SES
129
S. U-. Bassos ASD J_ IL Buss. -1. Ckrz. F’itys., “g (195s) 5+6. C. EABORS. Or~at:osiiicott Corttpozotd~, Academic Press, Xew York. Ig6o. p- z+-‘?~o. K. _A_ _%SDRI_XSOX’ ASD S. A. Px~~Lo~-, DokZ. Akad. Sauk SSSR. SS (1953) SXI. \\‘. A. ROTH AXD 0. SCXWARTZ. 2. Phys. Ckent.. 134 (192s) 456. H_ SCHAEFER _&SD H. HEISE. 2. -4t:org. _-li@tt. Chent., 331 (1964) 25. _a_ E. BEEZER MD C. T. MORTIUER, J. Cicent. SOL, (1964) z7’7H. A. BEST. /_ Cbctx. Edtrc.. 3; (x960) 616: also. Ckrrn. Rcr.. 61 (xg6r) 275. E. A. \-_ ESSX\~ORTH.I’o!attk Silt&t Cotttpouttds. MacMilIan. Sew York. 1963, p. 56. J_ or,attotnrfaZ.
Cheat..
5 (rg66)
xq-I”g