1198
NOTES
Vol. 66
phase in the water-rich region of the system is, within experimental error, pure ice and not the solid solution claimed by Ballb. Aside from mme obvious mistakes in the phase diagrams shown by him,it is believed that the results obtained by Ball6 are incorrect because of misapplication of the method of tracers, misinterpretation of the data, and poiasible errors made by him in the chemical analysis of the barium acetate tracer.
ti110
TABLE I WET RESIDUESDATAFOR THE SYSTEMCH3COOSaCHaCOOH-HI0 Wt. %
Tieline no.
1 2 Fig. 2.--\Tlater-rich region of the sgsttin CH8COONaCH3COOH-H20 a t -10.2
.
3
4
5 6
CHaWt. % COON& CHaCOOH
Liquid Residue Liquid Residue Liquid Residue Liquid Residue Liquid Residue Liquid Residue
Mathematically extrapolated terminus
-10.2 f 0.1" 8.98 13.97 0.57 wt. 5.73 9.12 4.49 21.99 .29 wt. 3.51 16.90 12.61 6.83 .34 wt. 9.29 5.12 -13.9 f 0.2" 5.58 27.06 .55 wt. 4.06 18.90 13.10 13.57 .20 wt. 8.87 9.12 .1i wt. 17.11 6.57 11.04 4.31
% CHaCOOH % CH3C001\;a
70 CHSCOOH % CH3COOKa % CHaCOO?;a % CH$OOH
Acknowledgment.-The author wishes to express his sincere appreciation to Profs. John E. Trance and Seymour Z. Lewin of New York University for the generous use of their facilities. The financial support of the National Science Foundation is gratefully acknowledged.
Fig. 3.-Water-rich region of the system CH3COONaCHaCOOH-HzO at - 13.9". salt to the free acid, and total acetic acid was titrated as described above. The sodium acetate then was estimated by the difference. The method was found t o be dependable even in the presence of excess acetic acid. A standard sodium acetate-acetic acid solution was prepared by mixing measured amounts of standardized sodium hydroxide and acetic acid solutions. The results obtained by chemical analysis agreed within 4 parts per thousand of the value predicted on the basis of the concentrations and amounts of the mixed starting materials. I n a different experiment, two separate aliquots of a given solution of sodium acetate (excess acetic acid absent, this time) were analyzed by this method and the results agreed n-ithin 5 parts per thousand of each other. The relative mean deviation for the sodium acetate determination therefore is estimated to be 2.5 parts per thousand. h calibrated buret was employed for all titrations. Commercial reagent grade chemicals without further purification were used throughout.
Results and Discussion According to Ba116, the composition of the saturated solid solution at - 10.2 and - 13.9' would be approximately 14 and 18 weight % CH3COOH, respectively. The results obtained in the present investigation, given in Table I and Fig. 2 and 3, iiidir.:ite, I ~ U ' C T W ,th:ii thc cwmposition of thc solid
THERMODYNANIC STUDIES OF T H E IODINE COMPLEXES OF s-TRITHIAKE, THIACYCLOHEXANE, AND THIACYCLOPENTANE IN CARBON TETRACHLORIDE SOLUTIOK BY J. D. hfCcULLOUGH .k>D
IRlliEL.4
c. ZIMYERMANN
T h e Department of Chemzstry o f the Unsverszty o f CalefoEolnza at Lo8 Angeles, Los Angeles 24, Calzfornza Recesved December l S 8 1961
The present work is an extension of previously reported studies1-3 on systems of the type D - 1 2 = D Iz,where the donor, D, is an organoselenium compound or an organic sulfide.
+
Experimental Materials.-Thiacyclopentane and thiacyclohexane were from the same samples used in ref. 1 and were supplied bq the American Petroleum Institute Research Project 48A, Bartlesville, Oklahoma. s-Trithiane was kindly supplied by Professor E. E. Campaigne of Indiana University. The recrystallized solid melted a t 220-221'. The iodine and carbon tetrachloride and the experimental procedures were those described in ref. 1 and 2. Method of Calculation.-The method of calculation was (1) J. D. McCullough and D. hiuhey. J . A n . Chem. Soc., 81, 1291 11959). 12) J. D. McCiillorlgh and I. C. Zimmermann, J . Phys. Chem., 64, 1064 (1960). (3) 1 I ) \ I I (7iilloiipli n n d T C Z ~ ~ r ~ i n i ~ i r n iul tni dn. ,, 66, XXS (lQOlJ,
1199
XOTES
June, 1982
TABLE I ABSORBANCE DATA
------
Conon. (moles/l.) X 104 -----at 23.0°[D 1 [I21
4.672 5.860 6.221 3.987 6.867 6.678 5.751 5.056 3.735 4.150 3.061 2.422 2.099
--------16.0°300 mp
29.31 25.02 47.94 38.89 21.39 42.13 60.07 48.46 33.20 18.39 30.41 16.06 22.95
DONOR, D, AND I::IN (a) D = a-Trithiane, C3H&
FOR SOLUTIONS OF
.
-Absorbanoe c -
310 mp
320 mp
300 mp
0.978 0,970
1,085 1,092
0.989 0.990
0.720
0.759
1,090 1.100
1.210 1.237
1,107 1.142
1.695 0.902 .540 .688 .297 .400
1.882 1.000 0.603 * 755 .319 .426
1.721 0.91.4 .552 .687 .291 .382
cc1,
per cm. patha- 2 3 . 0 0 ~ - - - - - . 310 mp 320 mp
I 1
---
,--------36.6°-300 mp
310 mp
320mp
1.559 0.840 0,750
0.788 0.833 1.692 0,913 0.832
0.716 0.760 1.526 0.827 0.763
0.548 0.533 1.100 0,633 0.540 1.039
0.582 0.598 1.191 0.664 0.588 1.129
0.530 0.544 1.088 0.600 0.539 1.034
1.728 1.328
1.896 1.405
1.728 1.294
1.284 0,950 ,510 .316 .409 .198 .263
1.368 1.022 0.538 .333 .422 .199 .261
1.260 0.922 ,482 ,302 .378 ,178 .232
(b) D = Thiacyclohexane, C6HlOS Concn. (molix/l.) X 1 0 4 ------at 29.3'---7 I121 [D I
1.005 1.822 1.164 1.402 4.356 6.524 1.276 3.605
4.459 2.783 7.611 2.820 2.047 3.764 6.611 4.565
Absorbance per om. patha------.-------29.30---300 mp 310 mp 320 mp
--.
7--------------
c
300 mp
0,302 .356 ,580 ,275 .597 1.570 0.540
1.074
13,60---7 310mp
320 mp
0,312 .367 I597 .284 .618 1.613 0.559 1.123
0,260 ,305 .495 .236 .515 1.339 0.463 0.921
0.163 ,183 .305 .152 .315 .840 .300 .552
0.159 .178 .295
.150 .307 .812 .289 .536
[Dl
__----310 mp
[I21
9.26 6.491 2.043 12.90 3.883 1.666 1.850 23.59 2.736 12.74 2.627 1.138 15.83 1.846 0.930 4.80 1.267 0.257 13.04 3.294 1.398 15.06 1.210 0.573 7.26 6.896 1.714 a Absorbance values below -0.2
16.0'--320 mp
1.868 1.480 1.670
-
Absorbance per om. ---p-hat-a__-30.30
+iitt
/lei
fTai
rlirn
___--
320 mp
330 mp
310 mp
1.400 1.124 1.258 0.757 .628 ,178
1.161
1.050 0.812 ,977
0.:797 ,610 ,734 ,410 ,340 ,093 ,525 ,230
0,732
0.899
1.094 1.000 0.608 0.842 .516 0,232 ,135 1.277 ,935 ,770 0,516 ,383 ,335 1.539 1.162 were made in 2,000-cm. cells.
76, 7 X 7 i l O i f l i .
-
310 mp
Results and Discussion Absorbance data for the experimental solutions are given in Table I while the K , values and derived thermodynamic constants for the dissociation at 2.5' are given in Tables I1 and 111,respectively. All of the complexes are clearly of the 1 . 1 type, even when 1, is present in considerable excess. Data on 1,4-dithiane3 and thiacyclob~tane~are included in Table 111for comparison purposes. The increase in the dissociation constants in going from thiacyclohexane to 1,4-dithiane to s-trithiane can be explained in terms of the inductive effect. IF it is assumed that the availability of electrons on t he sulfur atoms is increased by the presence of CH, groups in the molecules, it is reasonable to I
.l i O O ,328
330 mfi
that described in ref. 2 and 3 which involves cyclic leastsquares treatment of the data by means of a modification of the equation proponed by S ~ o t t . ~
( 1 ) 13
0,0950 .lo80 .1795 .OS95 ,1795 .479
0.142 .154 .257 .135 .264 .702 .251 .462
(c) D = Thiacyclopentane, C4H8S Conon. (molss/l.) X 10" _---at 30.30----
7
7-----42.70-.-----. 300 mp
,548 .464 ,122
.694 302
,580 ,719 ,410 ,358 ,090
I500 ,215 ,599
310 mp
320 mp
0.0970 ,1095 .1825 .0905 .1810 .490 .1745 .337
0.0820 ,0925 ,1550 ,0775 .1625 ,415
40 50 32; mp
.1500 .288
_I_____
0.660 ,522 ,649 ,370 ,323
,081 .453 ,195 ,538
330mp
0.498 ,395 .489 ,281 .249 ,061 ,342 ,148
.410
assume further that the effect will tend to be greater when the ratio of CH2 groups to S atoms is greater. Thus the availability of electrons at sulfur should fall off in going from thiacyclohexane to 1,4dithiane to s-lrithiane. The effect that this has on the dissociation constaiits is even more pronounced if one makes statistical allowance for the fact that the number of sulfur reaction sites increases from one to two to three in the series. That the ratio of CHX groups to S atoms is not the whole story is shown by the fad, that the iodine complex of thiacyclopentane is more stable than that of thiacyclohexane. However, the work of Tamres and Searless has shown that the stabilities of the complexes fall off in going to the four-membered ring, C3H6S, and still further in going to the three-membered ring, C2H4S.
1200
Vol. GG
KOTE8
TABLE I1 VALUESOF KOFOR D*12DISSOCIATIOX AT VARIOUS TEMPERATURES AND WAVELEKGTHS ( a ) D = s-Trithiane, CaH&(K, X 10) 15.0'
h(md
c
300 310 320
61,600 70,700 65,800
(11)
D
=
1.011 0.990 0.982 Av. 0.994
36.6'
1.36 1.33 1.32 1.34
1 77 1.77 1.75 1.23
Thiacyclohexane, Cb1&S ( K c X 108)
h(nw)
€
300 310 320
30,900 32,200 26,900
(c)
23.0'
13.6'
4.43 4.40 4.39 Av. 4.41
29.3'
42.7'
8.19 8.34 7.70 8.08
13.7 13.8 13.4 13.6
D = Thiacyclopentane, CAH8S( K c X 108)
X(md
e
310 320 330
13,300 15,100 13,600
16.0'
3.28 3.34 3.35 Av. 3.32
30.3'
40.5'
6.40 6.51 6.44 6.45
11.2 11.3 11.3 11.3
TABLE I11 DISSOCIATION O F D.12 COMPLEXES IN CARBON TETRACHLORIDE SOLUTION AT 25' CONSTANTS FOR
'rHERMODYNAhlIC
Donor (D) s-Trithiane 1.4-Dithiane Thiacyclohexane Thiacyolopentane Thiaeyelobutane
Kc,
AS@ oa1Jdei.l mole 11 7 f 1 4
moles/l. 1 48 X 10-1
AFcO, AH@. kcal./mole kcal./mole 1 14 f 0 04 4 6 f 0 4
1 30 X 7 40 X 10-8 8 56 X 10-a*
2 59 f 2 92 & 2 83
03 6 2 f 03 7 1 f
3 2 2 2
03 8 7 f 4 8 7 i1 4 7 03 f .17 14 9 f 0 6 6 57 f 08 13 4-1;O 3
5.60 1 30 1 29 I 15
X X X X
10-8 10-6
10-zd 10-ae
10 f 59 58 66
3 3
12 1 f 1 0 14 1 f 1 0
a Ref. 3. Ref. 1, data recalculated by method of present work. Ref. 5, X = 436 mp. Ref. 5, X = 310 mp. a Ref. 1.
Acknowledgments.-The authors wish to express their thanks to the National Science Foundation for financial assistance under Research Grant KSFG12884 and to the Numerical Analysis Research Project of the UCLA Department of Mathematics and the Western Data Processing Center for access to the IBM 7090. We also wish to thank Professor Tamrcs of the University of Michigan and Professor Searles of Kansas State University for their cooperation, especially in keeping us informed regarding their own progress and results prior to publication.
THE HEAT OF FORMATIOK OF D IFLUOROSILYLESE BY JOI-INL. M A R G R ~ VADLI E , 8. KAKAAY, Department 01 Ctremtstfy, r/ntueTmly 01 Wz&uInazn. Nadarorr, ~a8Corkarn AND
DOYALD C. PEASE
E . I. du Punt de A'emours and Company, Walmington, Dehuare Recewed December 1 4 , 1961
Difluorosilylene (SiFJ has been prepared ill good yield by passing silicon tetrafluoride over silicon, silicon carbide, silicoii metal alloy, or binary
silicides of polyvalent metals.' SiFz radicals are also important species in the decomposition of silicon tetrafluoride, along mjth SiF and SiFs, and should be useful in the preparation of new compounds containing silicon and fluorine. It is essential that SiFz be prepared under carefully controlled conditions of temperature, pressure, and quenching. Peasel reported a temperature in the range of 1100-1400°, an absolute pressure of not more than about 50 mm., and a quenching of the products to a temperature lower than about 0' within a period of 0.1 to 0.001 sec. as the preferable conditions for a successful reaction. While the product of the SiF, Si (or silicide) reaction is essentially SiF, (monomer or polymer), the purity of the difluorosilylene is lowered by the presence of small amounts of silicon monofluoride, SiF, or silicon trifluoride, SiFB. The emission spectrum of SiF has been examined by various workers. Johns and Barrow2 reported band systems in the Schumaiin region and in the infrared region as far out as 9000 A. They estimate the ionization potential for SiF to be 7.3 e.v. and the heat of dissociation, D298, to be about 125 kcal. Other band systems were reported by Johnson and Jenkins3 and some were analyzed by Eyster.4 The emission spectrum of SiFzin the region 22002500 A. has been observed by Johns, et aL5 A more recent investigation of the spectrum in the region between 2180 and 5260 A. has been made by Dasari and TTenkateswarlu.6 Their anajysis of the band system in the region 2755-2179 A. shows that the SIR molecule is non-linear and the molecular parameters of the lower electronic state are: (1) angle FSiF = 124 i: 2'; ( 2 ) bond length Si-F = 1.49 0.07 A. Compilations of thermodynamic functions for SiF2based on estimated molecular parameters are available in the JANAP Thermochemical Tables.' which also report the heat of formation at 298'K. to be -118 i 10 kcal. mole-' from bond energy arguments. The experimental data of Pease' may be used tc, determine a heat of formation based 011 the reaction
+
Si(c) -t- SiFa(g)
2SiFs(g)
at various pressures and temperatures. Although there is some trend with temperaturc, as shown in Table I, the heat of formation of SiF2must fall in the range -148 A 4 kcal. mole-'. From this heat of formation of SiFzone computes the average energy of an Si-F bond as 148.5 kcal. This value is in fair agreement with the average bond energy calculated from the new heat of formation of (1) I). C. Peaae, U.S. Patent KO.2,840,588, June 24, 1938. (2) J. W. C. Johns and R. F. Bailow, P r o c . Phuo. SUC.(London), 71, 470 (1958), (.I) R . C. Johnson and 11. C . Jenkins, PTUC. R o y . Soc. (London),116,
327 (1927). (4) E. €1. Eyater, P h y s . Reu.. 61,1078 (1937). (5) J. W. C. Johns, G. W. Chantry, and R. F. Barrow, Trans. Faraday Soc., 64, 1589 (1958). (6) R. R. Dasari and P. Venkateswarlu, J . M o l . Spectroscopy, 7 , 287 (1981). (7) "JANAF Thermochemical Data," Volume 2, December 31, 1980. USAF Contract KO.AF 33(616)-G149, Advanced Research Projects Agency. Washington 25, D. C.
