June, 1963
ELECTRON IMPACT IWESTIGATIOB OF SULFUR COMPOUNDS
the hydrogen bond and migrates between the H-bonded molecules in the crystal lattice. The mechanisms advanced above for surface con-
1283
ductivity are nearly equally probable. Additional experiments would be required in order to clarify which of them is the predominant one.
ELECTRON IMPACT ISVESTIGATIBNS OF SULFUR COMPOUKDS. 111. 5!-TRIAPROPAI\'E, 3-THIAPENTANE, ASD 8,3,4-TRITHIAPE;\'TANE1 BY BRICEG. HOBROCK ASD ROBERT W. KISER Department of Chemistry, Kansas State University, iWanhattalz, Kansas Received December 19, 1962 I n addition to reporting basic electron impact data for 2,3,4-trithiapentane, 2-t hiapropane, and 3-thiapentane, comparisons of heats of formation of various series of related ions containing one, two, and three sulfur atoms are made. It is observed that, in general, successive addition of sulfur atoms has little effect on the heats of formation of the ions. This is also found to be true for variation of the R group. The addition of hydrogen atoms is observed, in almost all of the cases we studied, to have a significant effect in decreasiing the heats of formation of the ions. The heats of formation for the principal ionu from the three compounds in agreement with postulated processes, are given. The ionization potentials of the molecules are discussed as well as the derived values for the ionization potentials of C2H6SH and CHaSzH. spectrum and relative vapor pressures confirni this amount of :Introduction impurity. After standing on the inlet system of the mass specIn t'he course of our study of the ions resulting from trometer for a short period of time, the impurity in the 2,3,4the ionization and dissociation of organic sulfur conitrithiapentane became quite small and no interference was notaed pounds by electron impact in a mass s p e c t r ~ m e t e r , ~ - . ~in the subsequent measurements of appearance potentials. Appropriate subtraction of impurities from the mass spectrum we have noted many unusual and interest'ing species. obtained gave results which agreed very closely with serial 1222 In our initial studies, we paid particular attention to in the API Tables7 dletermined from the same sample by S. the ease with which hydrogen atoms rearrange onto Meyerson. Good agreement was also obtained with serial 9'09 sulfur atoms (ie., HB+, CHbS+, H&+, etc.). In an and serial 497 for 2-thiapropane and 3-thiapropane, respectively. attempt to observe and study more of these intriguing Results and Discussion species, such as HzS3+,CH3S2H+,CH3S3H+, and Ss+, Heats of formatioii for the various ions in accord we have studied 2,3,4-trithiapentane. Kot all of the with their respective postulated processes are listed species just cited were observed experimentally; in Tables I, and 11 and III. The experimentallly however, a number of other different ions were found. measured appearance potentials and partial mass specWe describe herein our methods of study and the results tra are also given. The calculated heats of formation observed and then we discuss these latter ions. I n are based upon the appearance potentials, the approaddition, we also include new electron impact data for priate heats of foirniation of the molecules, and the 2-thiapropane and 3-thiapentane. Appearance poproposed radicals. The heats of formation employed tentials for the positive ions of interest are measured for 2-thiapropane and 3-tliiapentane were - 8.7'9* and probable ionization and dissociation processes are and - 19.77 kcal. respectively. The calculngiven in agreement with heat of formation data. Heats tions for 2,3,4-trit':hiapentaiie are based, however, on of formation of the ions are calculated and intracomour estimated value for its heat of formation of 0.0 parisoiis are made and discussed for various series of kcal./mole. This estimation was made by extrapolarelated ions. tion from values for 2-thiapropane and 2,3-dithiabutane. Experimental Good agreement with known or previously determined The experimental techniques employed are the same as those heats of format'ion for ions are obtained using this value. described p r e v i o u ~ l y . ~ -The ~ samples of 2-thiapropane and 3A heat of formation of 51 kcal./mole for CHzS has beon thiapentane were obtained from Aldrich Chemical Co. and were employed. This value is 25 kcal./niole less than that used as received. Gas-liquid partition chromatography sugused by Gallegos and Kiser. lo gested that both compounds were pure; however, a small nonThe ionization potent'ials determined for the three sulfur-containing impurit,y was noted in the mass spectrum of 3thiapentane. The only interference with the mass spectrum of 3compounds in this study agree very well with liter,athiapentane was noted a t m/e = 58; however, this was not a Oure values. The value of 8.70 e.v. for 2-thiapropane serious interference. The sample of 2,3,4-trithiapentane was agress closely with 13.73 e.v. determined by Issacs, et al. very graciously supplied to us by S. Meyerson of American and 8.684 e.v. determined by WatanabelZ by photoOil Company, Whiting, Indiana. An impurity of about 27, 2,3-dithiabutane was noted6 and our calculations from the mass (1) This work was supported b y the U. S. Atomic Energy Commission under contract No. AT(11-13-751 with Kansas State University. This is a portion of a dissertation t o be presented b y B. G. Hobrock to the Graduate School of Kansas State University in partial fulfillment of the requirements f o r the degree of Doctor of Philosophy. Presented a t the 144th Kational Meeting of the American Chemical Society, Loa Angeles, California, March 31, 1963. (2) B. G. Hobrock and R. IV. Kiser. J. Phys. Chem.. 66, 1214 (1962). ( 3 ) B. G . Hobrock and R . W. Kiser. ibid., 66, 1648 (1962). (4) B. G. Hobrock and R. W .Kiser, ibid., 67, 648 (1963). ( 5 ) E. J. Gallegos ana R . W.Kiser, J . A m . Chem. Soc., 83,773 (1961). (6) S. Rleyerson, private communication.
(7) "Mass Spectral Data," American Petroleum Institute Research Pr'ojtect 44, National Bureau of Standards, Washington, D. C. (8) J. P. McCullough, W. N. Hubbard, F. R. Frow, I. A. Hossenlopp, a n d G . Waddington, J . Am. Chem. Soc., 79, 561 (1957). (9) TV. N. Hubbard, W.D . Good, and G. Waddington, J . Phys. Chem., 62, 614 (1958). (10) E. J. Gallegos and R . W.Kiser, ibid., 66, 136 (1962). (11) L. D. Issacs, W. C. Price, and R. G. Ridley, "Vacuum Ultraviolet Spectra and Molecular 1on.ization Potentials," in "The Threshold of Space," edited b y R I . Zelikoff. Pergramon Press, Ltd., London, 1957, pp. 143-151. (12) K. Watanabe, T. Xakayama, and J. blottl, "Final Report on Ionization Potentials of Llolecules by a Photoionization Method," December, 1959. Department of Army KO.5B99-01-ll5 O R D TB2-001- 00R-1824. Contract KO.DA-04-2000RD 480 and 737.
BRICEG. HOBROCK ASD ROBERT W. RISER
1284
Vol. 67
TABLE I APPEARANCE POTENTIaLS m/e
70 e.>-. R.E.
13 14 15 27 29 34 35 37 44 45
2.1 7.6 14.0 25.0 1.5 1.3 32.0 1.3 5.1 51.9
AND
HEATSO F FORMATION O F THE
PRINCIPAL I O N S FROM
A.p. (e.v.)
Process
+ CHz + SH + H + HsS
17.0 f 0 . 4 15.4 i 0 . 3
C2HsS + CHa+ -C CzH3+
14.8 f 0 . 2
+ HIS'
15.0 i 0 . 5 (?) 15.6 f 0 . 2
+ CHSf
42.0 100.0 3.1 4.7 2.6 3.4 3.1 32.5 83.0
11.2 & 0 . 2 11.7 i 0.2
+
+ CH, + H ( ? ) + CHI + Hz ( ? )
CH2S+
+ CHI (1) + CH3
+ CHBS+
11.8 f 0 . 2 8.70 f 0.20
-+
+
284 299
+ (111)
+ CHS+
46 47 48 49 57 58 59 61 62
2-THIAPROPANE
+
CPHSS+ H CzHsS+
317
229
211 192
TABLE I1 APPEARAXCE POTENTIALS AKD HEATS O F FORMATION O F THE m/e
15 26 27 29 34 35 41 45 46 47 48 49 57 58 59 60 61 62 63 64 75 76 77 89 90 92
70 e.v. R.a.
3.6 18.0 91.1 62.7 4.3 18.0 6.4 32.9 16.4 82.4 2.1 4.2 5.6 16.0 ( 1 ) 11.7 11.1 59.1 56.2 3.8 1.9 100.0 3.2 6.2 2.5 60.4 2.3
PRIKCIPAL I O K S O F
3-THIAPEXTANE
anf.b A.p. (e.v.)
16.3 i 0 . 5 16.7 f 0 . 5 14.5 i 0 . 3
(kcal./mole)
Process
CiHioS
+ +
+ +
CzH3+ CzHj C P H ~ CzHs
+ 2CpHa + H CHS+ + CzH4 + CHa + H2 (1) CHzS+ + CzHj + CH3 CHIS+ + CH3 + C2H4
15.6 & 0 . 4
+ Has+
15.3 f 0 . 5 12.5 f 0 . 3 13.5 i 0 . 2
+
6
-+
+ S + H? +S
+ CH3 + CH? + Hz + CzH4 + HP + C?Hj
160 289 215 247
14.6 i 0 . 4 11.2 i 0 . 2 12.0 5 0 . 2 10.4 i 0 . 2
CpHiS+ + CsHaS+ -C C2HeSf
+ CzHi
217 226 235 208
11.6 f 0 . 2
+ CaH,S+
+ CHa
216
8.49 & 0.19
+C4HiaS
ionization techniques, but poorly with a value of 9.4 e.v. determined by Sugden, et aZ.,13 by electron impact methods. A calculated value of 8.73 e.v. by Gallegos and Kiser14 is also in agreement. For 3-thiapeiitane, our value of the ionization potential of 8.49 e.v. agrees wit'h literature values of 8.43 e.v.ll and 8.48 e.v.12 and with a calculated value of 8.58 e.v.I4 The ionization potential for 2,3,4-trithiapentane of 8.80 e.v. which we report here is new and appears to be a quite reasonable value. One may attempt to calculate the ionization potentials of some other trisulfides (13) T. M. Sugden, A. D. Walsh, and TV. c. Price, Nature, 148, 373 (1951). (14) E. J. Gallegos and R. W. Kiser, J . Phgs. Chem., 65, 1177 (1961).
+ C1HaS+
290 239
+
+
176
by an equivalent' orbital method2z3,16 but results are inconclusive as the values are very sensitive t o small changes in the ionization potent'jal selected for H2Ss. The calculation is based upon an interpolated value for t8heionization potential of this molecule. Other ionization potential data may be derived from our experimental results. From 3-thiapentaiie, the ion at m l e = 62 is C2H6S+but probably has the structure C2&SH+ for reasoils t o be discussed next. Using a heat of formation of -11.03 kcal./mole for the molecule8 and our heat of formation for the joii of 207 kca1.l mole, the io11ization potential of C2H6S+is calculated to be 9.45 e.v. which agrees with 51 1it'eratUre Value Of (16) J. L. Franklin, J. Chem. P h w , a%, 1304 (1964).
ELECTROK IMPACT INVESTIQATIOS OF SULFUR COMPOUNDS
June, 1963
APPEARANCE POTEXTIALS
AND
TABLE I11 HEATSO F FORMATIOX O F THE PRISCIP.4L IONS O F 2,3,4-TRITHIAPENTANE
70 e.v.
R.a.
15 32 44 45 46
7.9 4.1 2.5 59.0 21.3
47 48 61 64 65 66 78 79 80 81 111 126 128
35.9 2.4 7.9 22.3 2.2 2.5 7.0 50.6 14.1 3.4 16.2 100.0 10.5
1285
A p . (e.v.)
14.5 f 0 . 3 13.4 0.3 12.9
AHf" (kcal./rnole)
Process
CHaSSSCHs 4 CHS+
+ CH3 + Sz + Hz
272
=I= 0.2
14.4 f 0.3
12.3 f 0.2 10.8 f 0.2
246 198
11.4 f 0 . 2 8.80 0.15
231 203
*
I(CzH5SH)= 9.285 e.v.12 Therefore, the structure of the ion. is believed to be C~HSSH+,instead of CH3SCH3+, which has mi ionization potential of 8.70 e.v., as reported above. One may also attempt to derive an ionization potential for the ion at m / e = 80, CHdSzf, from 2,3,4-trit hiapentane. One may estimate a heat of formation for the CH3SSH molecules of --5 kcal./mole, using Franklin's method.It6 Csing AHf+(CH3SSH) = 198 kcal./mole, one may calculate an ionizat'ion potential of 8.8 e.v. An equivalent orbital calculation4 gives a value of 9.15 e.v., in fair agreement with the value derived from our data. If one assumes that the neutral fragments are C8 Hz, AHf(CH3SSH)= 196 which leads to I(CH3SSH) = 8.7 e.v. Correlations of Heats of Formation Our observations of the various species in the mass spect'rum of 2,3,4-trithiapentane allow us to make a number of correlations of heats of forniatioii of various series of related ions (see Table IV). Since we observed Sz+from CH3S2C,H3, it was hoped that the S3+ ion might be observed from 2,3,4-t:rithiapentnne. However, S3+ did not appear in the mass spectrum of 2,3,4-trithiapentaiie; this ioii may well be too unstable to exist in the gas phase. An examinatioin of the lit,eraturel7 reveals t'hat S3+ exists in aqueous solution, but no information coiicerniiig S3 and S3+ is available. By extrapolation using the knosvii AH,+(S) = 30418 and AHf+(SS) = 282 (see Table IV) a value of approximately 260 kcal./mole is expected for AHf+(S3). Similarly, one can extrapolate AHf(S) and AHf(S2)to obtain AHf(S3)= 7 kcal./niole. Combination of these estimates leads one to estimate I(&) = 11.0 e.v. The addition of hydrogen atoms to the S i - , Sz+,and SS+series appears to stabilize the AHf a t a nearly con-
+
(16) J. L. Franklin, Ind. Eng. Chem., 41, 1070 (1949). (17) F. D. Rossini, D. D. Wagman, W. H. Evans, 9. Levine, and I. Jaffe, "Selected Values of Chemical Thermodynamic Properties," National Bureau of Standards Circular 500, U. S. Government Printing Office, Washington, D. C., 1952. (18) F. H. Field and J . L. Franklin, "Electron Impact Phenomena and the Properties of Gaseous Ions," Academic Press, Kew York, N . Y., 1957.
TABLE IV COMPARISONS OF THE HEATSOF FORMATION OF RELATED IONS Species
' S S2
+
S3 HzS HzSz HZS3 CHaS+ CHiSz + CHsS3+ CHISH + CHsS2H + CH&H CHsS CzHtS + CrH7S CHaSH + CzHsSH + CsH?SH+ CHaSzH -t C2HBzH + CdH7SzH + CHS + CHzS + CHIS+ CHiS + CHsS + CzHzS + C2HrS + C2H:S + CzHsS + CzHsS + C2H7S' +
+
+
+
+
+
"best." AHf +, kcal./mole
304 282 (255) 236 239 (242) 226 229 23 1 205 1'38 ( 1'30) 226 225 217 205 207 (200) 1'38 219 (216) 2'70 225 226 205 183 284 234 226 225 192-208 (1'75)
CH3SCzHs CzHsSzCzHj CH3S3CH3 CHaSzCHa, CHsSn-C3H1 CHaS3CHa
st ant value. This is not too surmisine: when one notes also the addition of hydrogen ;toms-in the CS+ and CzHzS+ series (see Table IV) . The series, CH3S+, CH,Sz+, CH3S3+, wasco mpleted in this study as CH3S3+ occurred in the mass spectrum of 2,3,4-trithiapentnne. The decreasing value for th.e heats of formatioii of the S+, Sz+,S3+ series apparently is arrested by the addition of a CH3 radical. We note that the series experienced only a very minor (and
SURESHK. GUPTXA K D
1286
possibly unreal) increase. We conclude that the subsequent addition of one or two sulfur atoms has little or no effect on the A H f +of the ions of the CH3Sm+type. CH3S3H+ was not observed. By comparison to CH3SH+ and CH3S2H+, it would appear that if the trend is followed, the heat of forniatioiz of CH&H+ might be slightly smaller than for CH3SH' and CH3S2H+. We note also that in the other series, the addition of H atoms to sulfur atoms results in ions with lower heats of formation. AHf+(CH3S3H) is estimated to be -190 kcal./mole. It is anticipated that CH3S3H+ may be experimentally observed in planned studied of 3,4,5-trithiaheptane or 2,3,4-trithiahexane. The effect of changing the R group also is noted in the series CH3SH+, C*HhSH+, and C3H7SH+. S o A H f + (C3H,SH) has yet been calculated but the ion has heen observed in significant quantities in n-propyl and isopropyl sulfides. It is estimated, however, that AHf+(C3H7SH) = 200 kcal./mole. Again, we see no significant effect on AHf+for these ions when changing R. The value of 216 kcal./mole for AHf+(C3H&H) has not been previously reported but was determined from 4,5-dithiao~tane.~~ With reference to the various preceding series, one would expect that the heats of forinstion of these ions would remain constant around 215 kcal./mcle. If AHf+(CH3S2H)were then also 215 kcal./mole, the ionization potential of CH3SaH (19) B. G. Hobrock a n d R.
W.Kiser, unpublished results, 1962.
RICHARD
F. P O R T E R
Vol. 67
then is calculated to be 9.23 e.v., in good agreement with the calculated value of 9.15 e.v. discussed earlier. The effect of adding successive hydrogen atoms to CS+ is shown and, as in most of the preceding series, it is noted that the heats of formation of the ions become smaller. Large decreases in AH*+ are found for CHS + and CHlSf. KO apparent decrease in AHff is seen for CH2S+ 2 CH3S+,as the heats of formation are essentially the same. Addition of an H atom to CH3S+ and C H B + then again continues the trend to lower AHf+. The same type of series is investigated by noting successive addition of H atoms to C2H2S+. The same trends are dominant as in the preceding series; lower AHf+for C?H3S+and C?H4S+,but the heats of formation for C2H4S+and C2H6S+are alike. And again, + lower A H f + subsequently are found for C ~ H B Sand CrHiSf. The value of 175 kcal./niole for AHff(C2His) is an estimated one. We plan to be able to report experimental data for this ion in a future publication, since it has been observed in measurable quantities in both C2H5Sn-C3H7and C2HjSi-C3H,. Acknowledgments.-We gratefully acknowledge the gift of the sample of 2,3,4-trithiapentane by S.hIeyerson of American Oil Company, Whiting, Indiana, and we also wish to thank him for the details of its source and purity.
INFRARED SPECTRA OF SOLID BQRQXINE' BY SURESH K. GUPTAAND RICHARD F. PORTER^ Departinent of Chemistry, Cornell University, Ithaca, Received December 20, 1468
Y.
Solid boroxine (B3031&)has been isolated a t liquid nitrogen temperatures from the high temperature reaction products of HzO(g)with B-BzO3 mixtures. Low temperature infrared analyses of thin films of the solid may be interpreted on the basis of the six-membered ring structure characteristic of boroxine derivatives, although the spectra suggest that the atoms in the ring are not coplanar. Structural changes in the solid are noted by observing the spectra of films as they are warmed and evolve diborane. The thermal decomposition product at 25" has the approximate composition BaOjHz. Similarities in the decomposition behavior of boroxine and its trifluoro and trichloro derivatives are noted.
Introduction Mass spectrometric studies3 of the low pressure reactions of H*(g) with B-B2O3 mixtures and of HzO(g) with elemental boron have shown that gaseous boroxine, B303H3, is a reaction product a t temperatures of about 1400'K. A condensed form of boroxine has not previously been reported as an isolated compound although a number of its alkyl derivatives have been prepared. Difficulty in isolating the unsubstituted compound is noted from the observation3that the product condensed in a liquid nitrogen trap from the high temperature gassolid reaction disproportionates a t room temperature to diboraize. The present work is an outgrowth of the mass spectrometric studies and we have utilized the high temperature reaction to produce quantities of this material for chemical and structural studies. Experimental Samples of solid were obtained by condensing the gaseous product generated when HzO(g) is passed over a mixture of (1) Supported b y the Advanced Research Projects Agency. (2) Alfred P. Sloan Fellow. (3) '8. P. Sholette and R. F.Porter, J . Phys. Chem., 67, 177 (1903).
boron and boric oxide a t temperatures between 1350 and 1400'K. The reactant mixture was contained in a molybdenum boat in contact with a cylindrical piece of molybdenum foil used as a liner in a quartz reaction tube. This tube was sealed to a Pyrex vacuum system and HsO(g) was passed through a glass frit over the reactants while the pressure in the system was maintained a t about 1 mm. by continual pumping. The reaction tube was heated by a resistance-type furnace. Gaseous Ha0 reacts completely a t the high temperature and the measured gas pressure in the system is due mainly to hydrogen which is the main product in a reaction that also produces additional boron oxide. The vacuum system was constructed to permit isolation of milligram quantities of solid by passing the reaction products through a U-tube held in a liquid nitrogen trap. A further modification was the replacement of the U-tube by a low temperature infrared cell through which the product gases could pass. Solid was deposited on a 1-in. NaCl disk which was held within the cell in a copper jacket fastened to a copper block which was cooled by a liquid nitrogen reservoir. The cell was made from a piece of stainless steel tubing 2.5 in. in diameter and about 4 in. in length and was joined to the vacuum system by Kovar glass seals. The external YaC1 windows were sealed with Glyptal to the ends of the cell for vacuum-tight operation. Accumulation of moisture on the outside of the windows was observed unless warm air was passed over the cell. Under these conditions the temperature of the internal window was found to be - 150" with liquid nitrogen as coolant. Spectra were obtained with a Perkin-Elmer
