1648
Brtrcs G. HOBROCK AND I ~ O B W. EI&EH ~~T
Vol. 66
E LLECTROS IMPACT SPECTROSCOPY OF SULFUR COMPOUXDS. I. %THIABUTANE, %THIAPENTANE, AND ~,3-DITHIABUTASE1 BY BRICEG. HOBIXOCK AND ROBERT W. KISER Department oj" Chemistry, Kansus State Unzvemity, Manhattan, Kansas Recemed March 8 , 1961
The appearance potentials of the principal ions in the mass spectra of 2-thiabutane, 2-thiapentane, arid 2,5'-dithiabutane are reported. Assignments of the probable processes of ionization and dissociation are made consistent with the observed energetics. Heats of formation for the various ions are computed and tabulated. From appearance potential data, (1) the ionizatian potentials of 2-thiabutane, 2-thiapentane, and 2,3-dithiabutane are 8.70 Z!G 0.10, 8.80 Z!G 0.15, and 9.1 f 0.2 e.v., respectively; (2) the proton affinities of H2S and CHa8H are -195 i: 7 and -201 i 10 kcal./mole, respectively; and (3) the derived ionization potentials of Sz and CH& are 11.0 Z!G 0.2 and 9.5 dz 0.5 e.v., respectively. Gas-liquid partition chromatographic analysis of 2-thiaIntroduction butane and 2,3-dithiabutane revealed no impurities. The Organic sulfur compounds are of considerable analysis of 2-thiapentane revealed approximately 2 mole interest in petroleum technology. The electron % imprrity of higher molecular weight. It is believed impact study of such molecules can provide that this small impurity affected neither the mass spectral cracking pattern determinations nor the appearance potensignificant information concerning these sulfur tial measuremente. compounds and their gaseous ions. Gallegos and Mass spectra were obtained a t nominal electron energies K i ~ e r ?recently ~ have reported ionization poten- of 70 e.v. The voltage scale in the determination of tials and heats of formation for a number of ions ionization and appearance potentials was calibrated using mixed intimatelv with the compound under investifarmed from various saturated heterocyclic sulfur xenon gation. The extrapolated voltage difference methoda compounds. The ionization potentials for a few was used for determining appearance potentials. Ioniaaof the straight-chain sulfides and disulfides have tion potentials also were determined using the technique been reported, but no detailed investigation of the of Losuing, Tickner, and Bryce,7 and were checked by appearance potentials and heats of formation of means of the energy compensation method.* the various ionic products of the ionization and Results dissociation process has been made. We have, The mass spectral cracking patterns and aptherefore, initiated a program to study a number pearance potential data for the three compounds of the sulfur compounds by electron impact meth- investigated are given in Tables 1-111. The relaods. tive abundance of the principal ions formed a t In this paper we report information obtained in 70 e.v. is given in column 2 . The measured a study of three sulfur-containing molecules: 2- appearance potentials are summarized in cdumn 3 thiabutane, 2-thiapentane1 and 2,3-dithiabutane. and the probable processes for the formation of the We have determined mass spectral cracking pat- ions are given in column 4. The heats of formaterns for these compounds and find good agreement tion consistent with the proposed processes for the with the data reported in the API tables.4 (Serial various ions are given in the last column. numbers 473, 476, 496, 498, 588, and 913.) IonThe heats of i'ormation of the sulfur-containing aation and appearance potential data were de- inolerules were determined by the U. S. Bureau termined for the principal ions formed from these of Riliries workers and were employed consistently three sulfur compounds. The measured ionization in all of the thermochemical calculations. 'l'hc potentials are compared to those calculated using heats of formation for 2-thiabutane,@ X-thiapeiia group orbital treatment and interaction param- tariell" arid 2,3-dithiabutane11 are - 14.22, eters previously given.3 From the experimental 19.51, and -5.75 kcal./mole, respectively. The data, the proton affinities of hydrogen sulfide arid heats of formatiorr of various radicals involved iii methanethiol are calculated. the dissociation processes were taken from those sunimarized by Gallegos. Experimental The experimental data reported here vere obtained using a time-of-flight mass spectrometer with an analog output
system. The instrumentation has been described previously.6 The samples of 2 thiabutane and 8,3-dithiabutane were obtained from Eastmari Organic Chemicals. The 2thiapentarie was obtained from Aldrich Chemical Co. (1) This work was supported by the U. S. Atomic Energy Comniis-
sion under contract No. AT(ll-1)-751 with Kansas State University. A portion of a dissertation to be presented by B. G. Hobroek to the Graduate School of Kansas State 1:niversity in partial fulfillment of requirements for the degree of Doctor of Philosophy; presented a t the 141st National Meeting of the American Cheniioal Society, Wasbington, D C., March 20-29, 1962. (2) E. J. Gallegos and R . 5%'. Kiser. J. P h w . Chem., 66, 1177 11961). (3) E. J. Gallegos and R. W. Kiser, ibid., 66, 136 (1902). (4) " M a s s Spectral Data," American Petroleum Institute Researcli Project 44, National Bureau of Standards, Washington, D. C. ( 5 ) E. J. Gallegos and R. W. Kiser, J . Am. Chem. Soc., 83, 773 (1961).
Discussion Ionization Potentials.--The ioniza tioii potentials determined for the three molecules investigated are shown in Table IV, where a comparison with other experimental results and calculations using (6) J. W Warren, n ' a t w e , 165, 811 (1950). (7) F. P. Lossing, A. W. Tickner, and W. A. Bryce, J . Chem. PJws , 19, 1254 (1951). ( 8 ) E. J. Gallegos and R. W.Kiser, J. P k y s . Chem., 6 6 , 947 (1962). (9) W. N, Hubbard a n d G. Waddington, Rec. trav. ehzm., 73, 910 (1954). (10) W. K. Hubbard, W. D. Good, and G. Waddington, J. Phys. Chem., 62, 614 (1958). (11) W. N. Hubbard, D. R . Doudin, J. P. XcCulloudi, I). a'.Scott, 8. S. Todd, J. F. Messerly. I. A. Hossenlopp, A. Gcorge, and G. Waddington, J . Am. Chem. Sor:., S O , 3547 (1958). (12) E. J . Gallegos, "Mans Spectrometric Investigation of Saturated Heteroc~-clics,"Doctoral Dissertation, Kansas State University, Manhattan, Kansas, January, 1062.
i649 TABLE I &fASS SPECTRUM R K D L4PPBiARANCE POTENTIALS OF THN PRINCIPAL IONS O r 2-THlABUTANE .m/E
Relative
Appearanoe
abundanoe
potential (o.v.)
7.8
15 26
9.7
27 29 34 35 41 44 45 46 47 48 49 57 58 59
42.4 21.9 3.5 16.4 5.8 4.2 24.4 I1 6 36.5 55.6 5.8 2.6 4.8 6.7
60 61 62 63 75 76 77
3.1 100.0 4.0 4.4 3.8 58.4 3.6 2.5
78
AHr+,
CsHaS + CHI ( ? )
17.6 i 0 . 5 17.8 f .5
+ CH, + SH + Hz + CHI + Has + H + CHIS + Ha + CH3 + S + H3S+ + CHz + CaH? + H +
332 315 316 225
C%Hz+ CzHz+ + CaHa+ -+ CzHs'
-+
16.0 f .4 14.1 i .2 1 5 . 1 f .2
15.9 f 13.6 i 14.7 i 11.8 f 12.0 f
koal./mole
Process
160
+ CzH4 + H f Hz + CzHs + H + CHI + CHa + CaHa + Hz CHoS+ + CzHz + H
287 225 226 204 157
CHS' CHzS+ + CHaS' 4 CH,S+
.4
4
.3 .2 .2 .3
.-f
4
13.4 i . 4 + CzHB'
11,si .2
+ CH,
225
8.70 f 0.10
TABLE I1 MASSSPECTRUM AND APPEARANCE POTENTIALS O F m/e
15 26 27 29
35 3!) 40 41
1% 43 45 46
Relative abundance
THE PRINCIPAL I O N S O F
8.8 3.3 34.7 7.0
16.6 i 0 . 5
10.5 17.9 3 .3 36.6 13.5 "7.0 22.2 10.2
15.6 i . 3 18.4 i . 5
Process
C4HloS -+ CHs +
15.8 i .4 15.3 It . 5
14.8 f 12.5 =k 12.3 ir 15.2 f 14.1 It
.2 .3 .4
.4 .3
58 59 6I 62 63
75 89 90 9n 92
21.7 45.5 23.7 4.1 3.4 100.0 8.7 4.7 12.0 1.1 47.7 3.3 2.3
+ (?)
--+
+ + + + + C3H5" f C H I + SH + Ha (1) CIHs" + CH, + S (13H7'. f CH3S CHS+ + C3H6 + H + Ha CHzS+ + C3H5 + H + Hz CHzS+ + CH3 + CzHb CHIS+ + CzHs + CHz CHiS+ + CaHa + CHI CHSS++ C2Hz + CHD
-+
-+ +
--+ -+
+ +
+ + + +
285 233 235 174 277 223 234 226 274 222 252 214 205 147
14.0 f . 2 11.3 f .2 11.0 =k . 2
+
1 1 . 9 f .2
+.
CzH&'
+ CzHj
233
11.7 f . 2
+
CsH7S'
+ CHs
219
-+
CdHioS+
8.8 f .15
the group orbital methodI3 is made. I t is seen that the ionization potential we det'ermined for 2(13) J. L. Franklin,
koal./mole
CzH3.'- f CzHd HzS H CzHs-'. CzHa HrS H 4 CzHs'. CH3 SCHs -+ H3S" CHz C3H4 H -+ C3Ha.k $. CHIS f H 2Hz
-+
-+
47 48 49
2-THIAPENTANE AHP,
Appearance potential (0.v.)
J. Che?n. Phys., 22, 1304 (1954).
---*
-+
184
t'hiabutane is in good agreement with the ot'her result reported in the literature and with the calculated value. The ionization potential for 2-
BRICEG,BOBROCK AND ROBBRT W. KISER
1650
Vol, 66
the electron impact method with argon as the calibrant gas. We could not, however, obtain a value lower than 8.9 e.v. for the ionization potential in any determination. We do not have an explanRelative Appearance ation for this apparent discrepancy. AHf+, abund- potential kcal./ m/e = 15.--In each of the three molecules W'E ance (e.v.) Process mole studied, the m/e = 15 ion is CHB+. We have 15 1 4 . 0 15.7 i 0.3 CzHaSz CHa" (?) determined and reported in Tables 1-111 the ap44 3.5 pearance potentials of the m/e = 15 ion in each case, 45 58.6 15.5 i . 3 CHS" + CI-148 + H 299 46 39.5 12.2 .2 CHeS" 4- CH4 + S 240 but we are not able to arrive a t a singular process 47 27.4 13.0 & . 4 CHsS' + CHsS 255 for their formation since energetic considerations 48 14.8 11.5 It . 2 -* CHaS+ + CS + Hz 205 indicate that a number of processes may contribute. 49 5 . 3 11.9 Zk . 2 CHsSt 4- CS + H 175 m/e = 26.-From 2-thiabutane, the only ion of 61 16.7 10.9 i . 2 CzHaS" + SH 213 m/e = 26 that could be formed is CzHz+and we 64 9 . 6 15.4 i . 3 Set + 2CHs 285 78 3.1 find that two processes could be involved in its 79 54.3 12.1 32 . 2 + CHaSz+ + CHs 240 formation. The processes are those shown in 80 2.6 Table I . The first involves the formation of the 81 4.9 neutral fragments CH3 SH Hz and thus AHf+93 1.9 94 100.0 9 . 1 i . 2 CHsSSCHa" 204 (CZHZ) = 332 kcal./mole. The second process 95 5.6 provides for the formation of CHs H2S H 96 9.3 and has AHf+(C2H2) = 315 kcal./mole. Both thiapentane agrees with the calculated value. KO are in fair agreement with the value of 317 kcal./ previous experimental determination of the ioni- mole given by Field and Franklinle and it is not possible to differentiate between the two processes. zation potential of 2-thiapentane has been made. m/e = 27.-The ion of m/e = 27 is C2H3f and is Our value of 9.1 0.2 e.v. for the ionization potent'ial of 2,3-dithiabutane does not agree very believed to be accompanied from 2-thiabutane by Hz. The heat of well wit,h the experimental result of 8.46 e.v. the neutral fragments CH3S det'ermined by the photoionization method.I4 formation of this ion for this process is 316 kcal./ Using Watanabe's value of 8.46 e.v., we calculate mole. This is high in comparison to the literature an S-S interaction parameter of 1.14 e.v., and value of 280 kcal./mole,16 but it is the most reasonusing this, we further calculate an ionization po- able process for the formation of this ion from 2tential of 8.36 e.v. for 3,4-dithiahexane. This thiabutane, as is shown by the energetics. From 2-thiapentane1 this ion is observed with calculated value agrees with the 8.27 e.v. reported H2S H , by Watanabe.14 (We note that d(S-S) = 1.32 the accompanying formation of CzH4 if 8.27 e.v. for 3,4-dithiahexane is used to evaluate according to the energetics. AHf+(C&) = 285 kcal./mole is calculated. This agrees with the TABLEIV value determined for this ion from 2-thiabutane. m/e = 29.-The formation of CzH6+from 2MOLECULAR IONIZATION POTENTIALS OF S o m SULFUR thiabutane appears to occur by the process shown COMPOUNDS in Table I. The heat of formation of this ion acc-Ionization potential (e.v.)cording to the proposed process is 225 kcal./mole. Molecule Calcd. hleasd. b This is in good agreement with the literature value 3.. 0 of 224 kcal./mole.l6 1.99h d In the study of 2-thiapentane, the energetics 1.14 e indicate two equally plausible processes for the 13.31' formation of the m/e = 29 ion. These are shown r 10.46' in Table 11. Another possible process would he CE1,SII (0.44) 9.44d CdliloS-+ CzH5+ C€Iz CH3S. Considcring CH,-S-C&CEIa 8.65 8.55d 8 . 7 @ the uncertainty assigned l o the determined apCI13-S-CHz-CIIZC€Ia 8 . 6 4 8 .SOe pearance potential, the average AH+(CzHs) = CI-Ia-S-S-CHS (8.46) 8.46d 8.53' 9.1' 234 kcal./mole, calculated, is in good agrecmcnt C€IZCHz-S-S-CH&€Ia 8.36 8 . 2'id a These parameters are given b y Pranklin.18 See ref. 2. IC. lvith the literature16 and the value determined from 2-thiabutane. Watanabe, J . Chem. P h y s . , 2 6 , 542 (1957). See ref. 14. e D a t a See ref. 15. reported in this work. m/e = 35.--The ion of m/e = 35 can only be W3S+,analogous to H30+, and must be formed as d; this leads to I(2,3-dithiabutaiie) = 8.34 e.v.) a result of rearrangement. The neutral fragments Since the electron impact ionization potentials formed from 2-thiabutane are believed to be CH2 correspond to vertical transitions according to the CzHz H; therefore AHf+(HaS) = 160 kcal./ Franck-Condon principle, it would be better to mole. compare our results to values determined by others From the 2-thiapentane study, the appearance using mass spectrometric methods. A value of potential of 15.6 f 0.3 e.v. for this ion leads to 8.53 e.v. for the ionization .potential of 2,a-dithia- AHf+(H3S) = 174 kcal./mole if the neutral fragbutane has been reported by Varsel, et aZ.,15 using T.?BLE 111
MASS SPWCTRUM AND APPEARANCE POTENTIALS OF TIJE PRINCIPAL Iom OF ~,~-DITHIABUTANJI
+
-+
+
-+
4
-* -+
+
+
4
+
+
+
+
+
+
+
f
+
(14) K. Watanabe, T. h'akayama, and J. Mottl, "Final Report on Ionization Potentials of Molecules b y a Photoionization Method," December, 1959. Department of Army B5B99-01-004 ORD-#TBZ001-00R-Wl624. Contract No. DA-04-200-0RD 480 and 737.
+
(15) C. J. Varsel, F. A. Morrell, F. E. Resnik, and VI. A. Powell, Anal. Cham., 32, 182 (1960). (16) F. H. Field and J. L. Franklin, "Electron Impact Phenomena and the Properties of Gaseous Ions," Academic Press, Inc., New York, N. Y . , 1957.
ELECTRON IMPACT SPECTROSCOPY OF SULFUR COMPOUTU’DS
Sept., 1962
+
ments are iCHz 4- Cy& €1. ‘The results are in reasonably good agreement ; an experimental heat of formation of this ion has not been reported previously. The ionization efficiency curves for this ion from both molecules mere found to resemble closely an ionization efficiency curve for a parent molecule-ion, each having a small “foot.” The average Allr+(€13S)is 167 kcal./mole. This leads to a proton affinity of H2S of 195 f 7 kcal./mole, using AHf+(H) = 367 kcal./mole and AHf(H2S) = -4.8 kcal./mole. Lampe and Field17.1s have studied the reaction of the HzS+ion with both HzS and CH, to form H3S+. Assuming that these reactions have a zero heat of reaction, one calculates the heat of formation of H:8+ to be equal to or less than 186 kcal./mole. This substantiates our average value of 167 kcal./mole. Lampe and Field also give an approximate value of >175 kcal./mole for the proton affinity of HzS. This tends to substantiate our value of 195 f 7 ked./ mole. The determination of a more accurate value from additional data is presently underway in our Laboratories, and hopefully will lead to a reliable proton affinity for hydrogen sulfide. m/e = 39.-Tlze C3H3+ion was observed in sufficient quantity t o allow an appearance potential determination only in the 2-thiapentane spectrum. Energetic considerations lead to a choice of CHzS H 2H2 as neutral fragments, and therefore we calculate a value of AHf+(C3€13)= 277 kcal./ mole, in reasonable agreement with other determination~.~~ mfe = 41.-C3H5+ also was observed only in the 2-thiapentane spectrum in quantities sufficient for appearance potential measurements. The process given in Table I1 is considered reasonable, leading t o AHf+(C3H5)= 223 kcal./mole; however, another process which is possible is the formation of this ion accompanied by CS 2Hz H as the neutral fragments, leading to AHf+(C3H5)= 2 17 kcal ./mole. mfe =
