Energy & Fuels 1994,8, 1168-1174
1168
Occurrence and Identification of C33, C37, and c 3 8 Organic Sulfur Compounds in Sediment Extracts Assem 0. Barakat* Department of Chemistry, Faculty of Science, Alexandria University, P.O. Box 426, 21321 Alexandria, Egypt
Jiirgen Rullkotter* Institut fur Chemie und Biologie des Meeres (ICBM), Carl von Ossietzky Universitat Oldenburg, Postfach 2503,D-26111 Oldenburg, Germany Received April 8, 1994@
A number of structural isomers O f C33 2,5-dialkylthiophenes (I),C33, C37, C38 2,6-dialkylthianes (111, and 2,5-dialkylthiolanes (111)have been identified in sediment extracts from the Nordlinger Ries, southern Germany. The identifications are based on gas chromatography (GC) and gas chromatography/mass spectrometry (GCNS) analysis and confirmed by carbon skeleton determination on desulfurization products using Raney nickel treatment. All the organic sulfur compound classes mentioned exhibit structural distributions dominated by a limited number of all theoretically possible isomers. This provides further evidence for the formation of these compounds by abiogenic incorporation of sulfur into functionalized lipids at the early stages of diagenesis. Absence or low abundance of compounds with the same carbon skeletons in other extract fractions (saturated hydrocarbons, ketones) illustrates the specificity of this early diagenetic process.
Introduction Small sulfur-containing molecules were first detected in crude oils in the 19th these were mainly alkyl sulfides, thiophene, thiolane, and thiane. Since then, the number and structural complexity of organic sulfur compounds (OSC) identified have increased significantly. Many of the identified OSC were relatively small (with E
>= 2Q
70
.cI
. I
.cI
50
30
60
70
80
100
110
Nordlinger Ries Well-30; Depth 222.9 m Aromatic hydrocarbons
120
>
90 Retention time, min
100
E
5
I
80
0-
v)
c c
Q1 c,
-
60
,40
20 60
70
80
90
100
110
Retention time, min
Figure 1. Partial expanded capillary column gas chromatograms of the aromatic hydrocarbon fractions of samples from the Nordlinger Ries. Labeled peaks are identified in Table 1,s = 30-(2’-methylenethienyl)-l7~(H),2l~(H)-hopane. (containing 1%methanol) for 7 days. The bitumen was obtained by removing the solvent with a rotary evaporator at 30 “C and weighed. The residue was subsequently extracted with dichloromethane and dichloromethanetmethanol mixture (l:l, v/v) using ultrasonication and centrifugation. Total extracts were separated by medium-pressure liquid chromatography (MPLC) into saturated hydrocarbons, aromatic hydrocarbons (including OSC), and hetero components on a column packed with silica gel using n-hexane as e 1 ~ e n t . l ~ Desulfirization of the “aromatic hydrocarbon” fractions was carried out using Raney Ni in ethanol. Approximately 5 mg of the fraction was dissolved in absolute ethanol (2 mL) and (14)Radke,M.;Willsch, H.; Welte, D.H.Anal. Chem. 1980,52,406411.
mixed with 0.5 g of a suspension of Raney Ni (E. Merck, Darmstadt, Germany) in ethanol. The mixture was stirred and refluxed under Nz for 2 h. The desulfurized products were purified by flash chromatography over Silica gel (0.4 x 2 cm) using CHzClz as eluent (10 mL), dried, concentrated, and hydrogenated with H2/Pt02 in CH3COOH (Suprapure, Merck) at room temperature for 2 h. Gas Chromatography. Gas chromatography (GC) analysis was performed on a Carlo Erba 6180 instrument equipped with an on-column injector. Fractions (1.0 pL) in n-hexane (ca. 1-5 mg/mL) were injected onto a fused silica capillary column (25 m x 0.32 mm i d . , 0.17pm film thickness) coated with 5% phenylmethylsilicone (HP-5). Detection was accomplished by a flame ionization detector (FID). The presence of sulfur compounds in the aromatic hydrocarbon fractions was
1170 Energy & Fuels, Vol. 8, No. 6,1994
Barakat and Rullkotter
Table 1. Midchain Cyclic CSS,cs7, and C S Sulfur ~ Compounds Labeled in Figure 1" peak a
a
identification C33 midchain DATP
b
trans
C33 midchain DATN
C
cis midchain C33 DATL
d
trans midchain C33 DATL
e
cis midchain C37 DATN
f
trans midchain C37 DATN
g
cis midchain C37 DATL
h
trans midchain C37 DATL
i
cis midchain c 3 8 DATN
j
trans midchain C38 DATN
k
cis midchain C38 DATL
1
trans midchain c38 DATL
dominant components
structure Ia Ib IIIa IIIb IIIC IVa Nb Va
2-hexyl-5-tricosylthiophene 2-pentyl-5-tetracosylthiophene
2-hexyl-6-docosylthiane 2-pentyl-6-tricosylthiane 2-butyl-64etracosylthiane 2-hexyl-5-tricosylthiolane 2-pentyl-5-tetracosylthiolane 2-hexyl-5-tricosylthiolane 2-pentyl-54etracosylthiolane 2$-dihexadecylthiane 2-heptadecyl-5-pentadecylthiane 2,6-dihexadecylthiane 2-heptadecyl-5-pentadecylthiane 2-heptadecyl-5-hexadecylthiolane 2-octadecyl-5-pentadecylthiolane 2-heptadecyl-5-hexadecylthiolane 2-octadecyl-5-pentadecylthiolane 2-heptadecyl-5-hexadecylthiane 2-octadecyl-5-pentadecylthiane 2-heptadecyl-5-hexadecylthiane 2-octadecyl-5-pentadecylthiane 2,5-diheptadecylthiolane 2-hexadecyl-5-octadecylthiolane 2,5-diheptadecylthiolane 2-hexadecyl-5-octadecylthiolane
vb
IIa IIb IIId IIIe IVC IVd Vc Vd
IIC IId IIIf IIIg Ne Nf
Ve Vf
See Chart 1 for structures.
confirmed by GC with a sulfur-specific detector (FPD)held a t 200 "C. The temperature was programmed from 60 to 80 "C a t 30 "Clmin, and from 80 to 300 "C at 4 "C/min with an initial hold time of 1 min and a final hold time of 20 min. Helium was used as carrier gas. All GC data were stored and processed by a Multichrom on-line data system (VG Instrument). Gas Chromatography/Mass Spectrometry. Gas chromatography/mass spectrometry (GC/MS) measurements were carried out on a VG 7070 E mass spectrometer linked t o a Carlo Erba 4160 gas chromatograph. Samples (in ethyl acetate) were injected onto a fused silica capillary column (50 m x 0.32 mm i d . , 0.4 pm film thickness) coated with CP-Sil5. Helium was used as carrier gas; the temperature was programmed from 110 to 320 "C a t 3 "C/min with an initial hold time of 2 min and a final hold time of 30 min. The mass spectrometer was operated at an ionization energy of 70 eV. The source temperature was kept at 230 "C and the magnet scanned continuously at a rate of 2.5 &can over a mass range of m / z 45-900. All data were acquired and processed using a Kratos DS-90 data system.
Results and Discussion
Partial expanded gas chromatograms of the aromatic hydrocarbon fractions of the two studied samples are shown in Figure 1. GCMS analysis indicated that the major peaks in the high molecular weight range represent compounds with mass spectral patterns typical of those of 2,6-di-n-alkylthianes (DATN) and 2,5-di-nalkylthiolanes (DATL) possessing C33, C37, and C3a carbon skeletons. In addition, mass spectra of 2,5-din-alkylthiophenes (DATP) with 33 carbon atoms were also recorded. Peaks correspondingto these compounds are labeled in Figure 1 and identified in Table 1. Identifications are based on relative retention times and mass spectral interpretations and were further supported by Raney Ni desulfurization of the "aromatic hydrocarbon" fractions which afforded a mixture of n-alkanes dominated by n-tritriacontane, n-heptatriacontane, and n-octatriacontane (Figure 2). This experiment established that the carbon skeletons of the high molecular weight OSC are mainly linear.
Chart 1 CmHzm1m c f i , , , Ia, m + n = 29, n = 6 Ib, m + n = 29, n = 5
Q,
CmHzm1
"'CnH2w1
CmHzmQcnH~n+l
IIa,m+n=32,n=16 IIb,m+n=32,n=15 IIc,m+n=33,n=16 IId, m + n = 33, n = 15
C m b mO C n H 2 n + r
IIIa, m + n = 28, n = 6 IIIb, m + n = 28, n = 5 IIIc, m + n = 28, n = 4 IIId, m + n = 32, n = 16 IIIe, m+ n = 32, n = 15 IIIf, m + n = 33, n = 16 IIIg, m + n = 33, n = 15
I V a , m + n = 2 9 ,n = 6 Nb, m+ n = 29, n = 5 IVc,m+n=33,n=16 IVd, m + n = 33, n = 15 IVe,m+n=34,n=17 IVf, m + n = 34, n = 16
CmHzm& " ' G 4 2 ~ 1
Va, m + n = 29, n = 6 Vb, m + n = 29, n = 5 Vc, m + n = 33, n = 16 Vd, m + n = 33, n = 15 Ve,m+n= 34,n=17 Vf, m + n = 34, n = 1 6
Mass Spectral Features of DATP, DATN, and DATL. The mass spectral features of DATP, DATN, and DATL have been discussed recently.15-17 The mass spectra of DATP are characterized by /3-cleavage of the alkyl side chains resulting in fragment ions x and y (Figure 3a). The relative intensities of these ions depend on the ratio of the lengths of the side chains; Le., the longer side chain is more feasible for cleavage due to the high stability of the alkyl radical formed; this results in a more intense B-fragmentation ion compris(15)Schmid, J. C. Ph.D. Thesis, University of Strasbourg, Strasbourg, 1986. (16) Sinninghe Damst6, J. P.; de Leeuw, J. W.; Kock-van Dalen, A. C.; de Zeeuw, M. A.; de lange, F.; Rijpstra, W. I. C.; Schenck, P. A. Geochim. Cosmochim. Acta 1987,51,2369-2391. (17)Payzant, J. P.; McIntyre, D. D.; Mojelsky, T. W.; Torres, M.; Montgomery, D.S.; Strausz, 0. P. Org. G'eochem. 1989,14, 461-473.
Energy &Fuels, Vol. 8, No. 6,1994 1171
Organic Sulfur Compounds in Sediment Extracts
13
Nordlinger Ries Well-10; Depth 250.0 m Saturated hydrocarbons after desulfurization
70
>
6o
.-5
50
Q, + C
40
E
3738
E
I
31
I
, I 80
70
60
90 Retention time, min
110
100
33
Nordlinger Ries Well-30; Depth 222.9 rn Saturated hydrocarbons after desulfurization
120
>
100
.-w
80
37
E
38
v)
C
s'
Q,
-C w
60 29
31
I
40
20 80
70
60
100
90 Retention time, min
110
Figure 2. Partial expanded capillary column gas chromatograms of the desulfurized aromatic hydrocarbon fractions of samples from the Nordlinger Ries. Arabic numbers indicate number of carbon atoms of n-alkanes,s' = 17/3(H),21/3(H)-pentakikishomohopane.
"eRi "&Rq
$R & 2:
a. b. C. Figure 3. Mass spectrometric fragmentation fc%hres
r
of
midchain cyclic sulfur compounds [after Sinninghe Damste et -1 /--r in11 LU. !LGl I U I J .
ing the shorter alkyl chain. When the length of the alkyl side chains exceeds Cs (ie., in midchain di-nalkylthiophenes), loss of both side chains by olefin elimination from the primary P-cleavage fragment becomes more important resulting in an intense ion at mlz 111. On the other hand, the mass spectra of DATN
and DATL are characterized by the fragmentations exemplified in Figure 3, b and c; a-cleavage of the alkyl side chains results in ions p and q. Again, the relative intensities of these ions depend on the ratio of the lengths of the alkyl side chains. If both alkyl side chains ,,nn+nin mnra
b Y I I Y U I I I
-
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u
thnn thrnn pslrh,-,n a t n m a Y L A U I I
"AAL
uu
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~e~nnAarx~ U"YA'uu-J
framentation as indicated for the thiophenes gain increasing importance leading to prominent ions at m l z 101and 87 for DATN and DATL, respectively. Cleavage through the thiane or thiolane ring accompanied by hydrogen transfer (fragmentation r, Figure 3b,c)results in an ion with an m l z value of 56 and 42 Da less than ion p (or q if the side chain is long enough), respectively. Furthermore, a displacement reaction, probably via a
Barakat and Rullkotter
1172 Energy &Fuels, Vol. 8, No. 6, 1994
11'
167
490
a. 181
97
I " ' " " ' '
100
200
500
400
300
600
mlz Figure 4. Mass spectrum and proposed structures of dominant components of peak a from Figure 1.
five-membered-ring transition state, gives rise to fragment t, which has an mlz value of 42 Da more than ion q (or p).16 OSC with a C33 Carbon Skeleton. Based on the previous discussion, the mass spectrum of peak a from Figure 1 is tentatively interpreted as a coeluting mixture of the DATP Ia and Ib (see structures in Table 1). It is characterized by a molecular ion at m l z 490, a base peak at m l z 111, and intense ions a t mlz 167,433 and 181,419 resulting from P-cleavage of the side chains (Figure 4). Substitution at the 2 and 5 positions is established by Raney Ni desulfurization which afforded only one isomer of tritriacontane having a linear carbon skeleton (see Figure 2). Two mass spectra of peak b (bl and b2 in Figure 61, corresponding to the top of the peak and to a comparatively weak shoulder, are shown in Figure 5. Based on the mass spectral features depicted in the latter figure, peak b is thought to represent a mixture of three C33 midchain DATN having structures IIIa-c in which compound IIIb is the dominant isomer. The mass spectra of peaks c and d (Figure 6) are also shown in Figure 5. Their mass spectra exhibit fragmentation patterns similar to each other; they are characterized by a molecular ion at m l z 494, and intense ions a t mlz 87, 157, 171, 409, and 423. The mass spectrum of peak d also shows a series of peaks between m l z 87 and 494 spaced apart by 14 Da. This complex mass spectrum corresponds t o an unresolved mixture of thiolane structural isomers in which the sulfur atom is located at various positions along the chain. The general resemblance of the mass spectra of peaks c and d suggests that, apart from the occurrence of the various positional isomers, the cis and trans isomers of virtually all positional isomers occur. By analogy,16the cis isomer is the first eluting isomer. This result is in agreement with previous studies16J7which indicated that gas chromatogram separations on a CPSi1 5 (equivalent to the GC columns used in this work) accomplishes a separation between these stereoisomers rather than between positional isomers. Moreover, the intense ions at m l z 157 and 171 reveal that each of the dominant cis and trans stereoisomeric midchain thiolanes occurs as two positional isomers tentatively identified as 2-hexyl-54ricosylthiolaneand 2-pentyl-5tetracosylthiolane.
200
100
300
500
400
199
423
0 100
-
E>
100 80
300
200
57
-
a?
l?l 157
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409 423
100 1
500
400
100
200
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200
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300
400
500
300
400
500
55
,
mlr
Figure 5. Mass spectra and proposed structuresof dominant components of peaks bl, bz, c, and d from Figure 6. OSC with Cs, and CSSCarbon Skeletons. Mass spectral analysis of the cluster of peaks labeled e-1 in Figure 1 reveals that they correspond to a complex mixture of midchain C37 and C38 cyclic sulfides (see identifications in Table 1). Midchain DATN are discriminated from the corresponding DATL by their chromatographic and mass spectral data (DATN elute earlier than DATL12), while recognition of the cis and trans stereoisomers is based solely on the relative retention times. Compound recognition and isomer distribution can be conveniently studied by monitoring the characteristic fragmentation ions m l z 87,101,550,
Energy & Fuels, Vol. 8, No. 6, 1994 1173
Organic Sulfur Compounds in Sediment Extracts
Nordlinger Ries Well-10 (250 m) Aromatic hydrocarbons
-
CaMIF C,OAIN
100 50 100
C,, OAIN
nd OAT1
c,
DAW
641504.
--
4v.
n d o ~ n mdom
TIC
mlz 564
50 100
mlz 550
50 100
I
mlz 87
33806.
50 -
1800
2000
2200
2400
Scan number Figure 6. Partial expanded mass fragmentograms (m/ z 87,101,550,564) and total ion current (TIC) of the aromatic hydrocarbon fraction of the Nordlinger Ries sediment sample obtained a t 250.0 m depth from Well-10.
and 564. The resulting fragmentograms for the sample from NR-10 (250.0m) are shown as an example in Figure 6. Peaks corresponding to the various C37 and c 3 8 thianes and thiolanes are indicated in this figure. In both samples, the C37 and c38 cyclic sulfides are dominated by midchain DATN rather than the corresponding DATL; this observation is more pronounced in the sample from 222.9 m depth in well NR-30 (Figure 1). Furthermore, the relative concentrations of the cis midchain DATN and DATL are lower than those of the corresponding trans compounds while the reverse was observed in the sample from NR-10 (250.0 m). The mass spectra of several of these peaks are presented in Figure 7. As shown, the mass spectra correspond to a n unresolved mixture of structural isomers in which the sulfur atom is located at various positions along the chain. They are, however, dominated by isomers with the sulfur atom located midway along the chain. Proposed structures of the dominant isomers are given in Table 1. Origin and Geochemical Significance. C33 midchain 2,5-di-n-alkylthiophenes(compounds Ia and Ib, Table 1)have been observed as major thiophenes in samples from offshore Morocco (ODP Site 547, Cretaceous black shales)18and in the Jurf ed Darawish oil shale (upper Cretaceous, Calcareous bituminous marl from Jordan).lg To our knowledge, C a midchain thianes and thiolanes have not been previously reported in sediments and petroleum. The origin of the C33 midchain cyclic sulfides is unknown. Composite mass spectra depicted in Figures 4 and 5 reveal that each class of the C33 midchain cyclic sulfides is dominated
Figure 7. Mass spectra and proposed structures of dominant components of peaks e, h, i, and 1 from Figure 6.
(18) ten Haven, H. L.; Rullkotter, J.; Sinninghe Damst.4, J. S.;de Leeuw, J. M., W. In Geochemistry of Sulfur in Fossil Fuels; Om,W. L., mite, c. ACS Series 42g; Society: Washington, DC, 1990; pp 613-632. (19) Kohnen, M. E. L.; Sinninghe Damst.6, J. S.;Rijpstra, W. I. C.; de Leeuw, J. W. In Geochemistryof Sulfur in Fossil Fuels; Om,W. L., Chemical mite,c. M.,Eds.; ACS Symposium Series 429; Society: Washington, DC, 1990; pp 444-485.
by the same specific structural isomers. This remarkable similarity between the structures of the positional isomers in the three classes of C33 OSC suggests a common genetic origin. Based on the proposed hypothetical model for the incorporationof sulfur into organic matter presented by Sinninghe Damst6 et al.,I2 tritria-
367 269 2m L
100
200
300
mlz
100
200
300
381 I 400
-.&-
400
500 an
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.-rE
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100,
200
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mlz
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1174 Energy & Fuels, Vol. 8, No. 6, 1994
conta-@-diene may be a suitable precursor for these C33 midchain monocyclic sulfur compounds. This lipid andor lated compounds have not been reported in either sediments or organisms but since long-chain polyunsaturated n-alkenes have been reported in algae (e.g., C34:3, C34:4,C35:5)22,23 C Z ~ , and ~ ) sediments ~ ~ J ~ (e.g., CZ~:Z, it seems not unreasonable to propose such a precursor. The C37 and c38 midchain DATN and DATL have been identified in Jurfed Darawish oil shale bitumen.12 It has been proposed that these C37 and c38 linear OSC are derived by incorporation of sulfur into C37 and c38 di- and triunsaturated methyl and ethyl ketones or their corresponding alkadienes and alkatrienes which are ubiquitous in sedimentsZ4J6and in the coccolithophorid Emilania h ~ x l e y i .It~ ~ is interesting t o note that the isomer clusters of the C37 and c38 midchain DATN and DATL identified in the Jurf ed Darawish bitumen were dominated by the same specific structural isomers found in the Nordlinger Ries samples (Table 1). The dominance of certain structural isomers cannot be explained by a reaction of elemental sulfur with saturated hydrocarbons. Further, the aliphatic hydrocarbon fractions of the Nordlinger Ries samples were dominated by n-alkanes which are deprived of n-C37 and n-C38 hydrocarbons. This observation substantiates previous suggestions12J6of the formation of OSC by early diagenetic sulfur incorporation into functionalized precursors. The results also reflect the usefulness of (20) Blumer, M.; Mullin, M. M.; Guillard, R. R. L. Mar. Biol. 1970, 6,226-235. (21) Lee, R. F.; heblich, A. R. Phytochem. 1971, 10,593-602. (22) Volkman, J. K.; Allen, D. I.; Stevenson, P. L.; Burton, H. R. In Advances in Organic Geochemistry, 1985; Leythaeuser, D., Rullkotter, J., Eds.; Org. Geochem. 1986, 10,671-681. (23) Boon. J. J.: van der Meer. F. W.: Schuvl. P. J.: de Leeuw. J. W.;, Schenck, P. A,;Burlingame,’A. L. Init. R>p. Deep Sea Drill& Project 1978, 40, 627-637. (24) de Leeuw, J. W.; van der Meer, F. W.; Rijpstra, W. I. C.; Schenck, P. A. In Advances i n Organic Geochemistry, 1979; Douglas, A. G., Maxwell, J. R., Eds.; Pergamon: Oxford, U.K., 1980; pp 211-
-.-
Zl I .
(25) Volkman, J. K.; Eglinton, G.; Corner, E. D. S.; Sargent, J. R. In Advances i n Organic Geochemistry, 1979; Douglas, E. G., Maxwell, J. R., Eds.; Pergamon: Oxford, U.K., 1980; pp 219-227. (26) Marlowe, I. T.; Brassel, S. C.; Eglinton, G.; Green, J. C. Org. Geochem. 1984, 6 , 135-141.
Barakat and Rullkotter OSC in providing geochemical information. Quenching of the original functionalized lipids with HzS has preserved early diagenetic information, i.e., the predominance of C37 and c38 n-alkanes reminiscent of longchain unsaturated ketones from Prymnesiophytae algae, which is no longer available from the saturated hydrocarbon fraction. A similar effect had been noted before for crude oils from the Monterey Formation (California) where abundant C37 and c38 n-alkanes were released from the “aromatic hydrocarbon”fractions while the free saturated hydrocarbons did not show any particular dominance of n-alkanes with these carbon numbemZ7 Considering the long chain unsaturated ketones as precursors of midchain, the C37 and c38 DATN and DATL in Nordlinger Ries black shales also means that reaction with sulfur specifically occurred with the double bond functionalities of the long-chain alkenones of Prymnesiophyte origin because corresponding terminal DATN and DATL formed by reaction with the 2- or 3-keto group could not be detected. This is further substantiated by the observation that a homologous series of 2-thiols in Nordlinger Ries bitumens likely to be derived from interaction of alkan-2-ones with inorganic sulfur species during early diagenesis does not comprise C37 and c38 members.28
Acknowledgment. We are grateful to BEB Erdgas und Erdol GmbH (Hannover) for providing the Nordlinger Ries samples and for permission to publish the results. A.O.B. is grateful to the Alexander von Humboldt Foundation for a research grant and for donating the GCMS processing unit t o Alexandria University. This work was begun a t the Institute of Petroleum and Organic Geochemistry, KFA, Julich, FRG, and was completed at the Department of Chemistry, Alexandria University. Liquid and gas chromatography were supervised at KFA Julich by Dr. M. Radke and Dr. R. G. Schaefer, respectively. Technical assistance was provided by A. Fischer, U. Disko, R. Harms, and F. J. Keller. (27) Rullkotter, J.;Michaelis, W. Org. Geochem. 1990,16,829-852. (28) Barakat, A. 0.;Rullkotter, J. Unpublished results.
