Desulfurization of dibenzothiophene and oxidized dibenzothiophene ring systems

Article abstract of DOI:10.3390/molecules15031265

Lithium, used in conjunction with sodium metal, produces a high yield of biphenyl when reacted with dibenzothiophene, dibenzothiophene sulfoxide or dibenzothiophene sulfone.

Full text of DOI:10.3390/molecules15031265

Molecules 2010, 15, 1265-1269; doi:10.3390/molecules15031265
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Desulfurization of Dibenzothiophene and Oxidized
Dibenzothiophene Ring Systems
Diego P. Morales, Alexander S. Taylor and Steven C. Farmer *
Department of Chemistry, Sonoma State University, 1801 East Cotati Avenue, Rohnert Park,
CA 94928, USA
∗ Author to whom correspondence should be addressed; E-Mail: farmers@sonoma.edu;
Tel.: +1-707-664-3728.
Received: 1 February 2010; in revised form: 24 February 2010 / Accepted: 2 March 2010 /
Published: 3 March 2010
Abstract: Lithium, used in conjunction with sodium metal, produces a high yield of
biphenyl when reacted with dibenzothiophene, dibenzothiophene sulfoxide or
dibenzothiophene sulfone.
Keywords: dibenzothiophene; desulfurization; sulfoxides; sulfones
1. Introduction
The reductive desulfurizations of various types of organosulfur compounds are of importance in
industry, mainly because of their application in the desulfurization of fossil fuels to reduce pollution
[1,2]. The desulfurization of polycyclic aromatic sulfur compounds such as benzo- and
dibenzothiophenes are of particular interest because of their widespread occurrence in fossil fuels.
The desulfurization of polycyclic aromatic sulfur compounds also has applications in the laboratory
[3–5]. Because the sulfur atom in such heterocycles has a strong directing effect towards electrophillic
aromatic substitution reactions, the subsequent desulfurization could provide a regioselective entry to
substituted biphenyls and related compounds. Because of this and the fact that dibenzothiophenes are
particularly difficult to desulfurize by conventional methods, new methodology that can efficiently
perform this reaction are of great interest. Examination of the literature dealing with the
desulfurization of dibenzothiophene shows that numerous synthetic problems remain unsolved and that
room for new reagents exists. Some examples of the desulfurization of dibenzothiophene (1) to make

Molecules 2010, 15
1266
biphenyl (2) have been reported, however these reactions involve long reaction times [6,7], high
temperatures [8–10], complex reagents [11] or low yields [16]. In addition there have been very few
examples of the desulfurization of dibenzothiophene sulfoxide (3) [17,18], and dibenzothiophene
sulfone (4) [10,19–21] as S-oxidized derivatives of this ring system. In fact, both lithium and sodium
[10] have been used to effect sulfur extrusions from dibenzothiophene. However, in both cases low
yields occurred unless high temperatures were used. The high temperatures required that the high
boiling point solvent, tetradecane, be used. The removal of high boiling point solvents from reaction
mixtures can be difficult. The generation of a method which can afford high sulfur extrusion yields,
while still using a solvent which can be removed by rotary evaporation, would be of great benefit. In
this manuscript we apply our previous work using lithium in combination with sodium as an efficient
method for the desulfurization of heterocycles [22,23].
2. Results and Discussion
In the past we have increased the sulfur extrusion ability of lithium by using it in conjunction with
sodium. By combining these two metals we were able to utilize the increased reducing ability of
sodium while still maintaining the sulfur removing effects of lithium. Also, the synergistic effect of
using both metals together allowed for the reaction temperature to be reduced such that refluxing
dioxane could be used. This solvent was easily removed by rotary evaporation during the reaction
work-up. The use of sodium in conjunction with lithium increased the yield of biphenyl from
dibenzothiophene to 88% (Scheme 1). Owing to the dianion intermediate mechanism proposed by
Gilman [16] it was decided that the sulfoxide and sulfone derivatives of dibenzothiophene could
stabilize the intermediates of this reaction; thereby, increasing the biphenyl yield (Scheme 2). This
turned out to be the case with dibenzothiophene sulfoxide, which produced a biphenyl yield of 90%.
Dibenzothiophene sulfone also produced an increased biphenyl yield (96%). In all cases the reactions
produced no side products. Occasionally, some starting material would be isolated.
Scheme 1. The desulfurization of dibenzothiophene (1).
Li & Na
Dioxane
Reflux
-M2S
S
(1)
(2)
Scheme 2. The desulfurization of dibenzothiophene sulfoxide (3) and sulfone (4).
Li & Na
Dioxane
Reflux
-M2R
R
O
S
R =
R =
(3)
(2)
O
O
(4)
S

Molecules 2010, 15
1267
3. Experimental
3.1. General
All infrared spectra were recorded on a Perkin Elmer Spectrum 1000 FTIR infrared spectrometer
1
and were performed neat on a NaCl plate. H-NMR were obtained on a General Electric QE-300 at
13
300 MHz in CDCl3 using TMS as the reference. C-NMR were obtained at 75 MHz in CDCl3. All
GCMS spectra were recorded using a Shimadzu GCMS-QP500 gas chromatography/mass
spectrometer. All melting points are uncorrected and were measured using a Mel Temp 3.0 melting
point apparatus. Chromatography was accomplished using 20 to 230 mesh silica gel. Thin layer
chromatography was performed using plastic backed silicagel 60 F254 plates. Unless otherwise stated,
all reagents were obtained from commercial sources and were used without further purification. The
compound dibenzothiophene sulfoxide (3) was made using a literature method [24].
3.2. Biphenyl (2) from dibenzothiophene (1) using Li/Na
In a 25 mL round-bottomed flask dibenzothiophene (0.150 g, 0.814 mmol) was dissolved in
dioxane (10 mL). To this was added lithium dispersion (0.050 g, 7.20 mmol) in mineral oil and sodium
metal (0.200 g, 8.70 mmol). The mixture was heated at reflux for 12 h, after which time any remaining
lithium or sodium was destroyed with careful addition of methanol. The organic solvent was removed
by evaporation and the residue was dissolved in water (20 mL) and ethyl acetate (20 mL). The layers
were separated and the aqueous layer was extracted two more times with ethyl acetate (20 mL). The
combined organic layers were dried with sodium sulfate, filtered, and evaporated to produce a white
powder. Purification consisted of silica column chromatography, using hexane as the elution solvent.
After work-up the reaction produced 0.110 g (0.713 mmol) of pure biphenyl, a yield of 88%. m.p.
68.4–69.1 ºC (lit. m.p. 68–69 ºC [25]); IR (cm−1, Neat): 3,033 (w, Ar-H), 1,482 (w, C=C), 1,430 (w,
1
C=C); H-NMR: δ (ppm) 7.58 (d, J = 7.5 Hz, 4H), 7.42 (t, J = 7.5 Hz, 4H), 7.33 (t, J = 7.5 Hz, 2H);
13C-NMR: δ (ppm) 141.21, 128.73, 127.23, 127.15 [25]; MS (EI, m/z) 154 (M+).
3.3. Biphenyl (2) from dibenzothiophene sulfoxide (3) using Li/Na
The same general procedure was followed as above except sodium metal (90.0 mg, 3.91 mmol) and
lithium dispersion (60.0 mg, 8.64 mmol) was reacted with dibenzothiophene sulfoxide (0.100 g,
0.499 mmol). The reaction was refluxed for 24 h. The reaction produced 69.2 mg (0.449 mmol) of
pure biphenyl, a yield of 90%. m.p. 69.3–71.7 ºC; IR, NMR and MS, identical in all respects to an
authentic sample.
3.4. Biphenyl (2) from dibenzothiophene sulfone (4) using Li/Na
The same general procedure was followed as above except sodium metal (0.100 g, 4.35 mmol) and
lithium dispersion (60.0 mg, 8.64 mmol) was reacted with dibenzothiophene sulfone (0.100 g,
0.462 mmol). The reaction was refluxed for 24 h. The reaction produced 68.3 mg (0.443 mmol) of
pure biphenyl, a yield of 96%. m.p. 69.3–70.5 ºC; IR, NMR and MS, identical in all respects to an
authentic sample.

Molecules 2010, 15
1268
4. Conclusions
By providing an efficient, high yield method for the desulfurization of dibenzothiophene and S-
oxidized dibenzothiophene ring systems, we have opened more possible synthesis routes for biphenyl
derivatives. These improvements may now be applied to other types of compounds that contain the
thiophene ring system.
Acknowledgements
We thank the Sonoma State University School of Science and Technology Summer High School
Internship Program for supporting this project. This project was also funded by the California State
University Louis Stokes Alliance for Minority Participation (CSU-LSAMP) Program.
References and Notes
1. Alper, H.; Blais, C. Removal of sulfur from fuels by molybdenum hexacarbonyl on silica. Fuel
1980, 59, 670.
2. El-Ansary, A.I.; Ezz, S.Y. Desulfurization of petroleum coke by butagas. Fuel 1973, 52, 66–70.
3. Arce, A.J.; De Sanctis, Y.; Karam, A.; Deeming, A.J. Desulfurization of benzo[b]thiophene by
S/Ru exchange: formation and structure of cluster [Ru3(CO)8(C8H6)]. Angew. Chem. Int. Ed. Engl.
1994, 33, 1381–1383.
4. Becker, S.; Fort, Y.; Caubere, P. New desulfurizations by nickel-containing complex reducing
agents. J. Org. Chem. 1990, 55, 6194–6198.
5. Ignasiak, T.; Kemp-Jones, V.; Strausz, O.P. The molecular structure of Athabasca asphaltene.
Cleavage of the carbon-sulfur bonds by radical ion electron transfer reactions. J. Org. Chem.
1977, 42, 312–320.
6. Torres-Nieto, J.; Arevalo, A.; Garcia, J.J. Catalytic Desulfurization of Dibenzothiophene and Its
Hindered Analogues with Nickel and Platinum Compounds. Organometallics 2007, 2,
2228–2233.
7. Chehata, A.; Oviedo, A.; Arevalo, A.; Bernes, S.; Garcia, J.J. Reactivity of [Ru3(CO)12] with
Dibenzothiophene, Methylbenzothiophene, and Methyldibenzothiophene. Organometallics 2003,
22, 1585–1587.
8. Berhault, G.; Perez De la Rosa, M.; Mehta, A.; Yacaman, M.; Chianelli, R.R. The single-layered
morphology of supported MoS2-based catalysts-The role of the cobalt promoter and its effects in
the hydrodesulfurization of dibenzothiophene. Appl. Catal. A: Gene. 2008, 345, 80–88.
9. Yang, S.; Prins, R. New synthesis method for nickel phosphide hydrotreating catalysts. Chem.
Commun. 2005, 33, 4178–4180.
10. Verkade, J.G.; Yu, Z. Desulfurization of organosulfur compounds with lithium and sodium Energ.
Fuel 1999, 13, 23–28.
11. Dye, J.L.; Cram, K.D.; Urbin, S.A.; Redko, M.Y.; Jackson, J.E.; Lefenfeld, M. Alkali Metals Plus
Silica Gel: Powerful Reducing Agents and Convenient Hydrogen Sources. J. Am. Chem. Soc.
2005, 127, 9338–9339.

Molecules 2010, 15
1269
12. Ishihara, A.; Nomura, M.; Kabe, T. Hydrodesulfurization of dibenzothiophene catalyzed by
alumina-supported ruthenium carbonyl-alkali metal hydroxide systems. Chem. Lett. 1992, 12,
2285–2288.
13. Nagai, M.; Urimoto, H.; Uetake, K.; Sakikawa, N.; Gonzalez, R.D. The desulfurization of
polynuclear aromatic sulfur compounds with a Raney nickel. Bull. Chem. Soc. Jpn. 1989, 62,
557–562.
14. Becker, S.; Fort, Y.; Vanderesse, R.; Caubere, P. Activation of reducing agents. Sodium hydride
containing complex reducing agents. NiCRA's and NiCRAL's as new efficient desulfurizing
reagents. J. Org. Chem. 1989, 54, 4848–4853.
15. Eisch, J.J.; Hallenbeck, L.E.; Han, K. Organic chemistry of subvalent transition metal complexes.
12. Hydrodesulfurization of organosulfur heterocycles by metal hydride-nickel(0) complexes:
accelerated single-electron transfer in carbon-sulfur bond cleavage. J. Am. Chem. Soc. 1986, 108,
7763–7767.
16. Gilman, H.; Esmay, D.L. The cleavage of heterocycles with Raney nickel and with lithium. J. Am.
Chem. Soc. 1953, 75, 2947–2949.
17. Back, T.G.; Yang, K.; Krouse, H.R. Desulfurization of benzo- and dibenzothiophenes with nickel
boride. J. Org. Chem. 1992, 57, 1986–1990.
18. Becker, S.; Fort, Y.; Caubere, P. New desulfurizations by nickel-containing complex
reducing agents. J. Org. Chem. 1990, 55, 6194–6198.
19. Kuehm-Caubere, C.; Guilmart, A.; Adach-Becker, S.; Fort, Y.; Caubere, P. Dramatic acceleration
of the desulfurization, with Ni containing complex reducing agents (NiCRA's). Tetrahedron Lett.
1998, 39, 8987–8990.
20. Becker, S.; Fort, Y.; Vanderesse, R.; Caubere, P. Activation of reducing agents. Sodium hydride-
containing complex reducing agents. 26. New efficient desulfurizing nickel-containing reagents.
Tetrahedron Lett. 1988, 29, 2963–2966.
21. Chan, M.C.; Cheng, K.M.; Ho, K.M.; Ng, C.; Yam, T.; Wang, B.S.L.; Luh, T. Transition-metal-
promoted reactions. 19. Nickelocene-lithium aluminum hydride: a versatile desulfurization
reagent. J. Org. Chem. 1988, 53, 4466–4471.
22. Miller, R.B.; Farmer, S.C. Modified methods for the synthesis of carbazole from phenothiazine.
Molecules 2001, 6, 668–672.
23. Farmer, Steven C.; Berg, Seth H. Ring contracting sulfur extrusion from oxidized phenothiazine
ring systems. Molecules 2008, 13, 1345–1352.
24. Gilman, H.; Dietrich, J.J. Lithium Cleavages of Some Heterocycles in Tetrahydrofuran. J. Am.
Chem. Soc. 1958, 80, 380–383.
25. Nising, C.F.; Schmid, U.K.; Nieger, M.; Bräse, S. A New Protocol for the One-Pot Synthesis of
Symmetrical Biaryls. J. Org. Chem. 2004, 69, 6830–6833.
Sample Availability: Samples are not available.
© 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
This article is an open-access article distributed under the terms and conditions of the Creative
Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).