ISSN 0965�5441, Petroleum Chemistry, 2012, Vol. 52, No. 3, pp. 213–214. © Pleiades Publishing, Ltd., 2012.Original Russian Text © E.V. Rakhmanov, Wang Zixiao, A.V. Tarakanova, M.S. Oshchepkov, A.V. Anisimov, 2012, published in Neftekhimiya, 2012, Vol. 52, No. 3, pp. 239–240.

213

Ionic liquids (ILs) hold much promise as a reactionmedium regarding the current methods for oxidationof organic sulfur compounds. The set of properties ofthese liquids, such as high polarity, thermal stability,low melting point, hydrophobicity, and low solubilityin organic solvents, make them attractive for conduct�ing various organic reactions including the oxidationof organic sulfur compounds [1–3].

In this work, ionic liquids of different structureswere used as a medium for oxidation of diben�zothiophene with hydrogen peroxide. Diben�zothiophene is one of hardly oxidizable organic sulfurcompounds present in high�boiling�point petroleumcuts, in particular, diesel fuel [4]. Thus, searching foroxidant systems that ensuring a high degree of oxida�tive conversion of this and analogous compounds is ofspecial importance.

EXPERIMENTAL

Reactants and analysis for products. Diben�zothiophene and NbCl5 were obtained from Aldrich,hydrogen peroxide (37% aqueous solution) wasobtained from a commercial source, ionic liquids 1–6were supplied by Merck, and azacrowns were synthe�

sized as described in [6]. The purity of the reactantswas monitored and the product composition wasdetermined by GLC on a Kristall�2000M chromato�graph with a flame�ionization detector and a Zebroncolumn (l = 30 m, d = 0.32 mm); the liquid phase wasZB�1 and the temperature was programmed from 100to 230°С.

Oxidation of dibenzothiophene in the presence ofILs. A 0.25�g portion of IL was added to 5 g of a modelmixture that was composed of 1% dibenzothiophenein hexadecane. The reaction mixture was heated to40°С, 0.02 mL of 37% hydrogen peroxide aqueoussolution was added with stirring, and stirring contin�ued for 8 h at this temperature. After cessation of stir�ring and heating, 5 mL of water and 1 g of sodium thio�sulfate were added to the resulting mixture. Theorganic phase was separated from the aqueous phase ina separating funnel, dried over anhydrous calciumchloride, and analyzed by GLC

RESULTS AND DISCUSSION

The following ionic liquids (1–6) having differentstructures with varying both the cation and the anionwere used as a medium for oxidation reactions:

NBuH3C

N

N

CH3

Bu

N

N

CH3

Bu

N

N

CH3

Bu

N

CH3

Bu

Ph3P (CH2)4 SO3H TsO–

PF–+ +

+

6

BF–4

N(SO2CF3)–2+

P(C2F5)3F–3 PF–

6+

+

1 2 3

4 5 6

Oxidation of Dibenzothiophene with Hydrogen Peroxidein Ionic Liquids

E. V. Rakhmanov, Wang Zixiao, A. V. Tarakanova, M. S. Oshchepkov, and A. V. AnisimovFaculty of Chemistry, Moscow State University, Moscow, 199991 Russia

e�mail: anis@petrol.chem.msu.ruReceived November 8, 2011

Abstract—Structurally different ionic liquids have been used as a medium for oxidation of dibenzothiophenewith hydrogen peroxide in the presence of niobium pentachloride and oxaazacrown ethers. The maximumdegree of oxidative conversion of dibenzothiophene (63%) was achieved in the presence of 5�(1,4,7,10�tet�raoxa�13�azacyclopentadecan�13�yl)pentadecanoic acid, an oxaazacrown ether bearing the carboxylicgroup in a side chain.

DOI: 10.1134/S0965544112030103

214

PETROLEUM CHEMISTRY Vol. 52 No. 3 2012

RAKHMANOV et al.

The oxidant was a 37% hydrogen peroxide aqueoussolution, and auxiliary substances were niobium pen�tachloride NbCl5 and azacrowns of different struc�tures.

As follows from the obtained data, the oxidation ofdibenzothiophene taken as a 1% solution in n�hexade�cane results in the formation of dibenzothiophene sul�fone. Note that the IL structure has a slight effect onthe oxidation: variation of the cation or anion struc�ture leads to dibenzothiophene oxidative conversionnot more than by 22%; the addition of niobium pen�tachloride to the reaction mixture also doe not lead toa significant improvement in characteristics of the oxi�dation reaction (Table 1).

The maximum degree of dibenzothiophene oxida�tive conversion to dibenzothiophene sulfone wasachieved in IL�5 with the P(C2F5)3F

– anion to be aslow as 22%.

A considerable improvement in the characteristicsof dibenzothiophene oxidation was achieved whenazacrowns were added as a catalyst, which are capableof effective complexation with metal cations andhydrogen peroxide [5].

The above data show that running the reaction inthe presence of an azacrown alone without IL does notresults in a significant rise in the degree of oxidativeconversion of dibenzothiophene. If the process is car�ried out in the presence of IL with an admixture of theether which contains the carboxylic group in the sub�

stituent on the macrocycle as in [5�(1,4,7,10�tet�raoxa�13�azacyclopentadecane�13�yl)pentadecanoicacid], the maximum degree of dibenzothiophene oxi�dative conversion increases to 63%.

The obtained results show that the effective oxida�tion of hardly oxidizable dibenzothiophene withhydrogen peroxide in an IL medium hold the bestpromise in the presence of azacrowns with the carbox�ylic functional group on the periphery of a substituentattached to the macrocycle.

ACKNOWLEDGMENTS

This work was supported under the 2009–2013Federal Target Program “Scientific�Research andAcademic Personnel for Innovative Russia”, (programitem 1.2.2.

REFERENCES

1. J. Dupont, R. F. de Souza, and P. A. Z. Suarez, Chem.Rev. 102, 3667 (2002).

2. W. Zhu, W. Huang, H. Li. M. Zhang, et al., Fuel Pro�cess. Technol. 92, 1842 (2011).

3. T. Rajkumar and G. R. Rao, Mater. Chem. Phys. 112,853 (2008).

4. L. Kong, G. Li. X. Wang, and B. Wu, Energy Fuel 20,896 (2006).

5. E. V. Rakhmanov, Dan Jinyuan’ O.A. Fedorova, et al.,Pet. Chem. 51, 216 (2011).

6. M. S. Oshchepkov, V. P. Perevalov, L. G. Kuz’mina,et al., Izv. Akad. Nauk, Ser. Khim., No. 3, 468 (2011).

Table 1. Oxidation of dibenzothiophene with hydrogenperoxide in the presence of various ionic liquids (40°C, 8 h,S(total sulfur) : H2O2 : NbCl5 molar ratio = 100 : 240 : 1)

Ionic liquidDegree of oxidation of dibenzothiophene,%

without NbCl5 with NbCl5

IL�1 0 0

IL�2 12 21

IL�3 12 20

IL�4 11 8

IL�5 22 22

IL�6 19 14

Table 2. Oxidation of dibenzothiophene in the presence ofIL�6 and azacrowns ethers (40°C, 8 h, S(total sulfur) : H2O2molar ratio = 1 : 2.4)

IL and azacrown Degree of oxidation of dibenzothiophene, %

Without IL, 1�aza�15�crown�5 19

IL�6, 1�aza�15�crown�5 61

IL�6, 5�(1,4,7,10�tetraoxa�13�azacyclopentadecane�13�yl)pen�tanoic acid

63