ALKYLATED 2,2'-BITHIOPHENES AND 2-PHENYLTHIOPHENES
187
drawal arm placed in a trap (5 ml of chloroform at 0°ë). (methyl- and butyl-substituted derivatives) were syn-
The pyrolysis was carried out in a nitrogen stream for thesized for each homologous series. The presence of
1 h at 420°ë [6]. The pyrolysis products were concen- two members of the homologous series allows the
trated in preliminarily weighed weighing bottles (frac- group identification of members of this series to be per-
tion P0).
formed on the basis of the dependence of the retention
time on the number of carbon atoms in a homologue
molecule [7].
The pyrolyzate P0 was divided into two fractions by
liquid chromatography on a column (10 × 1.5 cm)
packed with alumina (Fluka), which was preliminarily
activated for 2.5 h at 150°ë. Elution with an n-hexane–
dichloromethane (9 : 1, vol/vol) mixture gave an apolar
fraction (P1) containing all aliphatic and aromatic com-
ponents of P0. With a dichloromethane–ethanol (1 : 1)
blend used as an eluent, polar components (P2) were
eluted. Then, P1 was separated into the aliphatic (P3)
and aromatic (P4) fractions. For this purpose, a column
(8 × 0.6 cm) packed with silica gel (Fluka) was used.
Fraction P3 was obtained via elution with n-hexane,
and elution with benzene gave fraction P4.
The analysis by gas chromatography coupled with
mass spectrometry (GC–MS) was performed on a QP
5050A instrument (Shimadzu). An SPB-5 column
(Supelco) of 60 m length and 0.32 mm inner diameter
was used for chromatographic separation (the station-
ary-phase layer thickness was 0.25 µm). Chromatogra-
phy was carried out in the temperature-programming
mode from 50 to 300°ë at a rate of 5°ë /min. The injec-
tor temperature was 300°ë, and the temperature of the
ion source was 250°ë. A sample was injected in the
flow-splitting mode (1 : 30), and the sample volume
was 1 µl. A quadrupole mass spectrometer with an ion-
ization energy of 70 eV was used.
A sample of oil shale KSh-1/5-03 taken from the
Kashpirskoe deposit was chosen as a source of high-
sulfur kerogen: the organic carbon content was 37.3%
and the amount of chloroform-extractable bitumens
was 0.36%. The analysis of the unfractionated pyrolyz-
ate of this kerogen showed the presence of low-molec-
ular-mass thiophenes in high concentrations. For exam-
ple, the thiophene ratio (TR is the ratio of the 2,3-dim-
ethylthiophene content to the sum of 1-nonene and
1,2-dimethylbenzene) used for estimating Sorg in the
kerogen composition is 0.81, which corresponds to an
S/C value of 0.05 [8]. The elemental analysis data allow
us to attribute this kerogen to the type II-S (H/C = 1.52,
S/C = 0.053). According to Orr’s classification [9],
geopolymer samples with an S/C atomic ratio above
0.04 and H/C atomic ratios characteristic of type II ker-
ogen are categorized with type II-S kerogen.
The analysis of the aromatic fraction of the pyroly-
sis products of Kashpirskii kerogen showed the pres-
ence of a wide variety of sulfur-containing compounds.
To reveal bithiophene and phenylthiophene derivatives
in the composition of the P4 fraction, we constructed
mass fragmentograms by the following m/z sums:
179 + 180 for 5-n-alkyl-2,2'-bithiophenes, 193 + 194
for 5-n-alkyl-5'-methyl-2,2'-bithiophenes, 173 + 174
for 2-n-alkyl-5-phenylthiophenes, and 187 + 188 for
and 2-n-alkyl-5-o-tolylthiophenes (Fig. 1). The P4 frac-
tion with added authentic standards was chromato-
graphed to confirm the presence of these compounds in
the kerogen pyrolysis products (Fig. 2). The heights of
the corresponding peaks increased, thus confirming the
validity of the identification. Taking into account that
we synthesized two members for each of the test
homologous series, the retention times of the interme-
diate members of the homologous series were deter-
mined by the interpolation method.
Proton NMR spectra were recorded on a Bruker
instrument at a frequency of 300 MHz in CDCl3. The
chemical shifts were measured relative to tetramethyl-
silane.
RESULTS AND DISCUSSION
We synthesized eight compounds belonging to the
2,2'-bithiophene and 2-phenylthiophene series. The
structures of these compounds were confirmed by syn-
thesis and the mass spectral and 1H NMR data (table).
The main pathway of the mass-spectrometric degrada-
tion of alkylated aromatic compounds, including
thiophenes, is the β-cleavage of the alkyl chain [7]. In
the case of methyl-substituted derivatives, the molecu-
lar and M-1 ions have the highest abundance. This spe-
cific feature of the mass-spectral decomposition is
employed for the group identification of bithiophenes
and phenylthiophenes in the pyrolysis products of ker-
ogen by means of the GC–MS technique [1].
The kerogen represented a geopolymer of an irregu-
lar structure containing the n-alkyl, isoprenoid, and
polycyclic, aromatic, and heteroatomic moieties
bridged to one other by different linkages: ester, ether,
sulfide, and polysulfide bridges [10]. Type II kerogen is
characterized by a higher Sorg content, in which organic
sulfur appears in heterocycles and forms bridges
between its local carbonaceous structures, thus deter-
The synthesized compounds belong to four homol- mining the special properties of sulfur-rich kerogen
ogous series, namely, 5-n-alkyl-2,2'-bithiophenes, 5-n- [11]. Sulfur is inserted into the kerogen at the diagene-
alkyl-5'-methyl-2,2'-bithiophenes,
5-n-alkyl-2-phe- sis stage as a result of the interaction of functionally
nylthiophenes, and 5-n-alkyl-2-o-tolylthiophenes. Two saturated lipids of the original organic matter with
compounds that differ by three methylene units reduced forms of sulfur [4]. In addition, under certain
PETROLEUM CHEMISTRY Vol. 47 No. 3 2007