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Organic Geochemistry 31 (2000) 523±534
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Geosynthesis of organic compounds.
Part V Ð methylation of alkylnaphthalenes
Trevor P. Bastow *, Robert Alexander, Steven J. Fisher, Raj K. Singh,
Ben G.K. van Aarssen, Robert I. Kagi
Australian Petroleum CRC/Centre for Petroleum and Environmental Organic Geochemistry, Curtin University, GPO Box U1987, Perth,
WA 6845, Australia
Received 24 August 1999; accepted 6 March 2000
(returned to author for revision 29 November 1999)

Abstract
Several crude oils and rock extracts with high concentrations of 1,6-dimethylnaphthalene, 1,2,5-trimethylnaphthalene, 1,2,3,5-tetramethylnaphthalene, 1,2,3,5,6-pentamethylnaphthalene and 6-isopropyl-2-methyl-1-(4-methylpentyl)naphthalene are also shown to contain enhanced distributions of their corresponding methylated counterparts. Of
these methylated counterparts, 1,2,3,5,6,7-hexamethylnaphthalene has been synthesised and is identi®ed in sedimentary
material for the ®rst time. In laboratory experiments carried out under mild conditions with a methyl donor in the
presence of a clay catalyst, each of the parent alkylnaphthalenes was shown to be substituted in preferential positions.
The distributions of these products from laboratory methylation experiments are similar to the distributions found in
sedimentary material. These observations have been interpreted as evidence for a sedimentary electrophilic aromatic
methylation process. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Methylation; Alkylation; Geosynthesis; Alkylnaphthalenes; Clay catalysis; Electrophilic aromatic substitution; 1,2,3,5,6,7Hexamethylnaphthalene

1. Introduction
Sedimentary methylation processes have been proposed
to account for the occurrence of numerous methyl substituted aromatic hydrocarbons with carbon skeletons
that are not obviously derived from common natural
product precursors (Radke et al., 1982a). The formation
of alkylaromatics by alkylation processes has been
demonstrated for alkylphenols (Ioppolo-Armanios et
al., 1995), benzenes (Ellis et al., 1995; He et al., 1995),
naphthalenes (He et al., 1992, 1994; Bastow et al., 1996),
phenanthrenes (Smith et al., 1994, 1995; Alexander et
al., 1995), anthracenes (Smith et al., 1994, 1995) and
pyrene (Derbyshire and Whitehurst, 1981; Smith et al.,

* Corresponding author. Tel.: +61-8-9266-3819; fax; +618-9266-2300.
E-mail address: t.bastow@info.curtin.edu.au (T.P. Bastow).

1994, 1995). Further evidence to support an alkylation
process comes from the identi®cation of 6-isopropyl-2,4dimethyl-1-(4-methylpentyl)naphthalene (4-Me-iP-iHMN)
as a methylation product of 6-isopropyl-2-methyl-1-(4methylpentyl)naphthalene (iP-iHMN) (Ellis, 1994; Ellis

et al., 1996; Bastow et al., 1999). In this paper we show
evidence for the formation of methylated alkylnaphthalenes via sedimentary methylation processes.
Dimethylnaphthalenes (DMNs), trimethylnaphthalenes
(TMNs), tetramethylnaphthalenes (TeMNs) and pentamethylnaphthalenes (PMNs) are common constituents
of petroleum and fossil fuels. The presence of abundant
1,6-DMN (Radke et al., 1990, 1994; van Aarssen et al.,
1992), 1,2,5-TMN (PuÈttmann and Villar, 1987; Strachan
et al., 1988; Killops, 1991; Ellis et al., 1996), 1,2,7-TMN
(Strachan et al., 1988; Forster et al., 1989), 1,2,5,6-TeMN
(PuÈttmann and Villar, 1987; Killops, 1991; Ellis et al.,
1996), 1,2,3,5-TeMN (Alexander et al., 1992, 1993),
1,2,3,5,6-PMN (Bastow et al., 1998) and iP-iHMN (Ellis,
1994; Ellis et al., 1996; Bastow et al., 1999) in low

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T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

1,2,3,5,6,7-Hexamethylnaphthalene (1,2,3,5,6,7-HMN)
was prepared using the synthetic scheme reported by
Araki and Mukaiyama (1974). 1,2,3-Trimethylbenzene
(13 mmol) in glacial acetic acid (50 ml) at 0 C, was
treated with bromine (15 mmol), and the mixture was
allowed to warm to room temperature over a period of 1 h
yielding 1-bromo-2,3,4-trimethylbenzene. The Grignard
reagent prepared from 1-bromo-2,3,4-trimethylbenzene
(8 mmol) and magnesium (5 mmol) was added to 2,3dimethylsuccinic anhydride (4 mmol) in tetrahydrofuran
(THF). The resulting keto carboxylic acid (2 mmol) was
reduced using zinc amalgam (Martin, 1942) to give the
carboxylic acid. The carboxylic acid (1 mmol) was
cyclised to 2,3,5,6,7-pentamethyltetralone by treatment
with polyphosphoric acid (PPA). The tetralone (0.5
mmol) was methylated using methylmagnesium iodide
and the resultant tertiary alcohol (0.4 mmol) was converted to the alkyltetralin by dehydration in a mixture
of sulfuric acid and glacial acetic acid. This alkyltetralin
was then treated with activated platinum (5%) on carbon
at 280 C to yield 1,2,3,5,6,7-HMN as a white solid (m.p.

172±174 C) with an overall yield of 8%. The 1H-NMR
spectra and melting point of this compound corresponded well with those reported by Chen et al. (1973)
(m.p. 173±174 C; 1H-NMR (CDCl3): d 2.34, s, 6H,
Ar(C2, C6)-CH3; 2.44, s, 6H, Ar(C3, C7)-CH3; 2.57, s,
6H, Ar(C1, C5)-CH3; 7.64, s, 2H, Ar(C4, C8)-H).

maturity sedimentary organic matter has led to the suggestion that these compounds originate from terpenoids
derived from microbial and land plant sources. However,
with increasing maturity the relative abundances of
these isomers are diminished until at high maturity the
isomer distributions re¯ect their relative stabilities
(Alexander et al., 1985, 1986, 1993; Strachan et al.,
1988; van Duin et al., 1997; van Aarssen et al., 1999).
This change in the relative abundances of isomers with
increasing maturity has been attributed to ring isomerisation and transalkylation processes (Strachan et al.,
1988; Alexander et al., 1993; Bastow et al., 1998; van
Aarssen et al., 1999). A recent study by van Aarssen et
al. (1999) has suggested that the distributions of TMNs,
TeMNs and PMNs are closely related as a result of isomerisation and transalkylation reactions and it has been
proposed that the methyl groups involved in these reactions

form a `methyl pool' to which every compound in a
crude oil has access.
In this paper we show that crude oils and rock
extracts with a high relative abundance in alkylnaphthalenes likely to be derived from natural product
origins, have a correspondingly high abundance of their
methylated counterparts, and suggest that this is caused
by sedimentary methylation of these alkylnaphthalenes.

2. Experimental
2.3. Nuclear magnetic resonance (NMR) data
2.1. Samples
All measurements were carried out in a solution of
chloroform-d using a Varian Gemini-200 spectrometer
operating at 200 MHz for 1H (ppm relative to CDCl3 at
7.25 ppm) and 50 MHz for 13C (ppm relative to CDCl3
at 77.0 ppm).
1
H-NMR data for 1,2,3,5,6,7-HMN: d 2.37, s, 6H,
Ar(C2, C6)-CH3; 2.47, s, 6H, Ar(C3, C7)-CH3; 2.57, s,
6H, Ar(C1, C5)-CH3; 7.67, s, 2H, Ar(C4, C8)-H.

13
C-NMR data for 1,2,3,5,6,7-HMN: d 14.98, 16.11,
22.05, Ar(C1, C2, C3, C5, C6, C7)-CH3; 121.95, Ar(C4,

Information about the samples is given in Table 1.
2.2. Reference compounds
1,6-DMN was purchased from Sigma. 1,2,3,5-TeMN,
1,2,3,5,6-PMN, iP-iHMN and 4-Me-iP-iHMN were
available from previous studies (Alexander et al., 1993;
Bastow et al., 1998; Ellis et al., 1996; Bastow et al., 1999).
A sample of 1,2,5-TMN was provided by Dr P. Forster.
Table 1
Geological and geochemical data for the crude oils and rock extractsa
Sample

Location

Name

Type

Country

Basin

Age or probable age
of oil source rock

MPI-1

TNR-1

PNR

%MR

Dullingari-26
GK 1959m
GK 2026m
Moorari-4

Moorari-3 71080
PD130A

Crude oil
Rock extract
Rock extract
Crude oil
Rock extract
Rock extract

Australia
Indonesia
Indonesia
Australia
Australia
Australia

Eromanga
S. Sumatra
S. Sumatra

Eromanga
Eromanga
Canning

Jurassic
Tertiary
Tertiary
Jurassic
Jurassic
Devonian

0.4
0.6
0.7
0.2
0.3
0.3

0.4
0.6

0.6
0.3
0.4
0.5

0.21
0.18
0.20
0.15
0.12
0.13

7.3
13.0
12.4
8.0
11.8
±

a

Parameters and methods of measurement: MPI-1, GC±MS data corrected to FID response (Radke et al., 1982a,b); TNR-1 (m/z 170)
(Alexander et al., 1985); PNR (m/z 198) (Bastow et al., 1998); %MR percentage of 9-methylretene compared to retene (m/z 234, 248).

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

C8); 130.05, 130.56, 131.67, 133.93, Ar(C1, C2, C3, C4a,
C5, C6, C7, C8a).
2.4. Sample preparation
Rock samples were air dried and crushed to a ®ne
powder using a Tema mill and extracted ultrasonically
with dichloromethane:methanol (95:5). The solvent
extract was recovered by ®ltration and the solvent was
carefully removed to yield the soluble organic matter
(SOM).
2.5. Isolation of aromatic hydrocarbon fractions
In a typical separation, a crude oil or sediment extract
was subjected to liquid chromatography as follows. Glass
columns (401.2 cm i.d.) were packed with activated
silica gel (6 g, Merck, particle size 0.063±0.200 mm for
chromatography) as a slurry in n-pentane. The sample
(50±100 mg) in n-pentane was introduced to the top of the
column to produce a concentrated band. Aliphatic hydrocarbons were then eluted under gravity with n-pentane
(40 ml), aromatic hydrocarbons with n-pentane/dichloromethane (35:5, 40 ml), and polar compounds with
dichloromethane:methanol (1:1, 30 ml). The aromatic
fractions were obtained by careful removal of the solvent. The residue was dissolved in hexane to provide a
sample ready for GC±MS analysis.
2.6. Analysis by gas chromatography±mass spectrometry
(GC±MS)
Two systems were used for GC±MS analysis. One, a
Hewlett-Packard 5973 MSD, interfaced with a 6890 gas
chromatograph was ®tted with a fused-silica open tubular column (SGE, Australia, 50 m0.22 mm i.d.)
coated with BP-20 stationary phase (0.25 mm). The GC
oven temperature was programmed from 50 to 260 C at
3 C minÿ1. Samples for analysis were dissolved in hexane
and injected on-column using a HP 6890 autosampler at
an oven temperature of 50 C. Helium was used as carrier
gas at a constant pressure of 22 psi. Typical MSD conditions were: ionisation energy 70 eV; source temperature 230 C; electron multiplier voltage 1800 V.
The other system was a Hewlett-Packard 5971 MSD
interfaced with a 5890 Series II gas chromatograph ®tted
with a DB-5 (60 m0.25 mm i.d., phase thickness 0.25
mm, J&W Scienti®c) fused silica open tubular column.
Samples for analysis were dissolved in hexane and
injected on-column using a HP 5890 autosampler at an
oven temperature of 60 C. Helium was used as carrier
gas at a constant ¯ow of 1.28 ml minÿ1 and the GC
oven was temperature programmed from 60 to 300 C at
3 C minÿ1. Typical MSD conditions were: ionisation
energy 70 eV; source temperature 200 C; electron multiplier voltage 2200 V.

525

Individual alkylnaphthalenes in crude oils and sediment extracts were identi®ed by mass chromatography
on the basis of mass spectra and by co-chromatography
with authentic reference compounds.
2.7. Methylation experiments
The aluminum montmorillonite used in the study was
material prepared for an earlier study (Alexander et al.,
1984). Reagents were used in the following proportions;
alkylnaphthalenes (1 mg), and hexamethylbenzene (3
mg), pentadecane (0.5 mg)(normalisation standard) and
®nely divided aluminum montmorillonite (10 mg).
These reagents were placed in small (1 ml) Pyrex glass
ampoules and ¯ushed with dry nitrogen. The ampoules
were evacuated, sealed and then heated to 120 C for
various times. The contents were extracted with
dichloromethane (2 ml), the solvent was removed by
careful distillation, and hexane (1.8 ml) containing the
external standard hexadecane (0.5 mg) was added. An
aliquot was then subjected to analysis using GC±MS
techniques.

3. Results and discussion
3.1. Laboratory methylation of alkylnaphthalenes
Laboratory experiments were carried out to show that
methyl derivatives of alkylnaphthalenes could be formed
via clay-catalysed methylation reactions. Samples of
alkylnaphthalenes were heated with hexamethylbenzene
(methyl donor) and aluminum montmorillonite at 120 C
for various times and the reaction mixtures analysed
using GC±MS techniques. The partial mass chromatograms of each of the reaction mixtures are shown in
Figs. 1a±5a together with the percentage conversion to
each reaction product. Reactions were stopped at low
conversions to avoid interferences due to other reactions
such as isomerisation, transalkylation and dealkylation.
In each case the major methylation product was the
isomer with the additional methyl located at a position
on the ring that was activated to electrophilic aromatic
substitution (EAS) and in the position with the least
steric hindrance from adjacent methyl groups. Experimentally determined preferred substitution positions for
the alkylnaphthalenes used in this study are arrowed in
Fig. 6. In particular, aromatic (naphthalene) carbons
located at positions adjacent to or three or ®ve carbons
from the position of attachment of an alkyl substituent
are activated to EAS in a similar manner as an alkyl
substituent on a benzene ring would activate the ortho
and para positions. However, while the alkyl substituents a€ect the activation of carbons in both rings
(naphthalene) to EAS, the e€ect is greatest in the ring to
which the alkyl substituents are attached (Ansell et al.,

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T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

1979). Furthermore, positions adjacent to alkyl substituents
were found to be unfavourable to EAS due to steric
hindrance, with peri positions (e.g. positions 1 and 8)
having the greatest steric hindrance and positions adjacent

to multiple alkyl substituents more sterically hindered
than those located adjacent to a single alkyl substituent.
The positions with electronic activation to EAS for the
compounds used are marked with asterisks in Fig. 6.

Fig. 1. Partial m/z (156+170) mass chromatograms (BP-20) of (a) the products of laboratory methylation experiment where 1,6DMN was heated with a methyl donor (HMB) and aluminum montmorillonite at 120 C for 8 h; (b) an aromatic fraction of GK 1959
m with a high relative abundance of 1,6-DMN and (c) an aromatic fraction of PD 130A without a high relative abundance of 1,6DMN. For peak identi®cations refer to Table 2. Percentages stated for co-chromatographing compounds were obtained from separate
analysis using BP-20 and DB-5 GC-columns.

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

In the case of 1,6-DMN the positions activated to
EAS are positions 2, 4, 5 and 7. However, only the 4
position is devoid of an adjacent methyl group, making
this the position activated to EAS with least steric hindrance. Therefore, 1,4,6-TMN should be the major
TMN formed from the methylation of 1,6-DMN. This
is a fact substantiated by the experimental results shown
in Fig. 1a. Clearly, the major methylation product is
1,4,6-TMN with only minor amounts of 1,2,6-TMN and
1,6,7-TMN formed.

527

For 1,2,5-TMN, positions 4 and 7 are activated to
EAS by only one methyl substituent and positions 3, 6
and 8 are activated by two methyl substituents. Position
7 is the only position devoid of an adjacent methyl
group, resulting in this position having the least steric
hindrance. Therefore, it is not surprising that 1,2,5,7TeMN is the major product (1,2,5,6-TeMN is a less
signi®cant product) from the methylation of 1,2,5-TMN
(Fig. 2a). Further evidence that the position of methylation represents a compromise between activation to

Fig. 2. Partial m/z (170+184) mass chromatograms (BP-5) of (a) laboratory methylation experiment where 1,2,5-TMN was heated
with a methyl donor (HMB) and aluminum montmorillonite at 120 C for 8 h; (b) an aromatic fraction of Moorari-3 71080 with a high
relative abundance of 1,2,5-TMN and (c) an aromatic fraction of GK 2026 m without a high relative abundance of 1,2,5-TMN. For
peak identi®cations refer to Table 2. Percentages stated for co-chromatographing compounds were obtained from separate analysis
using a BP-20 and DB-5 GC-column.

528

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

Fig. 3. Partial m/z (184+198) mass chromatograms (BP-20) of (a) laboratory methylation experiment where 1,2,3,5-TeMN was
heated with a methyl donor (HMB) and aluminum montmorillonite at 120 C for 8 h; (b) an aromatic fraction of Moorari-4 with a
high relative abundance of 1,2,3,5-TeMN and (c) an aromatic fraction of Dullingari-26 sample without a high relative abundance of
1,2,3,5-TeMN. For peak identi®cations refer to Table 2.

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

EAS and steric hindrance is shown from the comparison
of the methylation products of 1,2,5-TMN and 1,2,3,5TeMN. It is evident from Fig. 6c that position 7 of
1,2,3,5-TeMN is now activated by two methyl substituents (positions 1 and 3), and is still free of adjacent
methyl substituents. Therefore, position 7 is the site with
greatest activation to EAS with the least steric hindrance. This hypothesis agrees well with the products
formed from the methylation of 1,2,3,5-TeMN (Fig. 3a)
where 1,2,3,5,7-PMN was the major product, and
1,2,3,5,6-PMN was a minor product. Clearly, from the
comparison of the methylation products of 1,2,5-TMN
and 1,2,3,5-TeMN, a methyl substituent in one naphthalene ring can e€ect the activation of positions to EAS in
the other ring. From this comparison it is also apparent
that the steric hindrance caused by an adjacent methyl

529

substituent can e€ect the orientation of methylation as
strongly as electronic e€ects resulting from alkyl substituents.
Similar reasoning was used to explain the methylation
products of 1,2,3,5,6-PMN (Fig. 6d). Of the three
vacant positions, two (positions 4 and 8) are located peri
to existing methyl substituents. This leaves only the 7
position available to methylation, a preferred position
for methylation according to the results (Fig. 4a).
Again the 1,6-alkyl substition pattern of iP-iHMN
results in a similar substitution pattern to that outlined
for 1,6-DMN. Positions 4, 5 and 7 are activated by the
two alkyl substituents. Of these positions only the 4
position has no adjacent alkyl substituents, and positions 5 and 7 are located adjacent to an isopropyl substituent resulting in greater steric hindrance for these

Fig. 4. Partial m/z (198+212) mass chromatograms (BP-20) of (a) laboratory methylation experiment where 1,2,3,5,6-PMN was
heated with a methyl donor (HMB) and aluminum montmorillonite at 120 C for 1 h and (b) an aromatic fraction of GK 1959 m with
a high relative abundance of 1,2,3,5,6-PMN. For peak identi®cations refer to Table 2.

530

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

two positions. The other two vacant positions (3 and 8)
are activated by a single methyl substituent and both
experience steric hindrance from adjacent alkyl groups
substituents. Hence, position 4 is the preferred position
of attack resulting in the formation of 4-Me-iP-iHMN.
The methylation reagent (HMB) used in these
laboratory methylation reactions was chosen because of
its labile methyl groups. We do not suggest that this is
the actual methylating agent in sedimentary material.
Potential methylating reagents in sedimentary material
may be compounds containing gem and angular methyl
groups, which on aromatisation are likely to produce
active methyl groups. Other sources for methylation
reagents may include alkylaromatics undergoing acid
catalysed dealkylation. Also, during the coali®cation of
lignin the methyl of methoxyl groups is released (Botto
et al., 1989). However, the source of the methylating
reagents in sedimentary matter is uncertain.

3.2. Methylation in sediments
Crude oils and sediment extracts contain isomers of
methylated naphthalenes that have no obvious natural
product origin. The formation of these compounds has
been suggested to be from processes such as isomerisation and transalkylation. Therefore, these methylated
naphthalenes are present in all crude oils and sediments
that have some input of alkylnaphthalenes from natural
products. However, when these alkylnaphthalenes of
natural product origins are in high abundance the distributions of methylated naphthalenes formed directly
from these alkylnaphthalenes are likely to be enhanced
relative to the normal levels formed from other isomerisation and transalkylation reactions.
The co-occurrence in sedimentary organic matter of
anomalously high abundances of certain alkylnaphthalenes and their methylated counterparts suggests a link,

Fig. 5. Partial m/z (197+211) mass chromatograms (BP-5) of (a) laboratory methylation experiment where iP-iHMN was heated with
a methyl donor (HMB) and aluminum montmorillonite at 120 C for 1 h and (b) the Moorari-4 aromatics fraction where iP-iHMN cooccurs with its methylated counterpart 4-Me-iP-iHMN. For peak identi®cations refer to Table 2.

531

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

possibly involving sedimentary methylation. To investigate this relationship we have analysed low maturity
samples with anomalously high abundances of 1,6-DMN,
1,2,5-TMN, 1,2,3,5-TeMN, 1,2,3,5,6-PMN and iP-iHMN
and obtained relative abundance data for their corresponding methylated counterparts such that an enhancement can be observed in the resultant isomer distribution.
Low maturity samples were used in this study, because
these samples still retain an abundance of alkylnaphthalenes derived from natural product precursors
that may be depleted with maturity (Alexander et al.,

Fig. 6. The positions of alkylnaphthalenes activated to EAS ()
for (a) 1,6-DMN, (b) 1,2,5-TMN, (c) 1,2,3,5-TeMN, (d)
1,2,3,5,6-PMN and (e) iP-iHMN. Each  indicates the ring
positions activated by each of the alkyl group(s) highlighted in
bold. Arrow ( ) represents experimentally determined preferred positions of methylation.

1985, 1986, 1993; Strachan et al., 1988; van Aarssen et
al., 1999). In the case of the 1,6-DMN, two samples
(GK 1959 m and PD 130A) were selected for comparison. The laboratory experiments for the methylation of
1,6-DMN (Fig. 1a) showed that 1,4,6-TMN was the
predominant methylation product. Comparison of this
methylation reaction product to a sedimentary sample
Table 2
Compounds identi®ed in crude oils and rock extracts
Peak
no.a

Compound

Abbreviation

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42

2,6-Dimethylnaphthalene
2,7-Dimethylnaphthalene
1,7-Dimethylnaphthalene
1,3-Dimethylnaphthalene
1,6-Dimethylnaphthalene
1,4-Dimethylnaphthalene
2,3-Dimethylnaphthalene
1,5-Dimethylnaphthalene
1,2-Dimethylnaphthalene
1,3,7-Trimethylnaphthalene
1,3,6-Trimethylnaphthalene
1,4,6-Trimethylnaphthalene
1,3,5-Trimethylnaphthalene
2,3,6-Trimethylnaphthalene
1,2,7-Trimethylnaphthalene
1,6,7-Trimethylnaphthalene
1,2,6-Trimethylnaphthalene
1,2,4-Trimethylnaphthalene
1,2,5-Trimethylnaphthalene
1,2,3-Trimethylnaphthalene
1,3,5,7-Tetramethylnaphthalene
1,3,6,7-Tetramethylnaphthalene
Cadalene
1,4,6,7-Tetramethylnaphthalene
1,2,4,7-Tetramethylnaphthalene
1,2,4,6-Tetramethylnaphthalene
1,2,5,7-Tetramethylnaphthalene
2,3,6,7-Tetramethylnaphthalene
1,2,6,7-Tetramethylnaphthalene
1,2,3,7-Tetramethylnaphthalene
1,2,3,6-Tetramethylnaphthalene
1,2,5,6-Tetramethylnaphthalene
1,2,3,5-Tetramethylnaphthalene
1,2,4,6,7-Pentamethylnaphthalene
1,2,3,5,7-Pentamethylnaphthalene
1,2,3,6,7-Pentamethylnaphthalene
1,2,3,5,6-Pentamethylnaphthalene
4-Methyldibenzothiophiene
1,2,3,5,6,7-Hexamethylnaphthalene
3-Methyldibenzothiophiene
2-Methyldibenzothiophiene
6-Isopropyl-2-methyl-1-(4-methylpentyl)naphthalene
6-Isopropyl-2,4-dimethyl-1(4-methylpentyl)naphthalene

2,6-DMN
2,7-DMN
1,7-DMN
1,3-DMN
1,6-DMN
1,4-DMN
2,3-DMN
1,5-DMN
1,2-DMN
1,3,7-TMN
1,3,6-TMN
1,4,6-TMN
1,3,5-TMN
2,3,6-TMN
1,2,7-TMN
1,6,7-TMN
1,2,6-TMN
1,2,4-TMN
1,2,5-TMN
1,2,3-TMN
1,3,5,7-TeMN
1,3,6,7-TeMN
Cad
1,4,6,7-TeMN
1,2,4,7-TeMN
1,2,4,6-TeMN
1,2,5,7-TeMN
2,3,6,7-TeMN
1,2,6,7-TeMN
1,2,3,7-TeMN
1,2,3,6-TeMN
1,2,5,6-TeMN
1,2,3,5-TeMN
1,2,4,6,7-PMN
1,2,3,5,7-PMN
1,2,3,6,7-PMN
1,2,3,5,6-PMN
4-MDBT
1,2,3,5,6,7-HMN
3-MDBT
2-MDBT
iP-iHMN

43
a

Peak numbers refer to Figs. 1±5.

4-Me-iP-iHMN

532

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

(GK 1959 m) with high relative abundance of 1,6-DMN
with a sample (PD 130A) that has a lower relative
abundance of 1,6-DMN is shown in Fig. 1. From these
results it is apparent that the relative abundance of
1,4,6-TMN is enhanced in the TMNs in the sample (GK
1959 m) with the high relative abundance of 1,6-DMN
compared to the sample (PD 130A) with a lower relative
abundance of 1,6-DMN.
For the sedimentary methylation of 1,2,5-TMN the
methyl derivative 1,2,5,7-TeMN is shown for the
Moorari-3, 71080 sample and compared with the corresponding peak from the GK 2046 m sample (Fig. 2).
Comparison of the TMN and TeMN distributions of
these two samples clearly shows a higher relative abundance of 1,2,5-TMN in the Moorari sample, which is also
associated with an enhancement of 1,2,5,7-TeMN in the
TeMNs. While 1,2,5,6-TeMN is also a signi®cant product
from the laboratory methylation of 1,2,5-TMN it is dif®cult to assess the contribution of this reaction product
to the 1,2,5,6-TeMN abundance in the Moorari sample
since 1,2,5,6-TeMN also has an obvious natural product
origin in this sample (van Aarssen et al., 1999).
Results from analysis of crude oils and for the reactant 1,2,3,5-TeMN and products from the methylation
reaction (1,2,3,5,7-PMN) are shown in Fig. 3. Moorari4 is a sample exhibiting a high relative abundance of
1,2,3,5-TeMN in the TeMNs and is accompanied by an
enhanced 1,2,3,5,7-PMN peak relative to the most
stable 1,2,4,6,7-PMN (Bastow et al., 1998) in the PMNs
(Fig. 3b). This relative enhancement of 1,2,3,5,7-PMN is
apparent when compared with a more common distribution of PMNs in the Dullingari-26 sample (Fig. 3c).
In this case a lower abundance of 1,2,3,5-TeMN in the
TeMNs is also associated with a lower abundance of
1,2,3,5,7-PMN relative to the stable 1,2,4,6,7-PMN.
The methylation reaction of 1,2,3,5,6-PMN (Fig. 4a)
shows that 1,2,3,5,6,7-HMN is formed as the only reaction product. Corresponding high concentrations of the
substrate 1,2,3,5,6-PMN and product 1,2,3,5,6,7-HMN
are shown in Fig. 4b for sample GK 1959 m. The high
relative abundance of 1,2,3,5,6-PMN in the PMNs is
shown together with the previously unidenti®ed
1,2,3,5,6,7-HMN. This relationship suggests that sedimentary methylation has occurred and is the source of
1,2,3,5,6,7-HMN.
Comparison of chromatograms of the experimental
methylation product of iP-iHMN (Fig. 5a) with that of
the Moorari-4 sample (Fig. 5b) showed evidence for the
methylation product of iP-iHMN in the crude oil. This
result suggests that a signi®cant amount of sedimentary
methylation has occurred to the parent compound.
The co-occurrences of 1,6-DMN, 1,2,5-TMN, 1,2,3,5TeMN, 1,2,3,5,6-PMN and iP-iHMN with their methylated counterparts in enhanced levels in sedimentary samples
suggests a precursorproduct relationship between these
compounds, and is strong evidence that methylation is a

geosynthetic process. Further supporting evidence is
provided by the fact that the carbon skeleton of these
methylated alkylnaphthalenes is uncommon in natural
products and the occurrence of 1,2,3,5,6,7-HMN, due to
its high level of substitution, has no obvious natural
product precursor and is dicult to explain without a
methylation process. Additional support that geosynthetic
methylation has occurred in the sample suite used in this
study is provided by the occurrence of 9-methylretene in
most of the samples. The percentage of 9-methylretene
compared to retene for the samples used in this study is
given in Table 1 (%MR). 9-Methylretene was identi®ed
by Alexander et al. (1995) as a methylation product of
retene and its presence in all but one of the samples used
in this study is supporting evidence that methylation has
occurred in these samples.
The results of this study demonstrate that the distributions of methylated alkylnaphthalenes in crude oils
and sediments are a€ected by the distributions of the
corresponding class of alkylnaphthalenes. Therefore,
these results support the proposal of van Aarssen et al.
(1999) that the distributions of TMNs, TeMNs and
PMNs in crude oils are closely related due to isomerisation and transalkylation reactions, in which the methyl
groups involved in these reactions form a `methyl pool'
to which every compound in a crude oil has access. This
suggests that the methylating reagents in nature may
include the methyl aromatic compounds themselves.

4. Conclusions
1,2,3,5,6,7-Hexamethylnaphthalene has been synthesised and identi®ed in sedimentary material. Low
maturity crude oils and rock extracts with high relative
abundances of 1,6-DMN, 1,2,5-TMN, 1,2,3,5-TeMN,
1,2,3,5,6-PMN and iP-iHMN have been shown to contain enhanced levels of their corresponding methyl
counterparts 1,4,6-TMN, 1,2,5,7-TeMN, 1,2,3,5,7-PMN,
1,2,3,5,6,7-HMN and 4-Me-iP-iHMN respectively.
Laboratory methylation reactions carried out under
mild conditions show that these alkylnaphthalenes are
readily methylated in speci®c positions and the distributions of the methylated alkylnaphthalenes formed
are consistent with those in sedimentary samples. The
mechanism for the methylation of the alkylnaphthalenes is
consistent with electrophilic aromatic substitution with
steric hindrance strongly in¯uencing the reaction products.
These results have been interpreted as evidence for a
sedimentary electrophilic aromatic methylation process.

Acknowledgements
Geo€ Chidlow is thanked for his assistance with GC±
MS analysis. Dr Iman B. Sosrowidjojo and Lemigas are

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

thanked for the GK well samples used in this paper.
Financial support was provided by the Australian Petroleum Co-operative Research Centre and from a Curtin
University Postgraduate Scholarship. We also thank Dr.
C.A. Lewis and an anonymous reviewer for their critical
reviews of the paper.
Associate EditorÐS. Rowland

References
Alexander, R., Kagi, R.I., Larcher, A.V., 1984. Clay catalysis
of alkyl hydrogen exchange reactions Ð reaction mechanisms. Organic Geochemistry 6, 755±760.
Alexander, R., Kagi, R.I., Rowland, S.J., Sheppard, P.N.,
Chirila, T.V., 1985. The e€ects of thermal maturity on distribution of dimethylnaphthalenes and trimethylnaphthaplenes in some Ancient sediments and petroleums.
Geochimica et Cosmochimica Acta 49, 385±395.
Alexander, R., Strachan, M.G., Kagi, R.I., van Bronswijk, W.,
1986. Heating rate e€ects on aromatic maturity indicators.
Geochimica et Cosmochimica Acta 52, 1255±1264.
Alexander, R., Bastow, T.P., Kagi, R.I., Singh, R.K., 1992.
Identi®cation of 1,2,2,5-tetramethyltetralins and 1,2,2,5,6-pentamethyltetralin as racemates in petroleum. Journal of the
Chemical Society, Chemical Communications 23, 1712±1714.
Alexander, R., Bastow, T.P., Fisher, S.J., Kagi, R.I., 1993.
Tetramethylnaphthalenes in crude oils. Polycyclic Aromatic
Compounds 3, 629±634.
Alexander, R., Bastow, T.P., Fisher, S.J., Kagi, R.I., 1995.
Geosynthesis of organic compounds: II. Methylation of
phenanthrene and alkylphenanthrenes. Geochimica et Cosmochimica Acta 59, 4259±4266.
Ansell, H.V., Sheppard, P.J., Simpson, C.F., Stroud, M.A.,
Talyor, R., 1979. Electrophilic aromatic substitution. Part 22.
The e€ect of methyl sustituents on detritation of the 9-position of phenanthrene; tritium migration during exchange.
Journal of the Chemical Society. Perkin I, 381±385.
Araki, M., Mukaiyama, T., 1974. Reaction of mixed carboxylic
anhydrides with Grignard reagents. A useful method for the
preparation of ketones. Chemistry Letters, 663±666.
Bastow, T.P., Alexander, R., Kagi, R.I., 1996. Geosynthesis of
organic compounds IV. Methylation of 1,2,7-trimethylnaphthalene. Polycyclic Aromatic Compounds 9, 177±183.
Bastow, T.P., Alexander, R., Sosrowidjojo, I.B., Kagi, R.I.,
1998. Pentamethylnaphthalenes and related compounds in
sedimentary organic matter. Organic Geochemistry 28, 585±
595.
Bastow, T.P., van Aarssen, B.G.K., Alexander, R., Kagi, R.I.,
1999. Biodegradation of aromatic land-plant biomarkers in
some Australian crude oils. Organic Geochemistry 30, 1229±
1239.
Botto, R.E., Hayatsu, R., Carrado, K.A., Winans, R.E., 1989.
Isotope labeling investigations in simulated coali®cation: a
view of geological metamorphism. Proc. 1989 Intl. Conf.
Coal Sci. 1, 1±4.
Chen, T.S., Canonne, P., Leitch, L.C., 1973. Synthesis of 1,2,3trimethyl-, 1,2,3,7-tetramethyl-, and 1,2,3,5,6,7-hexamethylnaphthalenes. Synthesis 620±621.

533

Derbyshire, F.J., Whitehurst, D.D., 1981. Study of coal conversion in polycondensed aromatic compounds. Fuel 60,
655±662.
Ellis, L., 1994. Aromatic hydrocarbons in crude oil and sediments: molecular sieve separations and biomarkers. PhD
dissertation, Curtin University of Technology.
Ellis, L., Singh, R.K., Alexander, R., Kagi, R.I., 1995. Geosynthesis of organic compounds: III. Formation of alkyltoluenes and alkylxylenes in sediments. Geochimica et
Cosmochimica Acta 59, 5133±5140.
Ellis, L., Singh, R.K., Alexander, R., Kagi, R.I., 1996. Formation of isohexyl alkylaromatic hydrocarbons from aromatization-rearrangement of terpenoids in the sedimentary
environment: a new class of biomarker. Geochimica et Cosmochimica Acta 60, 4747±4763.
Forster, P.G., Alexander, R., Kagi, R.I., 1989. Identi®cation of
2,2,7,8-tetramethyl-1,2,3,4-tetrahydronaphthalene in petroleum. Journal of the Chemical Society, Chemical Communications 5, 274±276.
He, S.J.X., Long, M.A., Attalla, M.I., Wilson, M.A., 1992.
Methylation of naphthalene by methane over substituted
aluminophosphate molecular sieves. Energy and Fuels 6,
498±502.
He, S.J.X., Long, M.A., Attalla, M.I., Wilson, M.A., 1994.
Methylation of naphthalene by methane-13C over copperexchanged silicoaluminophosphate. Energy and Fuels 8,
286±287.
He, S.J.X., Long, M.A., Wilson, M.A., Gorbaly, M.L., 1995.
Methylation of benzene by methane-13C over zeolitic catalysts at 400 C. Energy and Fuels 9, 616±619.
Ioppolo-Armanios, M., Alexander, R., Kagi, R.I., 1995. Geosynthesis of organic compounds. I-Alkylation of sedimentary
phenols. Geochimica et Cosmochimica Acta 59, 3017±3027.
Killops, S.D., 1991. Novel aromatic hydrocarbons of probable
bacterial origin in a Jurassic lacustrine sequence. Organic
Geochemistry 17, 25±36.
Martin, E.L., 1942. The clemmensen reduction. Organic Reactions 1, 155±209.
PuÈttmann, W., Villar, H., 1987. Occurrence and geochemical
signi®cance of 1,2,5,6-tetramethylnaphthalene. Geochimica
et Cosmochimica Acta 51, 3023±3029.
Radke, M., Welte, D.H., Willsch, H., 1982a. Geochemical
study on a well in the Western Canada Basin: relation of the
aromatic distribution pattern to maturity of organic matter.
Geochimica et Cosmochimica Acta 46, 1±10.
Radke, M., Willsch, H., Leythaeuser, D., 1982b. Aromatic
components of coal: relation of distribution pattern to rank.
Geochimica et Cosmochimica Acta 46, 1831±1848.
Radke, M., Garrigues, P., Willsch, H., 1990. Methylated
dicyclic and tricyclic aromatic hydrocarbons in crude oils
from the Handil ®eld, Indonesia. Organic Geochemistry 15,
17±34.
Radke, M., Rullkotter, J., Vriend, S.P., 1994. Distribution of
naphthalenes in crude oils from Java Sea: source and
maturation e€ects. Geochimica et Cosmochimica Acta 58,
3675±3689.
Smith, J.W., George, S.C., Batts, B.D., 1994. Pyrolysis of aromatic compounds as a guide to synthetic reactions in sediments. The APEA Journal 34, 231±240.
Smith, J.W., George, S.C., Batts, B.D., 1995. The geosynthesis
of alkylaromatics. Organic Geochemistry 23, 71±80.

534

T.P. Bastow et al. / Organic Geochemistry 31 (2000) 523±534

Strachan, M.G., Alexander, R., Kagi, R.I., 1988. Trimethylnaphthalenes in crude oils and sediments: e€ects of
source and maturity. Geochimica et Cosmochimica Acta 52,
1255±1264.
van Aarssen, B.G.K., Hessels, J.K.C., Abbink, O.A., de Leeuw,
J.W., 1992. The occurrence of polycyclic sesqui-, tri- and
oligoterpenoids derived from a resinous polymeric cadinene
in crude oils from South East Asia. Geochimica et Cosmochimica Acta 56, 1231±1246.

van Aarssen, B.G.K., Bastow, T.P., Alexander, R., Kagi,
R.I., 1999. Distributions of methylated naphthalenes in
crude oils: indicators of maturity, biodegradation and mixing. Organic Geochemistry 30, 1213±1227.
van Duin, A.C.T., Baas, J.M.A., van de Graaf, de Leeuw, J.W.,
Bastow, T.P., Alexander, R., 1997. Comparison of calculated
equilibrium mixtures of alkylnaphthalenes and alkylphenanthrenes with experimental and sedimentary data Ð the importance
of entropy calculations. Organic Geochemistry 26, 275±280.