A novel synthesis of branched high-molecular-weight (C40 +) long-chain alkanes

Article abstract of DOI:10.1271/bbb.66.523

Many biological and geochemical questions remain concerning the structures, functions, and properties of naturally occurring high-molecular-weight (C ₄₀⁺) alkanes with various mid-chain alkylation patterns. Above C₄₀, these alkanes are exceedingly difficult to separate and purify, and syntheses can be blocked by the low solubility of intermediates. To overcome these problems, a facile three-step synthesis employing the alkylation of 1,3-dithiane with a suitable α,ω-dibromoalkane was developed. Bisalkylation of the bis(dithianyl)alkane intermediate with the appropriate 1-bromoalkane and subsequent desulfurization with Raney nickel furnished the desired long-chain alkane. Long-chain alkanes modified at mid-chain and/or symmetrically near the chain termini (or unmodified, i.e., long-chain n-paraffins) are accessible by the selection of appropriate bromoalkanes. Nine mid-chain methylated (C₃₈H₇₈ to C₅₃H ₁₀₈), one symmetrical terminal-chain dimethylated (C ₄₀H₈₂), and four linear (C₄₄H₉₀ to C₅₈H₁₁₈) long-chain alkanes were synthesized by using this approach. High-temperature gas chromatography (HTGC) was found to have important advantages for evaluating the purity of the synthetic high-molecular-weight alkanes.

Full text of DOI:10.1271/bbb.66.523

Bioscience, Biotechnology, and Biochemistry
ISSN: 0916-8451 (Print) 1347-6947 (Online) Journal homepage: http://www.tandfonline.com/loi/tbbb20
A Novel Synthesis of Branched High-molecular-
+
weight (C40 ) Long-chain Alkanes
Hans-Joachim LEHMLER, Robert G. BERGOSH, Mark S. MEIER & Robert M. K.
CARLSON
To cite this article: Hans-Joachim LEHMLER, Robert G. BERGOSH, Mark S. MEIER & Robert M.
K. CARLSON (2002) A Novel Synthesis of Branched High-molecular-weight (C40 +) Long-chain
Alkanes, Bioscience, Biotechnology, and Biochemistry, 66:3, 523-531, DOI: 10.1271/bbb.66.523
To link to this article: http://dx.doi.org/10.1271/bbb.66.523
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Date: 11 November 2015, At: 05:23

Biosci. Biotechnol. Biochem., 66 (3), 523–531, 2002
+
A Novel Synthesis of Branched High-molecular-weight (C40
Long-chain Alkanes
)
Hans-Joachim LEHMLER,† Robert G. BERGOSH,a Mark S. MEIER
and Robert M. K. CARLSON
,
a
b
Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40536, U.S.A.
aDepartment of Chemistry, University of Kentucky, Lexington, KY 40506, U.S.A.
bChevron Research & Technology Company, P.O. Box 1627, Richmond, CA 94802, U.S.A.
Received August 20, 2001; Accepted October 30, 2001
chemical properties of these C40+ long-chain alkanes.
Many biological and geochemical questions remain
concerning the structures, functions, and properties of
Terrestrial organisms use these higher-molecular-
weight alkanes as cuticular waxes to regulate the
uptake and loss of water, act as a barrier against
microorganisms, prevent the penetration of inorgan-
ic chemicals, aŠect the absorption of agricultural
chemicals, and play a role in chemosensory com-
munication.3) Numerous insect classes contain long-
chain alkanes with species- or class-speciˆc internal
methylation patterns in which certain isomers may
act as pheromones or kariomones.3)
+
naturally occurring high-molecular-weight (C40
)
alkanes with various mid-chain alkylation patterns.
Above C40, these alkanes are exceedingly di‹cult to
separate and purify, and syntheses can be blocked by
the low solubility of intermediates. To overcome these
problems, a facile three-step synthesis employing the
alkylation of 1,3-dithiane with
a suitable a,v-
dibromoalkane was developed. Bisalkylation of the
bis(dithianyl)alkane intermediate with the appropriate
1-bromoalkane and subsequent desulfurization with
Raney nickel furnished the desired long-chain alkane.
Long-chain alkanes with internal alkyl modiˆca-
tion are components of petroleum microcrystalline
waxes and are associated with the organic scale that
causes oil-ˆeld production problems involving the
fouling of wells, pipelines, and petroleum reser-
voirs.4–6) The carbon number predominance patterns
of these higher alkanes can also provide geological
information on the source rock paleodepositional en-
vironment that is useful in petroleum exploration.4)
Long-chain alkanes modiˆed at mid-chain and or sym-
W
metrically near the chain termini (or unmodiˆed, i.e.,
long-chain n-para‹ns) are accessible by the selection of
appropriate bromoalkanes. Nine mid-chain methylated
(C38H78 to C53H108), one symmetrical terminal-chain
dimethylated (C40H82), and four linear (C44H90 to C58H118
)
long-chain alkanes were synthesized by using this
approach. High-temperature gas chromatography
(HTGC) was found to have important advantages for
evaluating the purity of the synthetic high-molecular-
weight alkanes.
＋
The importance and diversity of the C40 alkanes
have become evident with the availability of in-
strumental techniques such as high-temperature gas
chromatography (HTGC).4–6)
The structures of a branched long-chain alkane
may not be unequivocally assigned by GC-MS
alone.7) Modern methods using meta-stable reaction
monitoring or triple quadrapole mass spectrometers
aid this assignment, but cannot be applied for
alkanes with a carbon number above about C40.8)
Moreover, the isolation of individual higher-
molecular-weight alkanes from complex mixtures of
similar isomers in a biological or geochemical extract
may be virtually impossible. Therefore, access to syn-
thetic standards is essential for determining chemical
structures and characteristics, and for use in model
studies.
Key words: long-chain alkane; linear alkane; bran-
ched alkane; dithiane
Long-chain, internally modiˆed (e.g. methylated)
alkanes are widely distributed in the natural environ-
ment, occurring in extremeophillic bacteria, certain
algae, many terrestrial plants and animals, and in ge-
ological deposits ranging in age from recent to the
Proterozoic period.1–3) The higher-molecular-weight
members (containing greater than 40 carbon atoms,
i.e. C40+) of this class of alkanes are important com-
ponents of the surface waxes of insects and the
higher-molecular-weight fractions of petroleum.3–6)
Many questions remain concerning the chemical
structures, biological functions and physical and
A
variety of synthetic methods have been
employed to prepare long-chain alkanes, including
oligomerization of bifunctional starting materi-
†
To whom correspondence should be addressed. Phone: +1-859-268-5276; Fax: +1-859-323-1059; E-mail: hjlehm1
＠
uky.edu

524
H-J. LEHMLER et al.
Scheme 1. Synthesis of Linear and Branched Long-chain Alkanes 2.
als,9–11) alkylation of
b
-keto esters,12) extension of
logs in this high-molecular-weight range can be ex-
carboxylic acids with 1-morpholinocyclodecene,13,14)
Blaise ketone synthesis,13) Wurtz coupling12,13,15,16) and
the Wittig reaction.17–21) All of these methods can
produce only linear long-chain alkanes. Further-
more, in some cases, it is unclear whether the alkane
products were pure or contained near-homolog con-
taminants. Methyl- and dimethyl branched alkanes
and related compounds have been synthesized by us-
ing several reactions, but the Grignard and related
reactions are most frequently employed in the synthe-
sis of branched hydrocarbon chains.22–25) However,
most published syntheses report the synthesis of
ceedingly di‹cult. The functional group or `linker'
used to connect the alkyl chain segments together
should improve the solubility of the product in or-
ganic solvents. Many alkanes in this molecular
weight range have extremely low solubility that can
decrease exponentially with increasing carbon num-
ber. The linker should also facilitate detection of the
desired product and be easily removed in the ˆnal
step of the synthesis. A fast and accurate analytical
method for the characterization of high-molecular-
weight alkane products and veriˆcation of their puri-
ty has also been sought.
alkanes of moderate chain length (
º
C40).
In the present study, we report the novel applica-
tion of the extension of linear or appropriately modi-
ˆed (e.g. methylated) bis(dithianyl)alkanes 1 to the
synthesis of long-chain alkanes 2 with a chain length
of C40 and larger by using 1,3-dithiane as a linker
group. A signiˆcant advantage of this approach is
that three alkane fragments of moderate chain length
(and reasonable solubility) are assembled in the ˆnal
synthetic step to form the desired long-chain alkane
of signiˆcantly low solubility. As shown in Scheme 1,
Results and Discussion
A procedure has been needed for the rapid prepa-
ration of many individual C40 and larger alkanes with
various internal alkylation patterns. The procedure
has to allow easy separation of the products from by-
products and starting materials at each step of the
synthesis. Separation and puriˆcation of near homo-

Synthesis of Branched Long-chain Alkanes
525
Table 1. Synthesis of Bis(dithianyl)alkanes 1
Product
Temperature (lithiation) [
9
C]
Temperature (alkylation) [
9
C]
Yield [
61
78–79
78–85
41
z
]
9
Mp [ C]
1a
1b
1b
1c
1d
1d
1e
1f
„45
„45
„10
„45
„10
„10
„15 to 4
„15
„15
„15
„30
„10
„10
„30
„10
4
„15 to 4
„15
„15
„15
85
85
98–99
—
18–32
70–95
57
37–54
48
74
oil
oil
oil
oil
1g
1h
Table 2. Bisalkylation of Bis(dithianyl)alkanes 1
Dithiane
1-Bromoalkane
Temperature [
9
C]
Monoalkylated (7)
Bisalkylated (6)
(1)
(5)
Lithiation
Alkylation
Yield [
z]
Mp [
9C]
Yield [
z
]
Mp [9C]
1a
1b
1c
1e
1e
1e
1e
1f
1g
1g
1h
5fa
5fa
5fa
5bb
5db
5ec
5fd
5cc
5cc
5dc
5cc
„10
„20
23
„10
„10
„10
„15
„15
„15
„15
„15
„15
„15
„15
7a
7d
7e
7g
7h
7i
7j
7k
7l
7
5
oil
6a
6d
6e
6g
6h
6i
6j
6k
6l
50–67
67
36
47
66
62
45
71
55
57–58
39
39
33–36
44–45
40–45
56–58
oil
37–38
31–32
oil
oil
oil
32–33
—
—
—
—
24
20
11
„15
„15
„15
„15
„15
„15
„15
„15
(13)nc
12
—
—
—
—
oil
oil
oil
7m
7n
6m
6n
16
77
a
b
c
1-Bromoalkane 5
＝
3.0 equivalents; n-BuLi
＝
3.0 equivalents.
1-Bromoalkane 5
＝
＝
3.2 equivalents; n-BuLi
4.0 equivalents.
＝
3.2 equivalents;
1-Bromoalkane 5 3.0
＝
d
nc
equivalents; n-BuLi
＝
3.2 equivalents.
1-Bromoalkane 5
＝
3.0 equivalents; n-BuLi
The compound was not fully characterized.
the ˆrst step in our approach was the alkylation of
1,3-dithiane26) (3) with suitable dibromoalkane 4.
Bisalkylation of resulting bis(dithianyl)alkane 1 with
1-bromoalkane 5 furnished desired long-chain com-
pounds 6 as well as small amounts of monoalkylated
compounds 7. Alkanes 2 were obtained in the third
step after hydrogenolysis with Raney nickel in cyclo-
hexane.27,28)
„10
9
C, although 1d was obtained in a yield of only
18–32
z
at 4 C. The low reactivity of 4d toward the
9
nucleophile (i.e. the anion of 3) is probably ascriba-
ble to steric hindrance due to the methyl substituent
adjacent to the reaction site, which might have
caused the elimination of HBr under the basic reac-
tion conditions employed.
Bisalkylation of bis(dithianyl)alkanes
1
Synthesis of bis(dithianyl)alkanes
1
Bis(dithianyl)alkanes 1a-c as well as higher 1-
bromoalkanes such as 5f are insoluble in THF at a
Bisdithianes 1 were obtained by alkylating 1,3-
dithiane (3) with dibromides 4 (see the table in
Scheme 1) in THF (Table 1). The yield of the alkyla-
tion reaction was highly temperature dependent, the
optimal temperature range for the alkylation of 4a-c
9
temperature below „30 to „25 C. In our ex-
perience, the solubility of these compounds decreases
dramatically with increasing chain length. As a
result, the lithiation of 1c requires a much higher
and 4e-h being „15
dibromoalkanes 4a-c are insoluble in THF at a tem-
perature below „30 C. Linear dibromides with a
9C to „10
9C. Linear
a
,
v
-
temperature (23
9C) than does the lithiation of 1a and
1b ( „10 C) (Table 2). However, performing the
Ã
9
9
alkylation reaction at a higher temperature reduces
the yield of the alkylation products. Yellow products
were observed whenever the alkylation reaction was
performed at an elevated temperature, indicating
chain length of more than 18 carbon atoms are even
less soluble in THF and, therefore, cannot be em-
ployed in this approach. Overall, the reaction of 1,3-
dithiane (3) with 4a-c and 4e-h proceeded smoothly in
a moderate to good yield (Table 1).
decomposition of the starting materials and or
W
products. This solubility problem might be circum-
vented by using a diŠerent solvent, but unfortunate-
ly, bis(dithianyl)alkanes 1a-c are even less soluble in
solvents such as ether and DME. Overall, our obser-
vations suggest that the chain length of the linear cen-
Dibromides with an adjacent branching point, for
example 4d, were found to be less suitable for this
approach. No reaction of 2-lithio-1,3-dithiane was
apparent with branched
a,v-dibromoalkane 4d at

526
H-J. LEHMLER et al.
Scheme 2. Synthesis of 9,30-Dimethyloctatriacontane 8, a Symmetrical Dimethyl Alkane.
Table 3. Monoalkylation of Bis(dithianyl)alkanes 1
Dithiane
1-Bromoalkane
n
-BuLia
eq.
Monoalkylated (7)
Yield [
Bisalkylated (6)
Yield [
(1)
(5)
eq.
z
]
z
]
b
b
b
b
e
5a
5b
5b
5b
5a
0.7
3.0
3.0
3.0
1.0
3.0
0.8
1.0
1.3
1.5
7b
7c
7c
7c
7f
33
50
39
34
47
6c
6c
6c
6c
6fb
16
22
33
40
16
a
Lithiation temperature
9 9 9 9
„10 C except for 1e at „15 C. Alkylation temperature „10 C except for 1e at „15 C.
＝ ＝
b
6f: mp
＝
39–409C
tral group should be less than eighteen methylene
groups.
from the dithiane moieties. Based on this hypothesis,
we synthesized methyl branched bis(dithianyl)
alkanes 1e-h and studied their alkylation. The
bisalkylation of 1e-h in the presence of 4 equivalents
of butyllithium and 3 equivalents of 1-bromoalkane
5 indeed yielded desired bisalkylated products 6 in a
Bisalkylation of 1d with 1-bromodocosane (5f) was
unsuccessful, only 50
being recovered at „15
However, at 4 C, we were able to isolate 34–36
the monoalkylated product. A small fraction (12
z
of the starting material (1d)
C due to decomposition.
of
9
9
z
z
)
z
good yield (45–77 , Table 2).
of an impure dialkylated product was also isolated,
but we were unable to further purify and characterize
this fraction. After desulfurizing the impure fraction,
an HTGC analysis showed a single major product
that seemed to be a branched alkane, thus providing
evidence that this fraction indeed contained the
desired bisalkylated product.
Consequently, 1,3-dibromo-2-methylpropane (4d)
was not a suitable starting material for the synthesis
of methyl branched alkanes. Not only was the
synthesis of corresponding bis(dithianyl)alkanes 1d
di‹cult, but the bisalkylation of 1d did not proceed
readily or in a good yield. In contrast to linear
bis(dithianyl)alkanes 1a-c, 1d has a branching point
(tertiary carbon) near the dithiane moieties. Is was
thus believed possible to obtain a higher yield of
desired bisalkylated products 6 by moving the
branching point, e.g. the methyl group, further away
Alkanes with more than one methyl group are
constituents of the cuticular hydrocarbons of many
insects. The symmetrical dimethylalkane, 13,23-
dimethylpentatriacontane, is a sex pheromone of the
tsetse ‰y (Glossina pallidipes).29,30) We investigated
the possibility of using our approach to synthesize
long-chain dimethylalkanes of this type, and were
able to synthesize 9,30-dimethyloctatriacontane 8 by
the bisalkylation of 1b with 1-bromo-4-methyldode-
cane 9 and subsequent desulfurization (Scheme 2).
Branched 1-bromoalkane 9 was synthesized from
citronellol by following the procedure of Mori and
co-workers,23,25) the only deviation from their syn-
thetic approach being the direct transformation of
2,6-dimethyltetradec-2-ene to 4-methyldodecanol by
reductive ozonolysis with O3 and NaBH4.

Synthesis of Branched Long-chain Alkanes
527
Table 4. Synthesis of Linear and Branched Long-chain Alkanes 2
*
Product
Name
Hexapentacontane
Formula
Yield
[
z
]
Puritya
Mp [
9
C]
Mp (lit.) [
9011)
9
C]
2a
2b
2c
2d
2f
2g
2h
2i
2j
2k
2l
2m
2n
C56H114
C44H90
C46H64
C58H118
C38H78
C40H82
C44H90
C46H94
C52H106
C43H88
C44H90
C46H94
C46H94
61
95.1
95.7
99.9
98.5
87.4
97.4
88.3
92.6
n.d.
74.0
83.2
81.8
98e
97.1
Tetratetracontane
Hexatetracontane
Octapentacontane
70(85)
79
86.0b
88.5c
98.8
86–86.543,44)
88–9043,45,46)
97–10043,47)
38(78)d
86
19-Methylheptatriacontane
20-Methylnonatriacontane
22-Methyltritetracontane
23-Methylpentatetracontane
26-Methylhenpentacontane
21-Methyldotetracontane
21-Methyltritetracontane
22-Methylpentatetracontane
21-Methylpentatetracontane
42–45
47
71
74
82
82
65
71
72
65
50–53
54–57
58–59
46–49
48–50
48–51
47–49
a
b
*
Values in parentheses are crude yields.
Purity determined from HTGC peak areas in the C15 to C90 range.
A solid state transition was observed at
c
d
e
71.3
9C.
A solid state transition was observed at 74.5
9
C.
Additional 28
z
of impure 2d was obtained from the ˆltrate, mp
＝
91
9C.
Purity based
on C10 to C90 peak intensities.
Sequential alkylation of bis(dithianyl)alkanes
1
experiments were performed with freshly prepared
Raney nickel in cyclohexane (Table 4).
Many branched alkanes could be made available
by dividing the alkylation of bis(dithianyl)alkanes 1
into two separate steps. We ˆrst optimized the
monoalkylation of bis(dithianyl)alkanes 1, a good
The principal di‹culty encountered in the ˆnal
step of the synthesis of linear alkanes was again the
solubility of the starting materials and the products.
A large excess of Raney nickel and the use of cyclo-
hexane as the solvent did not result in a pure product,
although no sulfur was present in the product as
shown by a combustion analysis. However, repeti-
tion of the desulfurization reaction furnished the
yield of monoalkylated compounds 7 (50
z
) being
obtained by using an approximately threefold excess
of butyllithium (Table 3). To our surprise, the second
alkylation step proved to be extremely di‹cult,
because monoalkylated bis(dithianyl)alkanes 7 that
were studied (see Table 3) seemed to be susceptible to
degradation in the presence of butyllithium.
pure n-alkane. The overall yields of the desulfuriza-
tion reaction were good, especially considering the
low solubility of linear long-chain alkanes even in hot
cyclohexane.
Desulfurization
DiŠerent synthetic methods, including Raney
nickel and nickel boride, have been reported for the
The linear alkanes were recrystallized from hexane
(Table 4). The purity of all compounds was
z
À93 ,
desulfurization
of
organic
compounds.31,32)
and the melting points of the synthetic linear alkanes
are in agreement with the ones reported in the litera-
ture. No attempts were made to desulfurize 6e be-
cause of the expected solubility problems. All methyl
branched alkanes 2 and their precursors 6 were sig-
niˆcantly more soluble in cyclohexane. The desul-
furization of these compounds was therefore relative-
ly easy, less hazardous, and only one desulfurization
step was usually required to obtain desired alkanes 2
(Table 4). The high solubility of these compounds
Methods for the desulfurization of sulfur-rich ge-
omacromolecules are of particular interest for our
synthetic approach because of the structural analogy
(long hydrocarbon chains) of these compounds to bis-
alkylated bis(dithianyl)alkanes 6. Several desulfuri-
zation methods have been developed for these ubi-
quitous organic sulfur compounds because they are
potentially valuable paleo-environmental indicators.
Raney nickel in ethanol is probably the most com-
monly employed reagent,27) but nickel boride is also a
suitable desulfurization agent.33,34) Gensler and co-
workers have described the use of Raney nickel in
cyclohexane for a synthesis of DL-methyl meromyco-
late,28) and Mori and co-wokers have employed
Raney nickel in dioxane for the synthesis of 13,23-
dimethylpenta-triacontane.30) Based on this literature
assessment, we studied the desulfurization of 6a with
made it impossible to recrystallize them from
n-
hexane. We were able to obtain su‹ciently pure sam-
ples of these alkanes by recrystallization from ace-
tone (as determined by a combustion analysis).
However, the HTGC analysis showed that all the
compounds that had been recrystallized from acetone
had a lower purity (74–93
from hexane.
z) than those recrystallized
Raney nickel in ethanol, dioxane water and cyclo-
W
hexane. We also performed some preliminary experi-
ments with nickel boride. Only cyclohexane as a sol-
vent gave the desired alkanes 2 in a satisfactory yield
and purity, and, consequently, all desulfurization
High-temperature gas chromatography
A fast analytical method for the characterization
of synthetic alkanes 2 and for veriˆcation of their
purity was also needed during this study. Conven-

528
H-J. LEHMLER et al.
±
culated values was less than 0.4z for C, H and S
tional analytical methods such as NMR, FT-IR and a
combustion analysis fail to detect even signiˆcant im-
purities of higher homologs and are therefore only of
limited value for the characterization of homologous
alkanes. HTGC has been extensively used to analyze
petroporphyrins35–37) and natural wax mixtures.4,6,38,39)
We successfully used HTGC to analyze the purity of
synthetic alkanes 2 in this study.
with all the compounds. Analytical data are given for
one representative compound with each series of
homologous compounds.
General Procedure for the Preparation of
a,v-
Bis(dithianyl)alkanes 1a-c (Table 1). A 0.58-ml
amount (2.02
M
in hexane) of butyllithium was slowly
added to a solution of 132 mg (1.1 mmol) of 1,3-
dithiane (3) and 5 mg of triphenylmethane in 15 ml of
Experimental
anhydrous THF at „45
at „45 to „30
each of -dibromides 4a-c in 5 ml of anhydrous
THF was added to the 2-lithio-1,3-dithiane solution,
and the mixture was stored at „10 C for 12 h. The
red color of the indicator vanished immediately while
adding -dibromides 4a-c. The reaction was quen-
9C. The mixture was stirred
9C for 2 h. A solution of 0.5 mmol
1,18-Dibromooctadecane (4c) was synthesized by
Li2CuCl4-mediated coupling as described earlier.40)
All methylbranched dibromides 4 were synthesized
a,v
by using standard reactions. 1,
v
-Dibromo-3-methyl-
9
alkanes 4g and 4h were respectively synthesized from
5-oxo-hexanoic acid and 7-oxo-octanoic acid. 7-Oxo-
octanoic acid was available from commercial
sources, whereas 5-oxo-hexanoic acid was prepared
from 5-oxo-hexanenitrile. After protecting the acid
function of 5-oxo-hexanoic acid and 7-oxo-octanoic
acid by esteriˆcation, the branching point was
created at the position of the carbonyl C-atom by a
Wittig-Horner-Emmons reaction with triethyl phos-
phonoacetate. Hydrogenation respectively yielded
the mixed 3-methyl-heptanedioic acid diester and 3-
methyl-nonanedioic acid diester. Reduction of these
diesters with lithium aluminum hydride and subse-
a,v
ched with 2 ml of water, and THF was evaporated
under reduced pressure. A saturated NaCl solution
(5 ml) was added, and the mixture was extracted with
ˆve 5-ml portions of dichloromethane. The com-
bined organic phases were dried over anhydrous
MgSO4, and the solvent was evaporated under
reduced pressure. Each product was obtained after
thin-layer chromatography (silica gel, hexane:
＝
dichloromethane 2:1). 1a: NMR dH (CDCl3):
1.20–1.85 (20 H, m, alkyl-C 2), 1.9 (2 H, m), 2.15
11.8 Hz, quintet, 3.4 Hz),
2.76–3.00 (8 H, m, SC 2), 4.07 (2 H, triplet,
Hz, SC S). NMR C (CDCl3): 26.05 (dithiane
26.58 (S H2), 29.18, 29.32, 29.43, 30.49, 35.44,
47.66 (S
HS). IR nmax (KBr) cm„1: 2918, 2847, 1465
H
¿
2
(2 H, doublet, JHH
＝
J
＝
＝
quent bromination with triphenylphosphine bro-
H
J
5.6
W
mine gave desired 1,
v
-dibromo-3-methyl-alkanes 4g
H
C
C
d
C
H2),
and 4h. Two similar compounds (4e and 4f) were syn-
thesized by a similar reaction sequence. 3-Methyl-
glutaric acid and 3-methyladipic acid were esteriˆed,
and the obtained diesters were reduced with lithium
aluminum hydride in THF. We found it advan-
tageous to hydrolyze these reaction mixtures with
Rochelle salt because 3-methyl-1,5-pentanediol and
3-methyl-1,6-hexanediol were obtained in good
yields.41) The diols were transformed into dibromides
(CH2 scissor), 1421 (SCH2), 1276, 1177, 906, 762, 719
(CH2 rocking). Anal. Found: C, 56.87; H, 8.96; S,
33.82
33.82
z
z
. Calcd. for C18H34S4: C, 57.12; H, 9.06; S,
.
General procedure for the preparation of
a,v-
branched bis(dithianyl)-alkanes 1d-h (Table 1). 1,3-
Dithiane (3) was lithiated as just described. Each
dibromide 4d-h was added to the solution of 2-lithio-
4e and 4f with PPh3 Br2.
W
Lithiation of 1,3-dithiane (3) was performed
according to the literature procedure,42) and THF was
1,3-dithiane at „15 to „109C, and the reaction mix-
freshly distilled from sodium benzophenone. All
ture was stored at the same temperature for 12 h. The
red color of the indicator vanished immediately while
adding the dibromide. The workup of the reaction
mixture was the same as that just described. 1e: NMR
W
reactions were carried out under a nitrogen at-
mosphere. Melting point (mp) data were recorded in
an open capillary and are uncorrected. The melting
points of linear alkanes 2 were measured with a
＝
5.4 Hz, CH3),
dH (CDCl3): 0.74 (3 H, doublet,
J
DuPont diŠerential scanning calorimeter from 20
9
C
1.06–1.83 (11 H, m, C
H
and C
H
2), 1.98 (2 H,
2
3
to 120 C at 0.5
9
9
C minute. 1H- and 13C-NMR spectra
doublet,
JHH 14.2 Hz,
quintet,
JHH 3.0),
＝
＝
W
were measured at 200 MHz (1H nucleus) and 50 MHz
(13C nucleus) in CDCl3 as the solvent, except as other-
wise noted. The chemical shifts of the new com-
pounds were assigned with 2D-NMR techniques as
far as possible. Elemental analyses were performed
by Atlantic Microlab, Inc. (Norcross, Georgia,
U.S.A.) or by the Microanalysis Laboratory of the
School of Chemistry at University of Illinois (Ur-
bana, Illinois, U.S.A.). Any deviation from the cal-
2.58–2.93 (8H, m, SCH2), 3.87 (2 H, triplet, J
＝
6.8 Hz, SC
H
S). NMR dC (CDCl3): 19.01 (CH3),
H), 32.51, 33.07, 47.45
S). IR nmax (KBr) cm„1: 2918, 1418, 1378, 1274,
1242, 1183, 907, 868, 777, 664. Anal. Found:; C,
52.19; H, 8.12; S, 39.78 . Calcd. for C14H26S4: C,
52.12; H, 8.12; S, 39.75
25.65, 30.05, 30.08, 31.87 (
(S
C
C
z
z
.
General procedure for the preparation of di-

Synthesis of Branched Long-chain Alkanes
529
alkylated
a
,
v
-bis(dithianyl)-alkanes
6
(Table 2 and
was re‰uxed for 20–30 min after each addition. The
solids were separated by ˆltration through warm Ce-
lite and rinsed thoroughly with 150 ml of warm cyclo-
hexane. The solvent was removed, and the desulfuri-
zation was repeated with an additional 7.0 g of Raney
nickel. The solvent was removed under reduced pres-
sure to yield a white solid that was recrystallized from
hexane or puriˆed by preparative TLC (SiO2,
hexane). 2a: IR nmax (KBr) cm„1: 2918, 2848, 1466,
3). Dithianes 1 were lithiated with butyllithium
(3 eq.) as already described at the temperature listed
in Table 2 („15 to „109C). Alkyl bromide 5 in an-
hydrous THF (5–10 ml) was added to a solution of 2-
lithio-1,3-dithiane at „15 to „10 C, and the mix-
ture was stored at „15 to „10 C for 12 h. The red
9
9
color of the indicator vanished shortly after adding
alkyl bromide 5. The workup of the reaction mixture
was the same as that already described. Monoalkylat-
1376, 722. Anal. Found: C, 85.42; H, 14.59
z
.
ed products. 7a: NMR
d
H (CDCl3): 0.89 (3 H, triplet,
Calcd. for C56H114: C, 85.40; H, 14.60 . 2g: NMR
z
＝
＝
J
6.0 Hz, C
2.11 (1 H, doublet, JHH 12.5 Hz, quintet,
2.71–2.98 (8 H, m, SC 2), 4.05 (1 H, triplet,
Hz, SC S). NMR dC (CDCl3): 14.08 (
23.99, 25.58, 25.97, 26.57, 29.18–29.78, 30.46,
H
3), 1.11–1.80 (65 H, m, alkyl-C 2),
H
dH (400 MHz, CDCl3): 0.85 (3 H, d,
J
6.4, C
3), 1,08 (1 H, m, C
2). NMR dC (100 MHz, CDCl3):
H3), 19.76 ( H3), 22.68, 27.13, 29.36,
29.60–29.80, 30.07, 31.95, 32.86 ( H), 37.19. IR nmax
(KBr) cm„1: 2919, 2849, 1472, 1464, 1377, 1274, 719.
Anal. Found: C, 85.37; H, 14.53 . Calcd. for
C40H82: C, 85.31; H, 14.69
H
3),
2
＝
＝
J
＝
J
3.5),
5.6
0.89 (6 H, triplet, J 6.8, C
1.26 (72 H, s, C
14.01 (
H
H
),
＝
H
H
H
C
H3), 22.65,
C
C
C
31.88, 35.43, 38.11, 47.64 (SCHS), 53.67 (SCS). IR
nmax (KBr) cm„1: 2920, 2850, 1464 (CH2 scissor),
z
1274, 718 (CH2 rocking). Anal. Found: C, 70.02; H,
z.
11.35; S, 18.54
11.45; S, 18.63
z
. Calcd. for C40H78S4: C, 69.92; H,
z
. 7g: NMR dH (CDCl3): 0.83 (3 H,
High-temperature gas chromatography of the syn-
thetic alkanes. High-temperature gas chromato-
graphic (HTGC) analyses were performed with a mo-
＝
＝
H3), 0.86 (3 H, double, J
triplet,
J
6.6 Hz, C
5.4 Hz, C
H
3), 1,14–1.98 (42 H, m), 2.09 (1 H,
2
＝
×
doublet, JHH 12.5 Hz, m), 2.71–2.93 (8 H, m,
SC 2), 3.98 (1 H, triplet, 6.6 Hz, SC S). NMR
C (CDCl3): 13.98 ( H3), 19.46 ( H3), 22.54, 23.84,
25.46, 25.88, 29.22–29.68, 30.37, 30.40, 30.60,
31.78, 32.72 ( H), 32.91, 33.51, 35.24, 37.98, 47.83,
53.28 (S
S). IR nmax (KBr) cm„1: 2918, 1458, 1376,
1274, 1240, 1179, 908, 868, 783, 721, 679. Anal.
Found: C, 65.85; H, 10.61; S, 23.36 . Calcd. for
C30H58S4: C, 65.89; H, 10.70; S, 23.41 Bisalkylat-
ed Products: 6a: NMR dH (CDCl3): 0.87 (6 H,
diˆed Chrompack WCOT-Ultimetal column (20 m
0.25 mm I.D., and 0.1 m phase thickness) equipped
H
J
＝
H
m
×
d
C
C
with a 1.5 m 0.55 mm I.D. deactivated stainless
steel retention gap. Each analysis was run on a
Hewlett-Packard model 5890 SII instrument
equipped for on-column sample injection. The initial
C
C
HTGC oven temperature was 134
sample solvent), with a 1.0-min. initial holding time,
then a temperature programmed at 10 C per min. to
450 C, and 5.0-min. ˆnal holding time. The carrier
gas was helium that had been passed through a series
of oxygen scrubbers. Reference -para‹ns (C40-C42,
9
C (for the o-xylene
z
z
.
9
9
＝
5.6 Hz, CH3), 1.13–1.60 (96 H, m,
``triplet'',
J
C
H
2), 1.78–2.06 (12 H, m), 2.80 (8 H, ``triplet'',
n
＝
J
6.2 Hz, SC
H
2). NMR dC (CDCl3): 14.11 (
H2), 26.00 (S
S). IR
C
H3),
H2),
C44, C46, C48, C50, C54, C56, C58 and C60) of gas chro-
matographic grade where purchased from Fluka
Chemical Corporation, Milwaukee, WI, U.S.A.
22.68, 24.04, 25.61 (dithiane
C
C
29.35–29.83, 31.91, 38.16, 53.40 (S
C
n
max (KBr)
cm„1: 2919, 2849, 1465 (CH2 scissor), 1404 (SCH2),
721 (CH2 rocking). Anal. Found: C, 74.72; H, 12.40;
Acknowledgments
S, 12.84
z
. Calcd. for C62H122S4: C, 74.79; H, 12.36;
. 6g: NMR dH (CDCl3): 0.83 (6 H,
6.6 Hz, C 3), 0.89 (3 H, doublet,
3), 1.12–1.49 (61 H, m), 1.72–1.97 (12 H,
m), 2.75 (8 H, ``triplet'', 5.6 Hz, SC 2). NMR dC
(CDCl3): 13.99 ( H3), 19.67 ( H3), 22.56, 23.91,
25.49, 25.90, 29.25–29.73, 30.74, 31.81, 33.20,
35.38, 38.01, 53.31 (SCS). IR
max (KBr) cm„1: 2915,
2849, 1471, 1377, 1272, 1238, 906, 715. Anal. Found:
S, 12.86
``triplet'',
z
J
H
We thank Chevron Petroleum Technology Com-
pany (La Habra, CA, U.S.A.) for funding this
project, and M. M. Pena for the HTGC analyses.
One of us, HJL, thanks Drs. D. S. Watt and M. S.
Meier for providing support and laboratory facilities.
＝
H
J
＝
5.6 Hz, C
J
＝
H
C
C
n
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