Synthesis of diamantane via skeletal isomerization of hydrogenated cyclohepta-1,3,5-triene dimers in ionic liquid [Et3NH]+ [Al2Cl7]–

Article abstract of DOI:10.1134/S107042801712017X

Diamantane was synthesized in 91–97% yield by skeletal isomerization of a mixture of hydrogenated cyclohepta-1,3,5-triene dimers, pentacyclo[8.4.0.0^3,7.0^4,14.0^6,11]tetradecane and pentacyclo-[7.5.0.0^2,8.0^5,14.0^7,11]tetradecane, at a ratio of 3: 2 in the presence of ionic liquid [Et₃NH]⁺ [Al₂Cl₇]^–.

Full text of DOI:10.1134/S107042801712017X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2017, Vol. 53, No. 12, pp. 1881–1883. © Pleiades Publishing, Ltd., 2017.
Original Russian Text © R.I. Aminov, R.I. Khusnutdinov, 2017, published in Zhurnal Organicheskoi Khimii, 2017, Vol. 53, No. 12, pp. 1845–1847.
SHORT
COMMUNICATIONS
Synthesis of Diamantane via Skeletal Isomerization
of Hydrogenated Cyclohepta-1,3,5-triene Dimers
in Ionic Liquid [Et3NH]+ [Al2Cl7]–
R. I. Aminov* and R. I. Khusnutdinov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
*e-mail: inklab4@gmail.com
Received July 12, 2017
Abstract—Diamantane was synthesized in 91–97% yield by skeletal isomerization of a mixture of hydro-
genated cyclohepta-1,3,5-triene dimers, pentacyclo[8.4.0.03,7.04,14.06,11]tetradecane and pentacyclo-
[7.5.0.02,8.05,14.07,11]tetradecane, at a ratio of 3:2 in the presence of ionic liquid [Et3NH]+ [Al2Cl7]–.
DOI: 10.1134/S107042801712017X
Diamantane (1) is the second member of the homo-
logous series of diamond-like hydrocarbons (adaman-
tanoids). It is used in the synthesis of heat-resistant
synthetic lubricating oils (e.g., cable oil) or their
components, solvent-resistant polymeric materials and
rubbers, and medicinal agents [1–4].
[7.5.0.02,8.05,14.07,11]tetradecane (2b) [8]. The isomer-
ization of 2a and 2b to diamantane (1) was accom-
plished in the presence of AlCl3 at a ratio of 4.8:1 on
heating in boiling methylene chloride for 12 h.
Inorganic ionic liquids are unique subjects of
chemical studies; since the end of the XX century, they
have been widely used in catalysis and organic
synthesis. Inorganic ionic liquids exhibit properties of
Brønsted or Lewis acids, as well as superacidic prop-
erties. In particular, superacidic properties are intrinsic
to melts containing aluminum chloride, which makes
them attractive for use as catalysts [9]. For example,
the ionic liquid [Et3NH]+ [Al2Cl7]– showed a high cata-
lytic activity in the isomerization of cyclohexane to
methylcyclopentane [10].
The most widely known method of synthesis of
diamantane (1) is based on skeletal isomerization of
C14H20 hydrocarbons resulting from hydrogenation of
heptacyclic norbornadiene dimer Binor-S. The yield of
diamantane (1) in the isomerization of tetrahydro-
Binor-S in the presence of CS2–AlBr3 [5], superacid
catalysts B(OSO2CF3)3, CF3SO3H–SbF5, and
CF3SO3H–B(OSO2CF3)3 [6], and Na-Y zeolite [7] was
60–98%. Diamantane was also obtained in 89% yield
by skeletal isomerization of individual hydrogenated
cyclohepta-1,3,5-triene dimers, pentacyclo-
[8.4.0.03,7.04,14.06,11]tetradecane (2a) and pentacyclo-
We have found that [Et3NH]+ [Al2Cl7]– efficiently
catalyzes the isomerization of a 3:2 mixture of penta-
cyclo[8.4.0.03,7.04,14.06,11]tetradecane (2a) and penta-
Ti(acac)2Cl2–Et2AlCl
40°C, 6 h
H2, Pd/C, 20°C, 6 h
+
+
3a
3b
2a
2b
[Et3NH]+[Al2Cl7]–
1
1881

AMINOV, KHUSNUTDINOV
1882
(C2, C5), 26.04 (C9, C12), 22.03 (C8, C13). Mass spec-
trum, m/z (Irel, %): 188 (30) [M]+, 145 (28), 131
(35), 117 (26), 105 (32), 95 (38), 91 (89), 79 (100), 67
(46), 41 (43).
Synthesis of diamantane (1) by skeletal isomerization of
a 3: 2 mixture of pentacyclo[8.4.0.03,7.04,14.06,11]tetradecane
(2a) and pentacyclo[7.5.0.02,8.05,14.07,11]tetradecane (2b)
Molar ratio (2a+2b)/ Tempera- Time, Conver- Yield
Pentacyclo[7.5.0.02,8.05,14.07,11]tetradecane (2b).
13C NMR spectrum (CDCl3), δC, ppm: 51.34 (C1),
50.96 (C8), 43.12 (C7), 43.01 (C9), 41.38 (C14), 41.02
(C2), 35.86 (C11), 35.78 (C5), 31.33 (C10), 31.30 (C6),
25.43 (C12), 25.12 (C13), 24.17 (C4), 23.91 (C3). Mass
spectrum, m/z (Irel, %): 188 (100) [M]+, 173 (16), 117
(24), 92 (30), 91 (47), 79 (40), 67 (17), 41 (20).
ionic liquid
ture, °C
h
sion, % of 1, %
3:1a
2:1a
1:1a
1:1a
1:2
1:2
1:2
1:2
1:2
50
50
50
80
50
50
50
80
20
08
08
08
08
08
04
05
02
40
012
053
091
079
100
094
100
100
100
12
53
91
79
93
94
97
97
95
Diamantane (1). A 50-mL glass reactor was
charged under argon with 0.3 g (1 mmol) of isomer
mixture 2a/2b and 1.29 g (2 mmol) of preliminarily
prepared [Et3NH]+ [Al2Cl7]– [12]. The mixture was
stirred for 5 h at 50°C, cooled to room temperature,
and extracted with petroleum ether. The extract was
filtered through a layer of silica gel, the sorbent was
washed with petroleum ether, the solvent was distilled
off, and the residue was recrystallized from ethyl
acetate–cyclohexane (1:1). Yield 0.291 g (97%), white
crystals, mp 244–245°C. 13C NMR spectrum (CDCl3),
δC, ppm: 37.76 (C1, C2, C6, C7, C11, C12), 38.51 (C3, C5,
C8, C10, C13, C14), 26.18 (C4, C9). Mass spectrum, m/z
(Irel, %): 188 (100) [M]+, 160 (5), 159 (10), 145 (8),
131 (13), 130 (18), 120 (7), 105 (15), 91 (28), 79 (25),
67 (15). Found, %: C 88.75; H 11.25. C14H20. Cal-
culated, %: C 88.29; H 10.71.
a
In cyclohexane.
cyclo[7.5.0.02,8.05,14.07,11]tetradecane (2b) to diaman-
tane (1) in up to 97% yield. Hydrocarbon mixture
2a/2b was obtained by cyclodimerization of cyclo-
hepta-1,3,5-triene (6 h) [11], followed by hydrogena-
tion of dimer mixture 3a/3b (3:2) over Pd/C at room
temperature. The best yield of 1 was achieved at
a molar ratio of mixture 2a/2b and the ionic liquid of
1 :2. Depending on the reaction time (2–40 h) and
temperature (20–80°C), the yield of 1 varied from 93
to 97%. When the ratio of 2a/2b to [Et3NH]+ [Al2Cl7]–
ranged from 1:1 to 3:1, the conversion decreased to
12% (see table); these ratios required the use of
cyclohexane as solvent.
Thus, the ionic liquid [Et3NH]+ [Al2Cl7]– is an ef-
ficient catalyst for the isomerization of a 3:2 mixture
of pentacyclo[8.4.0.03,7.04,14.06,11]tetradecane (2a) and
pentacyclo[7.5.0.02,8.05,14.07,11]tetradecane (2b) to
diamantane (1).
1
The H and 13C NMR spectra were measured on
a Bruker Avance III-500 spectrometer at 500 and
125 MHz, respectively, using CDCl3 as solvent; the
chemical shifts are given relative to tetramethylsilane.
The mass spectra were obtained on a Shimadzu
GCMS-QP2010 Plus instrument (SPB-5 capillary
column, 30 m×0.25 mm; carrier gas helium, oven
temperature programming from 40 to 300°C at a rate
of 8 deg/min; injector temperature 280°C, ion source
temperature 200°C; electron impact, 70 eV). Chro-
matographic analysis was performed on Shimadzu
GC-9A and GC-2014 instruments (2 m × 3-mm
column packed with 5% SE-30 on Chromaton N-AW-
HMDS, oven temperature programming from 50 to
270°C at a rate of 8 deg/min; carried gas helium, flow
rate 47 mL/min).
Isomer mixture 2a/2b. A glass reactor was charged
with 0.5 g of Pd/C, 5 g of a 3:2 mixture of pentacyclo-
[8.4.0.03,7.04,14.06,11]tetradeca-8,12-diene (3a) and
pentacyclo[7.5.0.02,8.05,14.07,11]tetradeca-3,12-diene
(3b), and 15 mL of hexane, and hydrogen was supplied
at a pressure of 1 atm at room temperature. When the
reaction was complete, the mixture was filtered
through a layer of silica gel, the sorbent was washed
with hexane, and the solvent was distilled off. Yield
4.9 g (98%), isomer ratio 2a/2b 3:2.
Cyclohepta-1,3,5-triene, triethylamine hydro-
chloride, cyclohexane, AlCl3, and 10% Pd/C were
commercial products.
Pentacyclo[8.4.0.03,7.04,14.06,11]tetradecane (2a).
13C NMR spectrum (CDCl3), δC, ppm: 46.88 (C1, C6),
41.85 (C7, C14), 41.52 (C3, C4), 34.42 (C10, C11), 32.52
The structural studies were performed using unique
equipment of the Agidel Joint Regional Center.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 53 No. 12 2017

SYNTHESIS OF DIAMANTANE VIA SKELETAL ISOMERIZATION
1883
7. Dzhemilev, U.M., Khusnutdinov, R.I., Kislitsina, K.S.,
Kutepov, B.I., Khazipova, A.N., and Travkina, O.S.,
RU Patent no. 2459794, 2011; Byull. Izobret., no. 24.
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