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Diamonds from Crude Oil.

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Diamondoid Hydrocarbons
Diamonds from Crude Oil?
Henning Hopf*
cage compounds · diamondoids · hydrocarbons ·
eventy years ago Landa and co-workers isolated a crystalline hydrocarbon in
minute amounts (0.0004 %) from a sample of petroleum collected near the
village of Hodon n in Moravia.[1] The
structure of the compound (3,
Scheme 1), which they named adaman-
Scheme 1. The Schleyer route to adamantane
tane, was proposed by Lukes on the
basis of its unusual physical properties
and by applying the then new technique
of X-ray structural analysis.[1] It was
several years before Prelog and Seiwerth reported the first synthesis of this
cage hydrocarbon; their multistep route
never provided more than mg amounts,
and the total yield was not more than
0.3 %.[2] Although later work by Stetter
[*] Prof. Dr. H. Hopf
Universit$t Braunschweig
Institut f'r Organische Chemie
Hagenring 30
38106 Braunschweig (Germany)
Fax: (+ 49) 531-391-5388
and co-workers improved the situation
significantly—now 200-mg batches
could be prepared and the total yield
of the adamantane synthesis was increased to 6 %[3]—adamantane remained a rare and precious compound,
the chemical properties of which could
not be studied on a broader scale
because of lack of material.
This situation changed dramatically
when—in 1957—Schleyer reported on a
discovery he had made while trying to
isomerize endo-tetrahydrodicyclopentadiene (1) to its exo isomer 2. When the
easily available 1 was refluxed overnight
in the presence of aluminum trichloride
the intended isomerization did indeed
take place, but the process was accompanied by a surprising further
rearrangement yielding adamantane[4]
(Scheme 1). Over the years the Schleyer
route was improved and made into a
technical process, and currently 100 g of
analytically pure 3 cost a modest 35 Euros.
Hundreds of adamantane derivatives have been prepared since then
and many of them are also available
from commercial suppliers at reasonable prices. A particular prominent derivate is 1-amino adamantane (4) or
Symmetrel which is used to treat Parkinson and related syndromes and as an
antiviral agent against Type A influenza
in humans.
The name adamantane is derived
from the Greek word for diamond
(adamas),[5] a telling description since
the carbon framework of 3 is superimposible on the diamond lattice.[6]
Formally the latter can be built up by
succesively fusing adamantane building
blocks, and the intermediate hydrocarbons formed en route are known as
diamondoids (see below). The first two
“adamantanalogues” of 3 hence contain
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/anie.200301631
two (diamantane, 5) and three facefused cages (triamantane, 6, Scheme 2).
From tetramantane on, the structural complexity of the diamondoids begins
Scheme 2. Diamondoids as hydrocarbons with
a carbon framework that is superimposable
on the diamond lattice.
to increase: for this polycyclic hydrocarbon four isomers are possible and it is
the first unsubstituted diamondoid exhibiting chirality. With the pentamantanes the situation is even more complex: there are nine isomers with the
formula C26H32 and a molecular weight
(Mw) of 344 and one C25H30 isomer with
Mw 330.[7] There are 39 hexamantanes,
28 of which are C30H36 isomers, 10 are
C29H34 hydrocarbons, and one, the pericondensed hexamantane described below, also known as cyclohexamantane, is
a C26H30 compound. With octamantane
the number of possible (chiral and
achiral) isomers has exploded to several
hundred which are distributed over five
molecular weight classes. For example,
the octamantane class with the formula
C34H38 and a Mw of 446 includes 18
isomeric structures.
The degree of difficulty of synthesizing the higher diamondoids parallels the
Angew. Chem. Int. Ed. 2003, 42, 2000 – 2002
undecamantane were separated and
identified) provided single crystals of
X-ray quality; Figures 1 and 2 show a
selection of the resulting structures.
Rod-shaped hydrocarbons such as
[1212]pentamantane (11)[7] are characterized by long axes perpendicular to
their diamond (110) lattice planes. Increasing the length of such a molecular
rod by a further adamantane cage increases the length of the rod by 0.10 to
0.15 nm. [1213]Pentamantane (14) occurs in the form of two helical enan-
Scheme 3. Directed syntheses of several simple diamondoids.
structural complexity, of course, and the
higher members of the series are inaccessible by directed routes. For example,
whereas for both di- (5) and triamantane
(6) several methods of preparation, a
selection of which is shown in Scheme 3
and which are all based on the Schleyer
Lewis acid catalyzed isomerization
process, have been reported (7!5,[8]
8!6[9]), the synthesis of anti-tetramantane (10) by McKervey and co-workers
was much more involved and relied on
the availability of a diamondoid precursor, the dibromide 9, which was converted into 10 in a multistep sequence
involving a double homologation.[10] The
other isomers of 10 were unknown until
very recently, as were any of their higher
Up to now the largest member of the
diamondoid series isolated from petroleum was diamantane. Recently, however, R. M. K. Carlson and co-workers,
discovered that higher analogues, from
tetra- to at least undecamantane, also
occur in petroleum samples obtained
from Gulf of Mexico and Western
Canada Basin oil wells.[11] By vacuum
distillation above 345 8C higher diamondoid-containing fractions were first
obtained, from which non-diamondoid
hydrocarbons were removed by pyrolyAngew. Chem. Int. Ed. 2003, 42, 2000 – 2002
sis at 400–450 8C, the desired polycyclic
compounds possessing the higher thermodynamic stability. Aromatic and polar components were then removed by
argentic silica gel column chromatography and the desired diamondoids finally
isolated by RP-HPLC on octadecylsilane (RP18) columns and shape-selective Hypercarb HPLC columns. The
separated and purified higher diamondoids were recrystallized from acetone
and subjected to spectroscopic and mass
spectrometric analysis.
Many of the numerous new hydrocarbons (all four tetramantanes, nine
pentamantanes, one hexa-, two hepta-,
and two octa- as well as one nona- to
Figure 1. The structures of several pentamantanes in the crystal: [1212]pentamantane (11),
[1(2,3)4]pentamantane (12), [12(3)4]penta
mantane (13), [1213]pentamantane (14).
Figure 2. Structures of a hexa- and a heptamantane as well as the methyl derivative of a pentamantane in the crystal: [121312]hexamantane (15), [121321]heptamantane (16), 3-methyl[1(2,3)4]pentamantane (17).
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
tiomers; by chromatography on cyclodextrin phases these screw-shaped molecules could indeed by separated.
Another type of geometry is illustrated by [121312]hexamantane (15).
This recently isolated and characterized
diamondoid,[12] which displays beautiful
transparent crystals with a pronounced
luster, is a disc-shaped molecule like its
higher analogue [121321]heptamantane
(16). Regarding 15 as a “jewel”, it may
be thought of as a nanometer-sized
diamond of 1020 carat (1 carat = 0.2 g).
That not all of these new polycyclic
hydrocarbons are parent systems is
demonstrated by 3-methyl-[1(2,3)4]pentamantane (17). The question of derivatization has, in fact, been addressed by
Dahl et al. already, and they have prepared many functionalized higher diamondoids (including bromo, hydroxy,
amino, oxa, and aza derivatives): although the concentration of the starting
materials in the crude oil fractions is
only in the 1–100 ppm range, apparently
enough material was available for “real”
preparative chemical work.
As far as the mechanism of formation of the new diamondoids in the
geosphere is concerned, one can only
speculate at present. Dahl et al. suggest
a process derived from the mechanism
proposed for Schleyer's 1!3 intercon-
version and which could involve cationic
intermediates.[13] These could be produced from double bonds still present in
newly generated petroleum by interaction with superacidic sites on naturally
occurring clay minerals in petroleum
source rocks. The astronomically high
number of different pathways available
for these rearrangements—2897 alternatives have been suggested for the
original Schleyer process[13]—could explain the low concentration of the new
diamondoids in petroleum and the presumably geological reaction times, the
now isolated structures representing the
global minima at the end of a several
million-year-long chemical journey.
[1] S. Landa, Chem. Listy 1933, 27, 415; cf.
S. Landa, S. Hala, Collect. Czech. Chem.
Commun. 1959, 24, 93 – 98, and references therein. The structure determination
of 3 is mentioned in these references and
in reference [2]
[2] V. Prelog, R. Seiwerth, Ber. Dtsch.
Chem. Ges. 1941, 74, 1644 – 1648.
[3] H. Stetter, O.-E. BJnder, W. Neumann,
Chem. Ber. 1956, 89, 1922 – 1926.
[4] P. von R. Schleyer, J. Am. Chem. Soc.
1957, 79, 3292.
[5] The chemistry of adamantane has been
reviewed many times. For a recent
collection of references see: H. Hopf,
Classics in Hydrocarbon Chemistry, Wi-
2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ley-VCH, Weinheim, 2000, chap. 3,
pp. 23–30.
The structure of the diamond lattice has
been known since the early 20th century: W. H. Bragg, W. L. Bragg, Nature
1913, 91, 554.
For the nomenclature of the higher
diamondoid hydrocarbons see: A. T.
Balaban, P. von R. Schleyer, Tetrahedron, 1978, 34, 3599 – 3609.
C. A. Cupas, P. von R. Schleyer, D. J.
Trecker, J. Am. Chem. Soc. 1965, 87,
917 – 918.
M. A. McKervey, Chem. Soc. Rev. 1974,
3, 479 – 512, and references therein;
G. A. Olah in Cage Hydrocarbons
(Ed.: G. A. Olah), Wiley, New York,
1990, pp. 103 – 153.
W. Burns, T. R. B. Mitchell, M. A.
McKervey, J. J. Rooney, G. Ferguson, P.
Roberts, J. Chem. Soc. Chem. Commun.
1976, 893 – 895; cf. M. A. McKervey,
Tetrahedron 1980, 36, 971 – 992.
J. E. Dahl, S. G. Liu, R. M. K. Carlson,
Science 2003, 299, 96 – 99.
J. E. P. Dahl, J. M. Moldowan, T. M.
Peakman, J. Clardy, E. Lobkovsky,
M. M. Olmstead, P. W. May, T. J. Davis,
J. W. Steeds, K. E. Peters, A. Pepper, A.
Ekuan, R. M. K. Carlson, Angew. Chem.
2003, 115, 2086 – 2090; Angew. Chem.
Int. Ed. 2003, 42, 2040 – 2044.
H. W. Whitlock, Jr., M. W. Siefken, J.
Am. Chem. Soc. 1968, 90, 4929 – 4939.
Angew. Chem. Int. Ed. 2003, 42, 2000 – 2002
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