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_Adamantane _
By: George Simpson
The unique nature of diamond is heavily dependent upon its composition,
crystal structure, and mechanical, thermal, and electromagnetic properties.1
Of those dependencies, composition exacts the most influence over the
characteristics. Crystal structure is the repeating pattern of diamonds
composition, and each of the properties are the result of molecular
interaction which is determined by composition. Therefore, composition is
paramount in the determination of the qualities of diamond. Before its
discovery, adamantane was known as decaterpene, the name applied by Decker to
his tricyclic hydrocarbon. Decker believed that his decaterpene was similar in
structure as the diamond lattice. Decaterpene, as in diamond, was proposed by
Decker to be highly structured and strain free.2 Decker proposed decaterpene
in 1924, but that was all it was until 1933 when the structure was proven to
exist. Isolated in the petroleum of Hodinin, Czechoslovakia by Landa and
Machachaeck, decaterpene became incarnate.3 However, the fact that they found
the structure Decker predicted did not mean that his nomenclature would be
used to identify the compound. That honor was bestowed upon its discoverers
Landa and Machcahcaeck who used the Greek translation of diamond, adamantane,
to identify the compound.2 Crude petroleum is separated into its component
compounds by fractional distillation. The procedure involves a sample of the
petroleum to be heated until the sample is vaporized leaving behind any solid
impurities. The resulting steam enters a fractional distillation column in
which a temperature gradient had been instilled. The temperature of the column
decreases as the steam rises through the column. The idea is that, as the
temperature of the column decreases, the vapor temperature will decrease. When
the boiling point of a compound is passed, the compound will condense on the
sides of the column and be collected in the fraction well at that point. Thus
the mixture is separated into fractions of compounds with similar boiling
points in a mixture.4 Adamantanes high boiling point caused it to be one of
the initial compounds to condense with the kerosene fraction in the 190o C
cut.5 The only problem with the fractional distillation method is that
adamantane cannot be extracted in large quantities because it exists in only a
small quantity in petrol. The presence of adamantane was found to be only
0.0004% of the composition of petroleum by the fractional distillation
method.2 Adamantane is not alone in the petroleum distillate in which it is
present. Alkylated adamantane derivatives also show up in adamantane
containing distillate. (II, III, IV) The output of adamantane is capable of
being increased if the thiourea adduct method is employed on the petroleum.
Landa and Hale were able to isolate complexes of adamantane from crude
petroleum that had bonded to thiourea.5 Now that the natural product has been
discovered, the next logical step would be to formulate the natural process in
which the compound was made. As of 1964, the natural method that creates the
adamantane compound had not been found. The natural process that was attempted
was to bombard adamantane-free petroleum with catalysts in an attempt to
initiate the formation of adamantane. The resulting mixture was fractioned and
analyzed to see if any extra adamantane was created. In most cases, the
catalyst failed to produce any adamantane. However, many of the catalysts
produced derivatives that had the ring structure but with extra components
attached.5 The only catalyst shown to make a significant amount was AlCl3, but
not enough was created for the catalyst to be considered for mass production
of adamantane. Catalysts that failed were: oil-bearing stone from Hodin with
and without HF, aluminum silicate, aluminum oxide, concentrated sulfuric acid,
zinc chloride, iron(III) chloride, tin(IV) chloride, antimony(V) chloride.5 It
is believed that the reason many of the catalysts did not work, even though
they are present in natural petroleum, is that the conditions that they were
subjected to were experimental in nature. The creation of adamantane is
thought to be a biogenesis of petroleum under a set of conditions that is not
able to be recreated in the lab.2 With the natural mechanism a mystery, a
synthetic method to create the compound was sought after to allow the study of
adamantane to proceed. After all, with Landa in complete control of the slim
supply of adamantane, the cost of adamantane skyrocketed.6 Two methods were
investigated to be able to create the natural adamantane structure: ring
closure and isomerization. Before adamantane was known to the world, the
starting material commonly used to synthesize adamantane and its derivatives
through ring closure was being developed. In 1922, Meerwein was investigating
a way to remove the bridgehead carboxymethoxy group of ring compounds, and
reseal the ring structure with diiodomethane(V) and sodium. His experiments
failed because the malonic ester(VI) which he created forced the reactant
groups too far apart for the recycling to occur.3,4 Despite his failures,
Meerwein was able to inspire other advancements of his research through the
malonic ester which came to bear his name as Meerweins ester.7 This became
the common starting point for the search for the path to cyclic adamantane.
Bottger was the first to make great strides in the adamantane synthesis
research following Meerweins lead. Starting with Meerweins ester Bottger was
able to bring the ring together to create a cyclic product.6 The product was
of the tricyclo-[3.3.1.13,7] decane ring system of which adamantane is a
constituent, but Bottgers product still had external functional groups around
the ring instead of the only hydrogen around adamantane.5 As a result, what
Bottger had synthesized was not adamantane, but a derivative of itThe first
synthesis of true adamantane did not occur until 1937 when Prelog and Seiworth
were able to advance the work of Bottger, and decarboxylize the ring structure
leaving behind only the basic ring.6 Adamantane was their final product, but
that product still was not produced in large quantities. The system used by
Prelog and Seiworth yielded an output of adamantane at 0.16% of the materials
going into it.7 As often occurs in science, the advancements made by Prelog
and Seiworth were furthered by the research of others. Landa reentered the
adamantane research realm with Stetter. Together, they were able to improve
the efficiency of Prelog and Seiworths overall synthesis. Decarboxylation
yield was increased by the addition of the Heinsdecker pathway (11%), and the
Hoffman reaction (24%). Even with the advancements, synthesis of adamantane by
ring closure was never able to yield an output over 6.5% of the reactants.5
Nevertheless, the process developed by Bottger remained an efficient method
for the synthesis of derivatives. This left research of adamantane to be
inferred through the experimentation of adamantanes derivatives since its
synthesis was not economical. This was true until 1957 when Paul von R.
Schleyer accidentally synthesized adamantane. Schleyer was working on the
inversion of reversible endo-exo isomerization of
tetrahydrodicyclopentadiene.3 During his experimentation, he noticed that the
reaction had a side product of a white crystalline compound. The compound was
set aside and investigated later. The mysterious compound was found to have a
melting point that matched the experimental adamantane melting point. Other
adamantane-like characteristics later solidified his compound as a match.
Schleyers discovery of an isomerization method of adamantane synthesis rocked
the scientific community, as it provided a more efficient method for
adamantane production. Schleyer was able to increase the output of his
adamantane synthesis to a 30% and 40% yield by exposing the
tetrahydrodicyclopentadiene to an AlCl3-HCl mixture under 40 atms. of pressure
of hydrogen and HF-BF3 catalyst respectively.7 When Schleyer focused his
procedure on the retrieval of adamantane, he found that the synthesis was
bountiful with the starting reactant dicyclopentadiene which is a common
compound.3 Research into the enigmatic compound could then proceeded full
force from this point on to examine the compound to its every minute detail.
What they found confirmed their previous assertions that adamantane was unlike
any carbohydrate known to man. That carbohydrate was found to be a three fused
chairs of cyclohexane rings bound only to hydrogen atoms. The crystallized
structure of adamantane was studied in depth by X-ray diffraction. An X-ray
diffraction pattern is created through the interaction of photons emitted from
an excited metal atom with the crystal form of a compound. The photon either
misses the crystal atoms or is deflected by the atom. Most photons miss the
atoms, but those deflected do so in a regular pattern because of the
repetitious nature of crystals. That pattern may be recorded through the use
of a strip of photographic film or a two-dimensional array detector to provide
a hard copy of the deflection pattern.8 Thus the crystalline lattice type,
distance between atoms, and number of atoms per unit cell may be found by
analysis of the diffraction pattern. The crystal orientation is a face
centered cubic lattice that was completely separate from all known
carbohydrate crystal orientation.6 Face centered cubic means that there are
atoms centered at the faces of the cube as well as at the corners. Adamantane
was derived to have a tetragonal space group with four molecules per unit
cell, and the vector quantities a = 6.60A and c = 8.81A.7 The carbon bond
lengths and angles were stereotypically sound as they were measured to be 1.54
_ 0.01A and 109.5 _ 1.5o respectively.6 This data showed proof that adamantane
was a stable compound, but how stable they did not know until the physical
qualities were determined. The melting point was determined by sealed tube,
and was found to be 269oC which is the melting point for adamantane exposed to
the atmosphere as well as the highest melting point for a carbohydrate.9 It is
unusual for such an occurrence, but adamantane has no end to its surprises.
The exact boiling point of adamantane is impossible to be determined for it is
incapable of being reached except by mixture with other carbohydrates at which
time the boiling point is 190oC. It is this property that allowed adamantane
to be discovered by fractionalization.6 The enigmatic nature of adamantane is
reinforced by the fact that it has such a high melting and boiling point, yet
it remains true that adamantane will sublime at room temperature and
atmospheric pressure. Now that adamantanes crysatlline structure is known
along with the physical properties, what remains is for technology to fill in
the blanks as far as molecular interactions of the compound. Adamantane was
subjected to NMR and IR(Fig 1,2) Each test produced results that were unique
for any carbohydrate upon which the same conditions were exerted.5 The most
probable reason for such unique results is the symmetrical nature of
adamantane. In fact, adamantane has a symmetry number of twelve which is
unheard of in a carbohydrate. This means that throughout the structure there
exists a combination of planes and axes about which adamantane is symmetrical
or identical that totals twelve. Many compounds, organic and inorganic, are
symmetrical in one or two dimensions, but few are symmetrical in three
dimensions as adamantane is. NMR uses the magnetic nature of atom nuclei to
its advantage. By surrounding a compound in a magnetic field, the nuclei
become vulnerable to excitation by radiation in the radiofrequency range. The
radiofrequency that the nuclei absorb is dependent upon the environment the
nuclei are exposed to as far as the neighboring nuclei and those the nuclei
are bonded to.10 In this case, a proton NMR showed adamantane as only a sharp
doublet with a spacing of 0.95 ppm.(Fig 1) The symmetry of adamantane is
perfectly supported by these NMR results because only a doublet means that all
of the protons are identical in nature. This shows that each proton in the
structure of adamantane is sharing each of the electrons equally creating a
strong dependence of resonance by all protons.6 The singularity in the NMR
result becomes an important diagnostic tool for determination of the purity of
an adamantane perspective. Any substitution anywhere on the ring would
unbalance resonance of the compound that would be picked up by the NMR in the
form of another series of peaks indicating an adamantane derivative as long as
the doublet remains present. IR results are much the same as those of NMR in
that adamantane itself gives a clear result while any impurity clouds those
results. Specifically, adamantane gives a major doublet in the region of 2926
cm-1 with a 0.8983 transmittance, and other peaks shown on Figure 2. This
means that around the adamantane compound exists methyl groups that are
similar in nature and surrounding environment. Consequently, all bonds absorb
the same wavelengths that suggests identical motion of each of the bonds
whether that be stretching, scissoring, or other. Any variance in a functional
group would result in the absorbance wavelength to change. Therefore, an
increase in the number of peaks and a decrease in intensity of the existing
peaks would occur because the change in bonding pattern would limit or expand
the possible motions of the bonds. Each bond-motion type absorbs a different
wavelength in the IR, so any change in the types changes the absorbances. IR
translates the amount transmitted per wavelength to an electrical signal that
is interpreted through fourier transform to an IR spectrogram.10 Absorbance is
the inverse of transmittance, so any change in absorbance changes the
transmittance and the ending spectrogram values. Since adamantane is so
symmetrical and stable, it becomes the perfect basis for many studies and
research. In fact the universality of adamantane is so great that it is
capable of being used for: structure reactivity relationships, development of
empirical force field methods, orientation disorder probe model, and structure
basis for drugs.5 The possibilities are endless for adamantane and its uses
simply because of its simplicity in nature and structure allow for a structure
that is one of the most unique and strong in nature.
_Bibliography _
Resources 1. M. Shen, H.F. Schaeffer III, C. Liang, J. Lii, N.L. Allinger, and
P.v.R. Schleyer. J. Am. Chem., 114, 497 (1992) 2. B. J. Mair, M. Shainenger,
N.C. Krouskov, and F.D. Rossini, Anal. Chem., 31, 2082 (1959) 3. P. von Rague
Schleyer, J. Am. Chem. Soc., 79, 3292 (1957) 4. R.M. Roberts, J.C. Gilbert,
S.F. Martin. Experimental Organic Chemistry. Harcourt Brace College
Publishers: Philadelphia, PA. 1994. 5. M. A. McKervey, Tetrahedron, 36, 971
(1980) 6. R. C. Fort, and P. von Rogue Schleyer, Chem. Rev., 64, 277 (1964) 7.
S. Coffey, ed. Rodds Chemistry of Carbon Compounds. Vol 2. Part C. Elsevier
Publishing Co.: New York. 1969. 8. D.A. McQuarrie, J.D. Simon. Phhysical
Chemistry: A Molecular Approach. University Science Books: Sausalito, CA.
1997. 9. Adamantane. Dictionary of Organic Compounds. Vol 1. 5th ed.,
Buckingham, J. ed. Chapman and Hall: New York. 1982. 10. Ege, Seyhan. Organic
Chemistry: Structure and Reactivity. 3rd ed. D.C. Heath and Co.: Lexington,
MA. 1994.
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