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Adamantane

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Adamantane


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 diamond's 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 Adamantane's 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 Meerwein's 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 Meerwein's lead. Starting with Meerwein's 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 Bottger's 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 it.

The 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 Seiworth's 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 adamantane's derivatives since it's 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.

Schleyer's 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 ...

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Keywords: adamantane structure, adamantane carboxylic acid, adamantane drugs, adamantane derivatives, adamantane uses, adamantane synthesis, adamantane point group, adamantane nmr

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