Synthesis and Thermodynamic properties of 2-Adamantanone

2‑Adamantanone is a white to off‑white crystalline solid with a camphor‑like odor under standard conditions. It is mainly used in the synthesis of active compounds and photosensitive materials, and has demonstrated notable utility in the preparation of adamantane‑based bioactive molecules and functional organic derivatives. The synthesis of 2‑adamantanone can proceed via oxidation of 2‑adamantanol or directly from adamantane through mixed‑acid oxidation using concentrated sulfuric acid and p‑toluenesulfonic acid.

Figure1: Picture of 2‑adamantanone

Synthesis

Method 1

Researchers have reported an efficient preparation route for 2‑adamantanone starting from adamantane. The process employs a mixed‑acid system (concentrated sulfuric acid/p‑toluenesulfonic acid) to oxidize adamantane, followed by crystallization from an alcohol‑water mixture, purification with sodium bisulfite, acid hydrolysis, and extraction. This approach avoids steam distillation, thereby reducing energy consumption and improving operational efficiency. The method affords 2‑adamantanone with a yield exceeding 65% and a purity higher than 99.8%, making it suitable for industrial‑scale production. [1]

Method 2

An alternative synthesis and extraction procedure for 2‑adamantanone has also been disclosed. In this process, adamantane or 1‑adamantanol is first mixed with concentrated sulfuric acid in a feeding tank and then pumped into a micro‑tube reactor, where oxidation is carried out at 80–120 °C for 30 seconds to 2 minutes. The reaction mixture is subsequently diluted with water to lower the sulfuric acid concentration to 65–78%, which suppresses its oxidizing capacity while maintaining sufficient acidity. An organic solvent such as petroleum ether is added to extract any unreacted starting material, leaving the sulfate ester of 2‑adamantanol in the acidic aqueous phase. The separated organic phase is distilled and cooled to recover the starting material. The acidic phase is further diluted to 40–55% to hydrolyze the intermediate, yielding 2‑adamantanone, which is then extracted with an organic solvent such as toluene. The organic extract is concentrated and crystallized to obtain pure 2‑adamantanone. The remaining acid phase is filtered, concentrated under reduced pressure to 60–70% sulfuric acid, and recycled. This route offers simplified operation, facilitates the recovery and reuse of concentrated sulfuric acid, and provides a high yield of the target product. [2]

Thermodynamic properties

The results of a comprehensive study of thermodynamic properties of 2-adamantanone in different phase states are reported. The heat capacity of the compound in the condensed state was measured from 5 to 310K with an adiabatic calorimeter and between 290 and 610K with a differential scanning calorimeter of the heat-bridge type. Adamantanone undergoes a solid-to-solid phase transition at 216.4±0.1K with trsH◦ m = 7.627 ± 0.014kJmol−1 and fusion at 557.5±0.2K with fusH◦ m = 11.77 ±0.24kJmol−1. The solid-phase transition is associated with formation of orientationally disordered (plastic) crystal. The thermodynamic functions of the compound in the crystalline and liquid states were obtained. The saturated vapor pressure of crystalline adamantanone between 280 and 333 K was measured using the Knudsen effusion method, accounting for vapor undersaturation in the effusion cell. The sublimation enthalpy of the compound was measured with a differential Calvet type calorimeter. The weighted average value of the sublimation enthalpy was subH◦ m (298.15K) = 66.38 ± 0.25kJmol−1. The thermodynamic properties of the compound in the ideal gaseous state were calculated by statistical thermodynamics. A comprehensive thermodynamic investigation of 2‑adamantanone across its various phase states was conducted. Notably, the strong consistency observed among the data obtained from different methodologies and techniques underscores their reliability. Calorimetric analysis confirmed the formation of an orientationally disordered crystal by this compound. Further exploration of the plastic crystalline phase of 2‑adamantanone is expected to provide deeper insights into the nature of molecular disorder in organic crystals. [3]

Baeyer-Villiger oxidation

In a Baeyer-Villiger oxidation study, researchers employed SnCl₂·2H₂O as the catalyst and 30 wt% H₂O₂ as the oxidant to convert 2‑adamantanone into the corresponding lactone with 100% selectivity. The product was isolated by column chromatography and characterized by NMR. The effects of solvent, reaction temperature, catalyst loading, and reaction time on the catalytic activity and product selectivity were systematically investigated, and a preliminary reaction mechanism for this catalytic oxidation system was discussed. [4]

References

[1] F. Jinyin, P. Zhaoxi, An Efficient Preparation Method for 2-Adamantanone, Chinese Patent CN202210869169.5.

[2] W. Nan,  A Synthesis and Extraction Method for Adamantanone, Chinese Patent CN202010161036.3.

[3] A. B. Bazyleva, A. V. Blokhin, G. J. Kabo et al., Thermodynamic properties of 2-Adamantanone in the condensed and ideal gaseous states, Thermochimica Acta, 2006, 451: 65-72.

[4] J.Q. Wang, R. R. Wang, C. L. Li et al., Journal of Northwest Normal University (Natural Science Edition), 2007, 43: 4.

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