Thermodynamic properties of 1-aminoadamantane
Introduction
The compound 1-aminoadamantane is an intermediate compound and an effective base for drugs on the basis of 1-aminoadamantane hydrochloride (trade names – amantadine, midantan, and symmetrel), which is used for the prevention and the early-stage treatment of influenza A [1], [2]. It was shown that the medication also exhibited a dopaminergic neurotransmission, which is the reason it is often applied in medical practice for treatment of dementia, Parkinson’s and Alzheimer’s diseases, stroke, hypoxic brain afflictions, neuroinfections, etc. [1], [3]. At present, amantadine in combination with other preparations is being intensively studied as a cure for hepatitis C in those cases where other methods are inefficient [4], [5].
This multiple use of amantadine creates a special interest in the study of its physiological activity as well as of efficient technologies of its production. The latter requires a large set of thermodynamic data for all components of a technological scheme under study. In spite of the long-term application of the medication, there has not been any investigation of physicochemical properties for amantadine and its effective base – 1-aminoadamantane. The absence of thermodynamic data for the latter is probably due to the particular difficulty and complexity in studying this extremely reactive amine. For example, its high reactivity can be illustrated by the following: when exposed to the open air, the compound absorbs water vapours and carbon dioxide up to (0.5 to 2) · 10−2 mass fraction per 10 min (depending on the crystal size) with the formation of 1-aminoadamantane carbonate or/and 1-aminoadamantane hydrogen carbonate. This indicates that if accurate data on its thermodynamic properties are needed, any contact by the compound with the air must be avoided.
The present work summarizes the results of a comprehensive study of thermodynamic properties of 1-aminoadamantane, the basic form of amantadine, in different phases. It also includes a thermodynamic analysis of its synthesis from 1-adamantanol.
Section snippets
Sample preparation
A commercial sample of 1-aminoadamantane (Aldrich Chem. Co., Inc.; initial mass-fraction purity of not less than 0.97) was purified by double sublimation at T = 310 K and p = 0.4 kPa immediately prior to measurements avoiding any contact of the substance with the air and kept over ascarite.
The mass-fraction purity of 1-aminoadamantane, determined by g.l.c. (solution in hexane, stationary phase RTX-1, column length = 30 m, carrier-gas nitrogen, flame-ionisation detector) was 0.9989.
Adiabatic calorimetry
Heat capacities at
Thermodynamic properties of 1-aminoadamantane in the condensed state
Experimental values of the molar heat capacity (Cs,m) of 1-aminoadamantane in the temperature range of (5 to 370) K are presented in table S1 and figure 2.
The extrapolation of the heat capacity of crystal crIII down to T = 0 K was carried out by the Debye function with three degrees of freedom: Cp,m = 3R · D(〈ΘD〉/T). The average Debye characteristic temperature for the studied compound, 〈ΘD〉 = (80.32 ± 0.09) K, was determined from the experimental heat capacities within (5.4 to 6.9) K, i.e. till the
Thermodynamic properties of 1-aminoadamantane in the ideal gaseous state
A procedure for statistical thermodynamics calculations for ideal gases is presented in detail in [32]. The molar mass of 1-aminoadamantane is M = 0.151249 kg · mol−1; the symmetry of its overall rotation is Cs with symmetry number σ = 1. The geometrical and spectral characteristics of the studied compound were determined in the present work according to the methods described below.
Optimisation of the molecular geometry of 1-aminoadamantane, calculations of its fundamentals and their i.r. and Raman
Thermodynamic analysis of 1-aminoadamantane synthesis
On an industrial scale, simple amines are normally obtained from their corresponding alcohols by gas-phase amination at T = (570 to 620) K in the presence of Al2O3 as a catalyst [39]. Heavier amines are usually synthesized from corresponding halides. The latter way is more complicated to realize and requires an extra stage to obtain amine form from its salt. In this work, equilibrium constants for homogeneous amination of 1-adamantanol at various temperatures were calculated (table 12):For
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