Методом обращенной газовой хроматографии изучены термодинамические характеристики сорбционного перераспределения углеводородов (н-алканов С8 С12, терпенов С10Н16, изомеров ксилола) и спиртов (алканолов С3 С5, бутандиола-2,3, ментола) в системе газсупрамолекулярный смектико-нематический жидкий кристалл 4-(3-гидроксипропилокси)-4-формилазобензол (ГПОФАБ). Установлено, что вследствие ассоциированной структуры ГПОФАБ его сорбционная емкость по отношению к немезогенным сорбатам сильно понижена, особенно в смектической А-фазе. Большие положительные отклонения от закона Рауля в исследованных системах “немезогенГПОФАБ” найдены не только в мезофазах, но и в изотропной фазе ГПОФАБ, которая, в отличие от изотропных фаз классических (неассоциированных) ЖК, обладает высокой селективностью по отношению к пара- и мета-ксилолам.
Mesomorphic, sorption, and selective properties of a three-component sorbent based on a mixture of nematic (N) liquid crystals of 4-methoxy-4′-ethoxyazoxybenzene (MEAB) and 4,4′-diethoxyazoxybenzene (azoxyphenetol, AOP) of an eutectic composition and heptakis-(2,3,6-tri-O-benzoyl)-β-cyclodextrin (Bz-β-CD) are studied. For 30 organic compounds of different classes with linear and cyclic molecular structures, including optical isomers of limonene, pinene, camphene, and butanediol-2,3, thermodynamic functions are determined for their gas-phase sorption using a three-component MEAB-AOP-Bz-β- CD sorbent (62: 28: 10 wt %). It is found that the investigated sorbent possesses high structural selectivity (αp/m = 1.128–1.059, 100–130°C, N) and moderate enantioselectivity (1.07–1.02) within a broad temperature range (95–170°C) including both mesomorphic and isotropic phases of the sorbent. It is shown that the enantioselectivity of the sorbent is apparent under conditions of both increasing retention when a chiral Bz-β-CD additive is introduced into the MEAB–AOP system (limonenes, pinenes, camphenes) and decreasing retention (butanediols-2,3).
Thermodynamic characteristics of the sorption redistribution of hydrocarbons (C8–C12 n-alkanes, C10H16 terpenes, xylene isomers) and alcohols (C3–C5 alkanols, butanediol-2,3, menthol) in a gas-4-(3-hydroxypropyloxy)-4′-formylazobenzene (HPOFAB) supramolecular smectic-nematic liquid crystal system are studied via inverse gas chromatography. The sorption capacity of HPOFAB with respect to nonmesogene sorbates is found to be strongly diminished due to its associated structure, especially in the smectic A phase. Great positive deviations from the Raoult law in the studied nonmesogene-HPOFAB systems are observed not only in mesophases, but also in the isotropic HPOFAB phase, which has a high selectivity to para- and meta-xylenes, in contrast to the isotropic phases of classic (non-associated) liquid crystals.
The thermodynamic characteristics of sorption of n -alkanes, arenes, aldehydes, monoatomic alcohols, and optical isomers of camphene and butanediol-2,3 by a chiral smectic liquid crystal, 2-methylbutyl ester of 4-(4-decyloxybenzylideneamino)-cinnamic acid, from the gas phase were studied over the temperature range including the S* C and S* A mesophases and isotropic phase. The standard and excess thermodynamic functions of sorption were determined for 26 sorbates of the classes of substances specified. The S* C and S* A mesophases exhibited selectivity with respect to the separation of para and meta xylenes (α p/m = 1.06–1.07, 90–108°C) and pronounced enantioselectivity (α R/S = 1.05–1.09, 87–108°C). The helically twisted structure of the smectic liquid crystal was shown to play an important role in the mechanism of the chiral recognition of optical isomers of polar and low-polarity compounds under gas-liquid chromatography conditions.
The thermodynamic characteristics of sorption of n-alkanes, arenes, aldehydes, monoatomic alcohols, and isomeric forms of butanediol-2,3 by chiral nematic liquid crystals, terephthalidene- bis -2-methylbutyl para-aminobenzoate, were studied over the temperature range of the existence of the meso- and isotropic phases. The contributions of dipole—dipole and specific interactions to the enthalpy of sorption were estimated. Sorbate—liquid crystal systems were characterized by positive deviations from ideality caused by the enthalpy factor. The mesophase of the liquid crystal studied was found to possess selectivity with respect to the optical isomers of butanediol-2,3 (α R/S = 1.03 over the temperature range 140–150°C). It was shown that diol–liquid crystal molecular H-complexes formed played an important role in the mechanism of chiral recognition of butanediol-2,3 optical isomers under gas-liquid chromatography conditions.
The effect of cholesteryc ether of p-pentyloxybenzoic acid mesomorphic state on its sorption properties and selectivity in relation to n-alkanes (C6–C10), benzene and its derivatives (toluene, ethylbenzene, xylenes, 1,3,5-trimethylbenzene), alcohols (C2–C6) with normal and isomeric structure, and selectivity to isomeric xylenes and alcohols separation is studied by the gas chromatography method. Due to small contribution of specific interactions in retention, division of normal and isomeric structure alcohols on columns with cholesteric ChPB as well as xylene isomers occurs on the basis of their structure.
